Declassified effects of nuclear weapons and other threats: minimizing weapons effects on civilians

Can Britain and America prevail over an alliance of Russia, China, Iran and North Korea in WWIII? American sanctions on Japan in 1940 led to Pearl Harbor on 7 December 1941, so beware of the lessons of history Mr President, and get civil defense

Wednesday, November 05, 2008

EMP effects from surface bursts, tower bursts, and free air bursts (not high altitude bursts)



Above: nuclear lightning observed in film of the 10 megatons H-bomb test, Ivy-Mike, Elugelab Island, Eniwetok Atoll, 1 November 1952 (click on photos for larger view). The nuclear lightning was visible clearly at times of 3-75 milliseconds after burst. (Images are taken from the excellent quality Atomic Energy Commission film, "Photography of Nuclear Detonations", embedded below.) The nearest lightning bolts (between the sea water around the island and the non-thunderstorm scud cloud) are both 925 metres from ground zero, and other lightning flashes at are 1,100, 1,280 and 1,380 metres from ground zero. The best estimate, by J. D. Colvin, et al., "An Empirical Study of the nuclear explosion-induced lightning seen on Ivy-Mike", Journal of Geophysical Research, v92, 1987, p5696, is that each lightning bolt carried between 150 and 250 kA. The lightning bolts curve to follow constant radii around ground zero, corresponding to equal intensities of air conductivity and EMP Compton current.






EMP ("radioflash") is also emit by conventional chemical explosives, due to the charge separation: exploding TNT ionizes some of the product molecules at a temperature of thousands of degrees C, thereby propelling some free electrons outwards faster than the heaver ions, which causes a charge separation, and thus an EMP emission, just like radio emission from electric charge moving in an antenna (in cases where there is asymmetry caused by the ground or other absorber on one side of the explosion). Chemical explosive EMP was first reported in 1954 in Nature v173, p77. The peak electric field strength falls off by the reciprocal of the cube of distance near the detonation, but only inversely with distance far away. Extensive EMP measurements were reported for TNT explosions by Dr Victor A. J. van Lint, in IEEE Transactions on Nuclear Science, volume NS-29, 1982, pp. 1844-9. He showed that chemical explosion surface burst EMP is vertically-polarized and first peaks in the negative direction (i.e. due to free electrons moving upwards, or "conventional current" moving downwards) at 8 milliseconds after detonation. The average first peak electric field strength for 46 kg of TNT ranged from -389 v/m at 35 metres distance to -5.20 v/m at 140 metres.

In chemical explosion, EMP creation is limited to the hot fireball region where air is ionized by the heat. But in a nuclear explosion, the Compton effect produces an EMP far more effectively, with gamma rays knocking electrons off air molecules in the forward direction, even well outside the hot fireball.


Above: test firing controller Dr Herbert Grier of E.G. & G at Operation PLUMBBOB in 1957 when EMP was well known (which is why - if you click on the photo for an up-close view of the Nevada nuclear test control console - you can see that it is actually very ruggedly constructed to deliberately survive EMP). During the count-down, the Nevada Test Site main power supply technicians were warned deliberately over loudspeakers just before detonation: 'Stand by to reset circuit breakers'. E.G. & G. were responsible for all American electronics at atmospheric tests in both the Pacific and Nevada. They set up the firing circuits for the bombs, laid the cables to the bomb, set up circuits linked to the firing circuit so that high-speed cameras would be turned on at the right time to film the fireball, did the count-down and 'pressed the button' (or rather, didn't press the stop button on the automatic sequence timer). For tower shots and surface bursts, EMP surges induced near the detonation of thousands of amperes were conducted in the cables back to the control point, ruining equipment and escaping by cable cross-talk (mutual inductance due to magnetic fields in the insulator between parallel unconnected cables!) into other circuits, such as the telephone system, which had to be switched over to diesel generator power at shot time to isolate it from damage. EMP fused cable conductors together, arched over porcelain insulators and lightning surger protectors, welded the contacts on relays together, permanently pegged meter dials over to full scale, and burned out other electronic components. E.G. & G. kept the EMP data secret and did not even tell the U.S. Department of Defense, which was merely measuring long-distance radiated EMP for weapons diagnostic purposes and for detecting foreign atmospheric nuclear tests. This is why close-in (source region) EMP cable pick-up and coupling damage was ignored until 30 April 1961, when B. J. Stralser of E.G. & G. wrote a Secret - Restricted Data report on all the EMP damage from the 50s tests, Electromagnetic effects from nuclear tests, which we will discuss in detail together with a Russian and British EMP effects reports from 1959, and French EMP effects reports from their first and fourth nuclear tests in the Sahara desert.

‘The objective of Mike Shot was to test, by actual detonation, the theory of design for a thermonuclear reaction on a large scale, the results of which test could be used to design, test, and produce stockpile thermonuclear weapons... Quantitative measurements of the gross explosion-induced electromagnetic signal were made possible by first displaying portions of that signal on the faces of cathode-ray tubes. The results of these efforts were excellent... On Mike Shot the early electromagnetic signal was displayed in sufficient detail to allow a rough measurement of the time delay between primary and secondary fission reactions.’

Stanley W. Burriss, Operation Ivy, Report of Commander, Task Group 132.1, Los Alamos Scientific Laboratory, weapon test report WT-608, 1953, Secret – Restricted Data, pp. 7-13.



Above: the dramatic visible EMP-related lightning bolts induced by the 10.4 Mt Ivy-Mike detonation around the fireball, Eniwetok Atoll, 1 November 1952. The nuclear lightning flashes at about 1.4 km from ground zero, around the Mike fireball, were visible in the film from 4-75 milliseconds after burst. Castle shots in 1954 produced similar effects. (Reference: M. A. Uman, et al., 'Lightning induced by thermonuclear detonations', Journal of Geophysical Research, vol. 77, p. 1591, 1972. For more up to date theoretical interpretation see: R. L. Gardner, et al., 'A physical model of nuclear lightning', Phys. Fluids, vol. 27, issue 11, p. 2694, 1984; R. F. Fernsler, Analytical model of nuclear lightning, NRL Memorandum Report 5525, 1985; and E. R. Williams, et al., 'The role of electric space charge in nuclear lightning', J. Geophys. Res., vol. 93, 1988, pp. 1679–1688. The latest research suggests that the nuclear lightning bolts around Mike fireball carried vertical currents of 100,000-1,000,000 Amperes.) The mechanism of nuclear lightning was predicted by the physicist Enrico Fermi (who developed the original theory of beta decay, and also built the first graphite moderated nuclear reactor - water moderated nuclear reactors have of course occurred naturally long ago in uranium ore seams at Gabon in Africa) in 1945, as reported by Robert R. Wilson in his ‘Summary of Nuclear Physics Measurements’ (in K.T. Bainbridge, editor, Trinity, Los Alamos report LA-1012, 1946 (declassified and released as LA-6300-H, p. 53, in 1976):

‘... the gamma rays from the reaction will ionise the air... Fermi has calculated that the ensuing removal of the natural electrical potential gradient in the atmosphere will be equivalent to a large bolt of lightning striking that vicinity ... All signal lines were completely shielded, in many cases doubly shielded. In spite of this many records were lost because of spurious pickup at the time of the explosion that paralysed the recording equipment.’

The earth has a natural vertical potential (electric field) between ground and ionosphere; the ionization of the air by bomb radiation suddenly makes the air conductive, shorting out the natural electric field and thereby inducing lightning discharges to flow vertically through the relatively conductive air.

* Link to PDF download of DNA-EM-1 “Capabilities of Nuclear Weapons” Chapter 7 “Electromagnetic Pulse (EMP) Phenomena” (40 page, 1.3 MB)

‘The generation of EMP from a nuclear detonation was predicted even before the initial tests, but the extent and potentially serious degree of EMP effects were not realised for many years. Attention slowly began to focus on EMP as a probable cause of malfunctions of electronic equipment during the early 1950s. Induced currents and voltages caused unexpected equipment failures during nuclear tests, and subsequent analysis disclosed the role of EMP in such failures.’ - Philip J. Dolan, Capabilities of Nuclear Weapons, DNA-EM-1, p. 7-1, 1978 (change 1).


Above: close-in EMP data for 100 kt and 1 Mt surface bursts on soils of various electrical conductivities. The plots shows the relationship between EMP fields (as well as air conductivity) and the peak blast wave overpressure at the corresponding distance.

Philip J. Dolan's Capabilities of Nuclear Weapons DNA-EM-1 has been discussed in previous posts on this blog, e.g. here (history of the publication) and here.

Chapter 7: Electromagnetic Pulse Phenomena (PDF download), 40 pages

This vital chapter has some graphs deleted for high altitude bursts which are now available from another document but it includes a vital set of surface burst EMP data in figures 7-25 to 7-35, showing the peak air conductivity, magnetic and radial as well as transverse electric field strengths as a function of peak overpressure for 100 kt and 1 Mt, as well as the waveforms for four locations and the frequency spectra derived from the waveforms using Fourier analysis. The graph showing the radial Compton current in a surface burst has been deleted from the chapter, but it can be seen from another report openly available on surface burst EMP physics: see Fig 3-2 on page 34 of the report by Conrad L. Longmire and James L. Gilbert, Theory of EMP Coupling in the Source Region, Defense Nuclear Agency, report DNA 5687F, DTIC document reference ADA108751. Also Fig 3-3 on page 37 gives air conductivity, although this data is only partially deleted from DNA-EM-1 Chapter 7, since although one graph of air conductivity versus time at 500 m distance is deleted, another set of curves giving air conductivity versus time for four separate distances corresponding to various peak air blast overpressures which include 500 m for the highest intensity, are available.

It should be emphasised that this data on the close-in or 'source region' EMP in surface bursts is vital for civil defence because the EMP damage in such bursts doesn't occur due to radiated EMP but instead occurs due to the coupling of the strong short-range EMP fields into metallic conductors like electric cables, pipes, railroad tracks, etc., near ground zero which then carry an electric current surge outward at the velocity of light for the insulator. The EMP damage in a surface burst occurs because of the many thousands of amperes of EMP electric current induced in such conductors which is carried out by such conductors to great distances from the burst point with little attenuation, getting distributed throughout the electric power grid out to tens or hundreds of miles away, where it causes damage to unprotected electrical and electronic equipment. The radiated EMP signal from a surface burst is usually too weak to cause much permanent damage to equipment (apart from the case of very tall vertical antenna such as radio transmitter masts). Instead, the serious threat is the electric current pulse induced in cables by the close-in radial electric field of a surface burst, which is piped out of the source region by long cables stemming from the source region (which carry the EMP away at light speed long before they are damaged by the slower moving ground shock, blast wave and cratering action). This is the cause of the long-distance devastating problem of EMP in power networks and communication line far away from a surface burst.

This has been well demonstrated at nuclear tests where the bomb was detonated by cable control, with the cables carrying back EMP as an electric power surge to the control point and damaging the control panel and its power network equipment. This effect was first publically documented by Bernard O'Keefe of EG & G - Edgerton, Germeshausen and Grier - in his 1983 book 'Nuclear Hostages' for the three 1948 Sandstone tests which were cable controlled at Eniwetok. Free air bursts like Crossroads-Able and many early tests at the Nevada in 1951 did not cause this effect because the bombs did not have any cables nearby to pipe out an electric signal. The Crossroads-Baker underwater test was set off by radio signal to the ship above the bomb (which was soon blasted to pieces by the shock wave anyway), preventing any direct cable connection between the control ship and the bomb itself, so no EMP damage problems were there reported.

In the British underwater Hurricane test of 1952, there were EMP damage problems because of the use of cables and radio signals from the ship carrying the bomb to recording stations. British nuclear test scientist N. F. Moody set up an experiment involving electric cables running from the Hurricane nuclear bomb ship (HMS Plym) at Monte Bello, Australia, designed to carry gamma radiation dose rate data for Hurricane to a magnetic tape recorder at a safe distance from the blast effect, to measure the bomb’s nuclear reaction acceleration rate on a nanosecond time scale. But immense EMP energy carried by those cables burned out the instruments, leading to extensive British research into EMP. By 1957, at the British nuclear tests Operation Antler in Australia, the gamma ray spectrometer (to determine the spectrum of the initial gamma radiation flash) was specially protected against EMP interference by using an electric power supply sealed in a steel locker, with all the electric cables running through sealed metal pipes to the instrument.

‘It was necessary to place most of the [1945 Trinity nuclear test measurement] equipment in a position where it had to withstand the heat and shock wave from the bomb, or alternatively to send its data to a distant recording station before it was destroyed. We can understand the difficulty of transmitting signals during the explosion when we consider that the gamma rays from the reaction will ionise the air... Fermi has calculated that the ensuing removal of the natural electrical potential gradient in the atmosphere will be equivalent to a large bolt of lightning striking that vicinity [this is precisely what was actually photographed around the fireball of the Mike 10.4 Mt thermonuclear test in 1952, see top of this blog post for the photograph and literature references for nuclear lightning] ... All signal lines were completely shielded, in many cases doubly shielded. In spite of this many records were lost because of spurious pickup at the time of the explosion that paralysed the recording equipment.’

Robert R. Wilson, ‘Summary of Nuclear Physics Measurements’, in K.T. Bainbridge, editor, Trinity, Los Alamos report LA-1012, 1946 (it was only declassified and released as LA-6300-H, p. 53, in the year 1976).

‘[At the Sandstone-X Ray 37 kt nuclear test on April 15, 1948, from a 200 ft tower on Enjebi Island at Eniwetok Atoll] we had to watch the control panel [in the control room 30 km away] ... lights flashed crazily on and off and meters bent their needles against their stop posts from the force of the electromagnetic pulse travelling down the submerged cables with the speed of light... one of our engineers, halfway around the world in Boston... was able to detect [the radiated EMP or radio-flash] with a makeshift antenna and an oscilloscope, the world’s first remote detection measurement.’

Bernard J. O’Keefe (President of Edgerton, Germeshausen and Grier, Inc.), Nuclear Hostages, Houghton Mifflin, Boston, 1983.

On 30 April 1961, B.J. Stralser’s report Electromagnetic effects from nuclear tests, Edgerton, Germeshausen and Grier, Inc. (classified Secret – Restricted Data) was the first official American secret report produced summarising the physical damage due to EMP on the power distribution system, telephone system, and testing control equipment at the Nevada test site, due to small surface and near surface (tower) bursts:

1. The radial electric field of the EMP induced electric currents of thousands of amps in bomb electrical cables at 800 m from ground zero, breaking down cable insulation, fusing multicore conductors together, and actually melting the protective lead sheathing surrounding “hardened” cables.

2. EMP opened the circuit breakers at the Nevada test site’s power supply, 50 km from ground zero. Order to technicians at the main power supply, before tests: “Stand by to reset circuit breakers.”

3. Instrument stations have to use power from internal batteries or nearby diesel generators, to avoid EMP pick-up and distribution to equipment with long power cables.

4. In the test control room: fuses were blown, meters overloaded with bent needles, a carbon block lightning protector was permanently shorted to ground, with current arcing over porcelain cut-outs.

5. EMP currents fused the contacts and melted off the pins on electromagnetic relays.

6. The Nevada test site telephone system had to be switched to diesel generator power during tests.

7. Radar oscilloscopes showed the induced transient EMP effect as a “ball of yarn” and “bloom”.

After the EMP damage effects to electronic piezo electric blast gauge chart recorders at the first ever nuclear test Trinity on 16 July 1945, and the EMP damage to the control console dials at Sandstone tests in 1948, the next serious EMP problems apparently occurred with the 1.2 kt Jangle-Sugar test of 1951, which was the first ever cable-controlled test in the Nevada Test Site (after a series of free air burst bombs dropped from aircraft, the detonation of which were controlled by timer/radar sensors instead of by wired cable control).

The bomb control cables from the Sugar test explosion were apparently fused together by over 1000 Amperes at 0.5 mile distance, and the electric EMP power surge in the cable caused a lot of damage at the control point 30 miles away, arching over porcelain cutouts, fusing the contacts of relays together, driving meters off-scale, and apparently escaping by cable cros-talk into other circuits including into the power grid and tripping distant circuit breakers in Las Vegas some 90 miles from the burst. As a result, all further cable-controlled tests at Nevada had to take the precautions of switching off mains power at the Nevada control point at shot time and running the telephone system and other equipment off diesel generators to prevent the EMP power surge escaping into cables to the national power grid.

Technicians were also warned over the loudspeaker during the countdown to 'Standby to reset circuit breakers' after the EMP at shot time. Nevada EMP facts are documented in a 'Secret-Restricted Data' report dated 30 April 1961 by B. J. Stralser of E. G. and G. (Edgerton, Germeshausen and Grier) - which was responsible for doing the countdowns and firing systems at American nuclear tests - called 'Electromagnetic Effects from Nuclear Tests'. E.G.G. were famous for high-speed photography and its associated electronic timing circuits, and it was in this connection that the company was recruited by the Manhattan Project to develop high-speed filming techniques for nuclear tests, which of course had to be set off by an electric signal from the bomb activation mechanism, and this is the reason why they ended up in charge of the timing and firing side of the bomb.

In his book Nuclear Hostages, O'Keefe (head of E.G.G. in 1983) explains how he wired up the Nagasaki bomb's implosion system on Tinian Island, changing an incorrect cable connector with a soldering iron on the assembled bomb so it could be dropped on schedule. At the Nevada test site, the control signal to the bomb in cables was also used to set off high speed cameras and other instrumentation electronics, so E.G. & G. ended up expert in the experimental study of EMP damage by cross-talk between parallel cables and different adjacent circuits. It is clear that there was during the 1950s a problem in getting this secret EMP damage data away from E.G. & G. - who viewed it as a technical nuisance - to the people interested in the damaging effects of nuclear explosions.

Most of the interest in EMP in 1951 by the military was in the use of the radiated radioflash EMP - the well known click on radio receivers when a nuclear bomb flash goes off - as a convenient electronic means to remotely detect and identify a nuclear explosion, which has nothing to do with the damaging effects of EMP piped out of the source region by conductors like cables.

Even as late as 1957, only a very brief single-paragraph discussion of EMP pick-up effects from low altitude and surface bursts occurs in the November 1957 edition of the Confidential (classified) U.S. Department of Defense, Armed Forces Special Weapons Project manual TM 23-200, Capabilities of Atomic Weapons, section 12, “Miscellaneous Radiation Damage Criteria”, page 12-2, paragraph 12.2c:

Electromagnetic Radiation. A large electrical signal is produced by a nuclear weapon detonation. The signal consists of a rather sharp transient signal with a strong frequency component in the neighborhood of 15 kilocycles. Field strengths greater than 1 volt per metre have been detected from megaton yield weapons at a distance of about 2,000 miles. Electronic equipment which responds to rapid, short duration transients can be expected to be actuated by pickup of this electrical noise.”

Notice that they are completely ignoring the source region cable EMP pick-up problem that E. G. and G. had identified with nuclear tests since 1948 in the Pacific (Operation Sandstone cable-controlled tower bursts) and 1951 (Nevada cable-controlled Sugar shot, etc.), and just commenting on the long-distance radiated EMP as an 'electrical noise' problem! The source-region radial EMP in a surface burst or near surface burst is on the order of 100,000 v/m, and it is the pick-up of this EMP which induces massive currents in cables that then disperse it outside the source region. The radiated EMP outside the source region is weak so it has nothing to do with the damage problem in low altitude bursts! So EMP information was stuck with the people dealing with EMP damage in cables, and it wasn't even getting into the classified manual!

The major reference on the physics of cable pick-up from the source-region which is cited by Dolan's DNA-EM-1 secret manual is Dr Conrad L. Longmire's report Ground Fields and Cable Currents Produced by Electromagnetic Pulse from a Surface Nuclear Burst, DASA 1913, DASIAC SR-54, Defense Atomic Support Agency, March 1968. It is clear that the partitioning of secret departments in the 1950s was responsible for nuclear test data on EMP damage not being widely recognised as a civil defence and also a military problem until the 1960s when substantial funds were allocated to do serious research into EMP mechanisms for damaging effects.

One of the major problems in generalizing EMP pickup into conductors from the source region is that the EMP coupling into cables depends on the ground permittivity or dielectric constant and the conductivity of the ground, which are both dependent upon the EMP wave frequency, depending very strongly on the moisture and salt content of the soil, a problem first analysed fully by Smith and Longmire in the October 1975 report A Universal Impedance for Soils, DNA 3788T. Longmire has also written a brief and simple account of another EMP problem, the System Generated EMP, SGEMP or 'Direct Interaction' EMP, caused by nuclear radiation striking electrical and electronic systems and inducing EMP pulses directly without the mediation of EMP fields: Direct Interaction Effects in EMP, DNA 3249T, 1974.

THE RADIATED EMP AT GREAT DISTANCES FROM AN AIR BURST AND FROM A SURFACE BURST

FIRST OPEN RUSSIAN PUBLICATION ABOUT NUCLEAR BOMB EMP IN 1958

The declassification of the existence of radiated EMP/radioflash for the 1962 edition of The Effects of Nuclear Weapons (the first edition to mention it) was finally triggered by Russia! It was the fact that Russia was concerned with EMP damage that forced America to start taking the threat seriously and to do detailed investigations, getting E.G. & G. to write the report on EMP damage in nuclear tests.

In December 1958, Russian scientist A.S. Kompaneets published openly a theory of “Radio Emission from a Nuclear Explosion” (Zh. Eksperim. I Teor. Fiz., Vol. 35, pp. 1538-42), which was later discredited by Dr Victor Gilinsky of the RAND Corporation in California, because Kompaneets actually ignored the Compton current (which is the essential mechanism!) and only calculated the effect of the late ionic current in air (which is insignificant and of positive polarity), so that Kompaneets’ predicted EMP waveform misses out the massive fast-rising negative electric field due to the Compton current, and only features the small, delayed, positive electric field due to the ionic current!

Russian data on EMP had come not from measuring the EMP by photographing the pulse on oscilloscope screens like American and British work, but by measuring the distance sparks would jump over spark gaps, and by assessing the burn out of electronic equipment. So Russian work was concerned with directly measuring end effect of induced current EMP pulses, not the sophisticated measurements of the free field EMP waveforms radiated in the air by the explosions. The stimulus of the Russian article in December 1958 coincided with the first secret British-American exchange of EMP data that same month (although the English translation of Kompaneets paper was not published until June 1959 in J. Exptl. Theoret. Phys. (Soviet Physics JETP), volume 35, No. 6, June 1959, page 1076), which paved the way for the Minuteman missile system to be protected against EMP in 1960, the very first American military system to be designed to withstand EMP!

Although close in EMP damage and distant ‘radio-flash’ (clicks on radio sets) were experienced at the Trinity nuclear test in 1945 and the Sandstone tests in 1948, regular measurements of the EMP waveforms from nuclear tests only began in 1951 at Operation Buster-Jangle in the Nevada desert. M.H. Oleson was in charge of Project 7.1, ‘Electromagnetic Effects from Atomic Explosions’ which was maintained throughout Operations Tumble-Snapper (report WT-537, 1953), Upshot-Knothole (report WT-762, 1955), Ivy (report WT-644, 1958), and Castle (report WT-930, 1958).

Oleson's measurements at 20 km from ground zero in surface and near-surface bursts of yields ranging from 1-20 kt gave vertically polarised electric fields peaking within 1 microsecond at 100-300 v/m in the negative direction. He found that at large distances of 1500 km the direct pulse was distorted and extended by a factor of 10, due to multiple ‘sky wave’ reflections back from the Earth’s conductive ionosphere (80 km altitude). During Operation Castle in 1954, for example, 17 oscilloscope stations measured 74 sets of EMP data, at distances ranging from 23 km to 12,000 km. Vertical aerials 2 metres high for close-in stations and 10 metres high for distant stations were used, with cameras fixed to photograph the screens of oscilloscopes (an ingenious electronic circuit system was used to prevent over-exposure of the film, keeping the electron beam trace off the oscilloscope screen until the last moment before the detonation!). These waveforms showed the internal dynamics of the weapons (the magnitude of the EMP showed the fission yield, while the time delay in the EMP rise steps showed the delay between the fission ‘primary’ and the fusion ‘secondary’ ignitions occurring inside the weapon).



Above: air burst EMP due to vertical asymmetry (air density falling with increasing altitude) where the upward Compton current is stronger than the downward Compton current, because the gamma rays causing it penetrate further in the low density air. This illustration for radiated EMP within 100 km of air bursts (before distortion and increased duration occurs at great distances) is from Dolan's DNA-EM-1, Capabilities of Nuclear Weapons, 1978 update, chapter 7. The approximate numbers stated for peak fields are for typical bomb yields ranging from 1 kt to 10 Mt and burst heights from sea level to 30 km altitude. The smaller sizes and fields correspond to lower yields and burst altitudes and the the bigger sizes correspond to the greater yield and burst altitude. E.g., ~30 v/m is for ~3 km horizontally from a 1 kt sea level air burst, and ~300 v/m is for ~14 km horizontally from a 10 Mt air burst at 30 km altitude. (See Glasstone and Dolan, pages 517-8 and 534-5.)



Above: vertically polarized EMP waveform due to vertical air density gradient induced Compton current asymmetry from an unspecified approximately 1 kt so-called 'air burst' test at about 900 m altitude, at seven different distances (44.6 km to 4,828 km) from ground zero. Actually, the downward prompt gamma radiation shell moving at light velocity, 300 million metres per second or 300 metres per microsecond, hit the ground 900 metres below the bomb after just 3 microseconds; so from 3 microseconds onwards, the radiated EMP phenomena approximated that from a ground surface burst, which is much stronger than EMP radiated due to air density asymmetry in a true air burst which doesn't interact with the earth's surface. As the distance from ground zero increases, ionospheric reflection phenomena always greatly lengthens (stretches out) the EMP waveform, increasing the effective rise time to maximum field strength, and therefore reducing the maximum frequency of the EMP.



Above: illustration of the EMP measured from the Chinese 200 kt shot of 8 May 1966 from an interesting Norwegian Defense EMP compendium (which also includes other measured EMP waveforms from Chinese air bursts) by Karl-Ludvig Grønhaug (who has other EMP reports linked from his page here). It shows the electric-dipole EMP waveform due to vertical asymmetry from a typical air burst after it has been distorted and greatly extended in rise time and duration by ducting between ionosphere and ground over a distance of 4,700 km. The peak EMP measured at 4,700 km from four Chinese detonations are:

8 May 1966: 200 kt air drop bomb gave E = 40 millivolts/metre at 4,700 km
27 October 1966: 20 kt missile test gave E = 40 millivolts/metre at 4,700 km
27 December 1966: 300 kt tower shot gave E = 140 millivolts/metre at 4,700 km
27 December 1968: 3 Mt air drop bomb gave E = 22 millivolts/metre at 4,700 km


To calculate the electric-dipole radiated EMP theoretically, you need to work out the net vertical electric current variation as a function of time (allowing for the increase in air conductivity due to secondary electrons knocked off atoms by the primary Compton electrons, and the reversed conduction current opposing the Compton currents that results from the secondary electrons), and this net varying current or acceleration of charge allows you to work out the radiated EMP using Maxwell's equations.

This isn't that hard to understand what is occurring if you think intuitively about the physics involved. The major contribution to the net Compton current for the first microseconds that are most important is the prompt gamma ray shell, going outward at light velocity, 300 metres per microsecond. So we concentrate on that pulse for now and ignore later (less intense) gamma ray emission. The total radial outward Compton current is then simply the prompt gamma ray emission multiplied by (a) the proportion of Compton scatterings which result in net outward electron motion, and (b) the fraction of the prompt gamma rays which have undergone Compton scatterings up to time t.

Since the mean-free path for typical 2 MeV prompt gamma rays is 174 m in sea level air (and greater than this in less dense air, scaling as the inverse as air density), so the fraction of prompt gamma rays that have undergone Compton scattering when the radiation front (moving at velocity c = 300 metres/microsecond) is at radius R = ct metres is simply f = 1 - e-R/174 = 1 - e-ct/174 = 1 - e-300t/174 = 1 - e-1.72t for t in microseconds and for sea level air (but remember that the mean free path of 174 metres has to be altered as a function of time because as the shell goes upwards, it goes into less dense air, so the mean free path increases; in an air burst the downward shell does into denser air so the initial mean free path for that hemisphere gets smaller with time - also in an air burst 174 metres needs to be replaced with the air density at the burst altitude, unless it is a sea level air burst).

Because this upward Compton current is in the opposite direction to Franklin's definition of conventional electric current (which is the direction that positive charges move, i.e. the opposite direction to the motion of electrons), this initial net 'conventional' electric current in a surface burst is negative (the opposite direction by definition to net the flow of Compton electrons). We can easily adapt this equation to include air density variation in the vertical direction, and then for an air burst we need to write two versions of this equation: one for the hemisphere above the bomb and another for the hemisphere below it. By subtracting the latter from the former, we get the net vertical Compton current variation as a function of time in an air burst. Dividing that into the net vertical current in a surface burst, gives us the ratio of net vertical Compton currents for air and surface bursts as a function of time after burst.

There is later a positive pulse of conduction electrons because the 2 MeV prompt gamma rays produce 1 MeV Compton electrons, which soon get slowed down by colliding with air molecules and knocking off 'secondary electrons' from those air molecules. Since it takes 34 eV to knock an electron off an atom, each 1 MeV Compton electron produces 29,000 secondary electrons, which increase the air's conductivity and cause a 'return current' that opposes (and eventually shorts out) the Compton current, predominating after a few microseconds. Ion-electron plasma oscillations, and contributions of radiation from neutron scatter gamma rays, decaying fission products, and neutron capture gamma rays then produce the long 'tail end' to the EMP.

The integrated net upward vector current going in the upper hemisphere of air is equal to exactly 1/3rd of the total radial Compton current in that hemisphere. However, although this looks like a similar situation to a simple vertical dipole antenna in radio transmission theory, in fact it's a lot more difficult than a simple radio transmitter calculation, because much of the net radial currents in surface and air bursts exist within a region of ionized conductive air, which attenuates the radiated EMP to some extent before it can escape from the gamma ray deposition region to large distances. This is why detailed computer calculations are needed to accurately predict EMP field strengths radiated from air and surface bursts: early theoretical efforts in the 1950s and 1960s usually over-estimated the radiated EMP from such bursts by ignoring the attenuation.

An interesting empirical finding reported in the 1950s Nevada and Pacific investigations on the EMP radiated from surface bursts is that the median frequency of the EMP gets smaller for higher yields: the median frequency measured 20 km away is 41,000/H Hertz (Hz), where H is the effective height of the source region which is behaving as a vertical antenna in a surface burst. For yields of 1 kt to 1 Mt, H increases from about 1.5 to 4 km, so that the median EMP frequency in a surface burst actually falls with increasing yield, from about 30 kHz for 1 kt to about 10 kHz for a 1 Mt detonation.

In a surface burst, the EMP waveform is similar but the first half cycle is the most intense: basially the air burst EMP waveform is the surface burst EMP waveform multiplied by a correction factor which increases from 0 to 1 as time progresses. Initially, the air burst radiated EMP is weaker than that for a surface burst because the vertical asymmetry takes time to gradually increase as the radiation region extends outwards in all directions at 300 metres per microsecond. But at very late times, the EMP waveform for an air burst and a surface burst are identical. So the main difference is that the first half-cycle (the negative initial pulse) of the EMP is strongest in a surface burst, while in an air burst the second (positive) half cycle is strongest:


Above: surface burst EMP measured at a distance of 320 km from a high-yield Pacific nuclear test. It peaks after 4 microseconds at about -26 v/m in the first (negative) half-cycle. The rise time and duration is much greater in this example than surface burst EMP measured at 20 km distance. The greater the distance from the surface burst, the longer the peak intensity rise time, because the EMP wave form gradually loses higher frequencies as it propagates.

Above: Norwegian computer calculations that attempt to give an idea of the transverse (radiated) EMP waveforms from a 1 kt surface burst at distances of 1 km and 10 km, but they exaggerate the predicted intensities probably because they do not properly include the attenuation of the pulse from the net vertical currents by the ionized air through which they must travel before escaping from the conductive air of the deposition region: but at least they do indicate a much briefer rise time of the radiated EMP at distances near the detonation. There are far more comprehensive computer calculations of the surface burst close-in EMP in Chapter 7 of Dolan's DNA-EM-1, Capabilities of Nuclear Weapons.

Above: surface burst radiated EMP description from Chapter 7 of Dolan's DNA-EM-1, Capabilities of Nuclear Weapons.

Above: EMP from the 5.9 kt Hardtack-Holly surface burst (4 metres burst altitude on a barge) at Eniwetok Atoll on 20 May 1958, as recorded 8,000 km away in Los Angeles. Notice that it is completely distorted and grossly extended in duration with the initial half-cycle now positive instead of negative; this is purely a distance-related distortion effect (the loss of the higher frequencies occurring while pulse propagated between ionosphere and ocean around the Earth) and doesn't indicate the shape of the EMP waveform nearer the detonation which peaked in the negative direction at a much earlier time.

FIRST AMERICAN OPEN PUBLICATION ABOUT EMP IN 1959

The first American unclassified (open) article about EMP was published in Nucleonics volume 17, August 1959, page 64-73. This was an article by Dr J. Carson Mark of Los Alamos (Director of the Theoretical Division there from 1947-72), entitled 'The Detection of Nuclear Explosions'. Dr Mark points out that radiated EMP or radioflash can be used to detect nuclear explosions thousands of kilometres away, but he does not mention the damaging effects of EMP.

SECOND RUSSIAN PAPER ON EMP PUBLISHED OPENLY IN 1960

Then in 1960, a second important Russian paper appeared on EMP, by O. I. Liepunskii, 'Possible Magnetic Effects from High-Altitude Explosions of Atomic Bombs', J. Exptl. Theoret. Phys. (Soviet Physics JETP), volume 38, pp. 302-4, January 1960. Liepunskii there pointed out that the hot ionized fireball of a nuclear explosion is electrically conductive and will push out the Earth's magnetic field lines as it expands, producing a weak slow MHD-EMP. However, as with Kompaneets, Liepunskii misses the mechanism for the intense and rapid first pulse of the space burst EMP! Further confusion was added when in 1960 the Physical Review published a paper by physicists at the Aeronutronic Division, Ford Motor Company, and Lawrence Radiation Laboratory on a thermal X-ray mechanism for EMP generation by high altitude bursts:

'The thermal x-rays produced by a nuclear burst in outer space cause polarization currents in the medium which, if distributed anisotropically, will emit electromagnetic radiation. Roughly, a burst of thermal x rays, equivalent in energy to 1 ton of high explosive, produces a detectable 10-Mc/sec signal at a range of 1 km. Since only the ratio of x-ray energy to range enters into the strength of the radiated signal, other ranges follow by adjusting the x-ray energy proportionately. This works up to ~3×103 km; beyond this range, dispersive effects begin to reduce the signal received. The power in the electromagnetic signal varies as the square of the electron density, so this effect may provide a sensitive measure of the density of electrons in outer space.' - Montgomery H. Johnson and Bernard A. Lippmann, 'Electromagnetic Signals from Nuclear Explosions in Outer Space', Physical Review, vol. 119, Issue 3, pp. 827-828 (1960).

FIRST OPEN FRENCH PAPERS ON BOTH RADIATED AND RADIAL (IMMENSE EMP CURRENTS INDUCED BY CLOSE-IN CABLES) FROM ITS FIRST AND FOURTH NUCLEAR TESTS IN THE SAHARA, 1960 AND 1961

The peak EMP at the first French low altitude nuclear explosion in the Sahara, Africa, in 1960 (70 kt) was measured in Paris and openly published to be 0.1 v/m. See M. J. Delloue, ‘L'eclair magnetique du test nucleaire du 13 fevrier 1960 a' Reggane,’ Compt. Rend., vol. 250 (issue 11), page 2536 (1960)

A second French paper giving nuclear test EMP data was more startling for it described the successful measurement of the induced cable currents from a nuclear explosion: J. Ferrier and Y. Rocard, ‘Measure du courant electrique total fourni par une explosion nucleaire’, Compt. Rend., vol. 263, page 2931 (1961).

Ferrieu and Rocard's paper, ‘Measurement of the total electrical current furnished by a nuclear explosion’ (Compt. rend., Vol. 253, 18 December 1961) gives details of an EMP coupling experiment at the fourth French nuclear test, code named Green Gerboise (GERBOISE VERTE), a 1 kt plutonium core tower shot in the Sahara desert at Regganne, Algeria, on 25 April 1961. A network of 250 cables was laid radially, outward from around ground zero (under the tower) to several hundred metres on the poorly conducting desert sand, and the collected EMP current was conducted using a thick brass cable out to a measuring station located at 3 km ground range, where the EMP induced in the cables near the explosion (by the radial electric field) was measured to peak some 20 microseconds after detonation at 150,000 Amperes, falling to zero at 150 microseconds after detonation, and then producing a second peak of 56,000 Amperes, with opposite polarity to the first peak. This immense EMP current shows clearly the magnitude of the threat when a network of cables around the explosion can capture a massive amount of current from the radial electric field (due to radial charge separation) within 3 km of a surface burst, and carries the current out to damage equipment far from the source of the current.

HIGH ALTITUDE EMP TEST EFFECTS FROM RUSSIAN AND AMERICAN TESTS IN 1962

Finally in 1962, when America finally realized just how widespread and potentially devastating the EMP was after Starfish, and when it could detect high altitude Russian explosions investigating the same effects (three tests of 300 kt each at 59-290 km altitudes), President John F. Kennedy announced publically that America was investing in military electronic systems which cannot be “blacked out, paralysed, or destroyed by the complex effects of a nuclear explosion.” As a result of this heightened interest in EMP damage prevention, a discussion of EMP mechanisms was included in the April 1962 edition of The Effects of Nuclear Weapons, pages 502-506 of Chapter X, Radio and Radar Effects (the 1962 section on EMP is quoted in full on the previous blog post here, with criticisms),



AMERICA FINALLY CONDUCTS NEVADA NUCLEAR SURFACE BURSTS IN 1962 FOR THE PRIMARY PURPOSE OF MEASURING THE EMP PICK UP BY CABLES WITHIN THE SOURCE REGION

Following on from the reported EMP pick up at the fourth French test in the Sahara, three Nevada surface bursts in 1962 attempted to document EMP ground fields and cable currents, to varying degrees of success (there were many instrument problems).

On 7 July 1962 the 0.022 kt plutonium bomb test 3 feet above the ground in Nevada, Little Feller II, was documented for determining EMP induced damage effects (rather than merely the waveform for weapons diagnostics or the detection/location of nuclear tests or bomb attacks) for the first time in American testing history (although in 1957 Harry Diamond had measured the magnetic field component of EMP from Operation Plumbbob in Nevada for the purpose of assessing whether EMP would set off magnetic mines, they were not concerned with EMP damage to electronics). It was a standard U.S. Army tactical 'Davy Crockett' miniature nuclear bomb. An electric cable buried at a depth of 30 cm was located from 15 metres of ground zero radially outwards, and the induced EMP current pulse in the cable was measured at various distances by digital meters which saved their data on protected magnetic tape recorders. This experiment was repeated at the 0.5 kt Johnie Boy U-235 bomb test on 11 July 1962, which was detonated 58 cm underground. On 14 July 1962, the 1.65 kt plutonium bomb test Small Boy detonated 10 feet above ground was instrumented to document a complete set of EMP waveforms for radial and transverse electric field, azimuth magnetic field, and the air conductivity variation with time at distances of 190 to 3000 metres from ground zero.

(References: V.E. Bryson, et al., "Weapons Effects Testing, EM Pulse, Project 6.1", Boeing Company, Operation Dominic II, weapon test report WT-2226, June 1963, Secret - Restricted Data. Paul A. Caldwell, et al., "Magnetic Loop Measurements, Project 6.2", Harry Diamond Laboratories, Operation Dominic II, weapon test report WT-2227, February 1965, Secret - Restricted Data. R.W. Frame, "Electromagnetic Pulse Current Transients, Project 6.5", Sandia Corporation, Operation Dominic II, weapon test report WT-2230, October 1963. D.B. Dinger, "Response of Electrical Power Systems to Electromagnetic Effects of Nuclear Detonations, Project 7.5", U.S. Army Engineer Research and Development Laboratories, Operation Dominic II, weapon test report WT-2241, June 1963.)

According to the 'DTRA Factsheet on Operation Dominic II':

'Operation DOMINIC II was an atmospheric nuclear test series conducted by the Atomic Energy Commission (AEC) at the Nevada Test Site (NTS) from July 7-17, 1962. The operation consisted of four low-yield shots, three of which were near-surface detonations and one a tower shot. One of the near-surface shots was fired from a DAVY CROCKETT rocket launcher as part of Exercise IVY FLATS, the only military training exercise conducted at DOMINIC II. An estimated 3,900 Department of Defense (DoD) personnel participated in Exercise IVY FLATS, scientific and diagnostic tests, and support activities. The series was intended to provide information on weapons effects and to test the effectiveness of the DAVY CROCKETT weapon system under simulated tactical conditions. Also known by the DoD code name of Operation SUNBEAM, DOMINIC II was the continental phase of DOMINIC I, the atmospheric nuclear test series conducted at the Pacific Proving Ground from April to November 1962. ...

'The scientific tests at DOMINIC II were supervised by the Defense Atomic Support Agency (DASA) Weapons Effects Test Group. These tests were designed to collect information on weapons effects, such as the electromagnetic pulse, prompt and residual radiation, and thermal radiation. The experiments also tested the effects of low-yield detonations on structures and on aircraft in flight. ...

'The event involving the largest number of DoD participants was Shot LITTLE FELLER I, the fourth DOMINIC II test. LITTLE FELLER I was a stockpile DAVY CROCKETT tactical weapon, fired as part of Exercise IVY FLATS. This training exercise consisted of an observer program and a troop maneuver. Observers in bleachers about 3.5 kilometers southwest of ground zero wore protective goggles while they watched the detonation. Maneuver troops forward of the observation site were in trenches during the detonation. Five personnel from the IVY FLATS maneuver task force launched the weapon from a rocket launcher mounted on an armored personnel carrier. LITTLE FELLER I detonated on target, 2,853 meters from the firing position. ...

'The DOMINIC II event involving the largest number of DoD projects was Shot SMALL BOY. Originally scheduled for 31 DoD projects, the shot ultimately included 63 DoD projects, as well as four Civil Effects and 31 AEC projects. Shot SMALL BOY had initially been planned as the one detonation of Operation DOMINIC II. The primary purpose of the detonation was to provide information on electromagnetic pulse effects. Headquarters, DASA, consequently assigned Harry Diamond Laboratories, which had collected electromagnetic pulse data at Operation PLUMBBOB (1957), to provide overall technical direction for DoD programs. Program 6, Electromagnetic Effects, was given priority over the other programs, which were conducted according to strict guidelines designed to assure noninterference with Program 6 objectives. [Emphasis added: note that SMALL BOY was primarily an EMP effects test, which indicates the priority being given to EMP in 1962!]'

OLDER MATERIAL (NEEDS EDITING):

One of the immediately perplexing things about the radiated EMP or radioflash signal from a nuclear explosion in the American treatment e.g. DNA-EM-1 chapter 7 is the talk of a 'source region' or 'deposition region' boundary, symbolized by R0, which doesn't actually exist in the physical world! The radiation fields drop off gradually so there is no natural limiting distance! This problem is resolved clearly by an arbitrary definition of the radius, as explained by Glasstone and Dolan, The Effects of Nuclear Weapons, 3rd ed., 1977, page 535: 'the deposition region does not have a precise boundary, but R0 is taken as the distance that encloses a volume in which the [peak air] conductivity is 10-7 mho [1 mho = 1 S in SI units] per metre or greater.'

The Capabilities of Nuclear Weapons Chapter 7, 1978 Change 1 page 7-7 et seq says that the radiated EMP electric field strength at this radius varies from 1,300 v/m for 1 kt surface burst to 1,670 v/m for 10 Mt surface burst, but "For most cases, a value of 1,650 volts per metre may be assumed. At ranges along the surface beyond R0, the peak radiated electric field varies inversely with the distance from the burst." Dolan then gives examples of surface burst radiated EMP: for 100 kt at a ground distance equal to the deposition region radius for this yield of R0 = 5.8 km you get about 1,650 volts/metre radiated EMP, and for 1 Mt at the deposition region radius R0 = 7.2 km, you also get about 1,650 volts/metre. Scaling inversely as distance, Dolan shows that at 10 km ground range, the radiated EMP peak electric field is about 950 v/m for 100 kt surface burst and about 1,200 v/m for 1 Mt. These are small electric fields from the perspective of EMP damage concerns, although they will induce large current pulses in long conductors. One important point to notice is that the radiated EMP from a surface burst is vertically polarized (a horizontally propagating transverse wave) so it poses a threat to long vertical conductors like radio masts, not to long horizontal conductors like telephone or power cables. The source region radial electric field is horizontally polarized (radially directed, not transverse) so it causes the threat to horizontal cables and power lines, etc. In the event of a high altitude nuclear explosion, the EMP radiated downwards is polarized predominantly in the horizontal direction, so it is picked up in horizontal cables and power lines. The radiated EMP from a surface burst, apart from being relatively weak, has the wrong polarization to cause significant pick up in horizontally laid conductors, so it is not a primary damage threat.

As for the waveform of the radiated EMP from a surface burst, it's easy to get this by integrating the upward (vertical vector) component of all the Compton (electron) currents in the air above the detonation, and using this net vertical current to calculate the radiated waveform of the EMP, just as you can calculate the radiated radio waveform from a known electron current applied in a vertical antenna or aerial by a radio transmitter set. Radio waves are radiated whenever a net electric current varies with time. I.e., whenever there is a net acceleration of electric charge, as given by Larmor's simple formula for radiated power: P = q2a2/{6*Pi*Permittivity of free space*c3} watts, where q is charge and a is the acceleration of that charge. However, Larmor's formula needs relativistic corrections (see equation 8 in Mario Rabinowitz's paper) which for circular (constant pitch and radius) deflection makes their velocity vector perpendicular to their acceleration vector, giving v * a = 0, so the relativistic correction to Larmor's formula amounts to multiplying it by {gamma}4, where {gamma} = [1 - (v/c)2]-1/2, the relativistic Lorentz-FitzGerald factor:

P = q2a2[1 - (v/c)-2]2/{6*Pi*Permittivity of free space*c3} watts,

This is confirmed by Professor Bridgman's Introduction to the Physics of Nuclear Weapons Effects (1st edition, Defense Threat Reduction Agency (DTRA/DTRIAC), July 2001), equation 11-3 on page 376, where acceleration a2 in the Larmor non-relativistic equation is replaced by {gamma}2(dp/dt)2/m2, where m is the electron's rest mass, with the note that the relativistic "gamma" factor must also be included in the expression for momentum p (due to the relativistic mass-increase which enhances that momentum at relativistic velocities). This relativistic correction, {gamma}2(dp/dt)2/m2 = {gamma}4(dv/dt)2 = {gamma}4a2, which is identical to Rabinowitz's relativistic correction to Larmor's formula. (Bridgman cites the source of his formula 11-3 as John David Jackson's Classical Electrodynamics, Wiley, New York, 2nd ed., 1975, pages 660-5.)

Because a bigger bomb releases more gamma radiation which causes the vertical Compton current, it is clear that the time taken for the vertical electron Compton current to be cancelled out by the conduction current (the return of mobile negative electrons to inert heavy positive ions of air molecules, caused by the radial electric field caused by the charge separation which attracts them back to the ions) gets longer for bigger bombs. At 10 km from a 1 Mt surface burst, it appears that the peak electric field should be -1,200 v/m at 0.5 microsecond (the negative sign comes from the fact that this is due to the Compton current, which is a net upward flow of electrons, i.e., equivalent to a downward flow of conventional electric current which is defined after Franklin as flowing from positive to negative not the other way around as really occurs) which rapidly drops to zero at 1.3 microseconds and is then followed by a reversed electric field peaking at +110 v/m at about 2 microseconds (the positive sign being due to this field being caused by the net flow of electrons downward, returning to ions).

In the case of a 1 Mt air burst in sea level air, the radiated electric field at 10 km range is much weaker because the EMP is due to the air density gradient, but it has the same general nature as for a surface burst, peaking first in the negative direction with -19 v/m at 0.75 microsecond due to the Compton current, followed by a positive peak of +23 v/m at 3 microseconds due to the conduction current (returning electrons).

There is some nuclear test data available in declassified preliminary shot reports on the U.S. Department of Energy Marshall Islands Historical Documents database, giving some values for the radiated EMP electric field strengths measured for various Ivy (1952), Castle (1954) and Redwing (1956) Pacific nuclear tests, which can be compared to the theoretical predictions in DNA-EM-1:

King, 500 kt pure fission low air burst (451 m altitude): peak EMP at Maui (4200 km distance) = 1.0 v/m

Romeo, 11 Mt 64% fission surface burst: peak EMP at 320 km distance = 21 v/m

Koon, 110 kt 91% fission surface burst: peak EMP at 320 km distance = 15 v/m

Union, 6.9 Mt 72% fissin surface burst: peak EMP at 320 km distance = 40 v/m

Yankee, 13.5 Mt 52% fission surface burst: peak EMP at 320 km distance = 34 v/m

Nectar, 1.69 Mt 80% fission surface burst: peak EMP at 23 km distance = 775 v/m

Zuni, 3.53 Mt 15% fission surface burst: peak EMP at 334 km distance = 14.4 v/m

Flathead, 365 kt 73% fission surface burst: peak EMP at 343 km distance = 17.0 v/m; also the measured peak EMP at 525 km distance was 6.8 v/m

Osage, 1.7 kt 100% fission low air burst (204 m altitude): peak EMP at 13.5 km distance = 26 v/m

Seminole, 13.7 kt 80% fission burst inside a large water tank: peak EMP at 33.4 km distance = 0 v/m (no detectable EMP, due to the water blanket above the bomb in the water tank absorbing the nuclear radiation and preventing any effective EMP being generated)

The references for these data cited in the preliminary shot reports on that database are:

M.H. Olseon, Operation Castle, Project 7.1, Electromagnetic Radiation Calibration, weapon test report WT-930, June 1958, U.S. Armed Forces Special Weapons project, Secret-Restricted Data, and

Charles J. Ong, Analysis of Electromagnetic Pulse Produced by Nuclear Explosions, Operation Redwing, Project 6.5, 1956, Secret-Restricted Data.

The Dolan DNA-EM-1 manual chapter 7 is fairly accurate for Koon, Union, Yankee, and Nectar but generally over-estimates the peak electric field from these nuclear tests by about a factor of two, partly because the assessment of prompt gamma radiation output it uses is based on more efficient nuclear weapons with thinner casings than the 1950s test devices, and partly because at a distance of 320 km from a nuclear bomb there is some attenuation in the EMP radiation due to the ocean conductivity and the atomsphere, in addition to the purely geometrical effect of the inverse-of-distance fall off. The formula given by Dolan is probably only accurate within 50 km of a surface burst, and exaggerates the EMP at greater distances.

The main purpose of discussing the radiated EMP from a surface burst is, as already emphasised, not concerned with EMP damage but with the detection and identification of nuclear explosions by computerised radio receivers such as the British 'AWDREY' (atomic weapons detection, recognition, and estimation of yield) installations which have been developed since 1968 by the Atomic Weapons Establishment at Aldermaston and can automatically use the EMP to immediately detect and identify the characteristics of a nuclear explosion. To cover Britain, there were 13 AWDREY installations each with 75 miles operational range. The direction of the EMP measured by any two AWDREY's allowed the coordinates of the burst to be determined, while the time measured from the EMP radioflash to the final maximum pulse in the visible light flash of the explosion was used to accurately determine the total energy yield of the detonation. To discriminate against lightning and other false alarms, a detonation was only recorded by the instrument if there was both an EMP and a visible light flash with the nuclear explosion signature waveforms.


Similar systems are now installed in military satellites to detect and identify nuclear explosions, giving immediate warnings which can be used to predict the subsequent fallout hazard to be expected. Because the EMP differs substantially in a surface burst, an air burst, and a high altitude burst, the waveform of the EMP delivers some information on the type of burst as well as the fission and total yield. It also indicates the design of the bomb, since multi-staged thermonuclear weapons produce an EMP from each stage, although the secondary stage EMP is reduced to a known degree by the ionized conductivity of the air created by the primary stage. Therefore, EMP is a very useful signature of a nuclear explosion for delivering diagnostic information that can immediately be processed by suitably designed computer systems to be used for civil defence for predict fallout hazards downwind.

“In every listening radio set in the central Pacific came a loud click, caused by the electro-magnetic radiation... on Christmas Island John Challens heard the click and exclaimed jubilantly – ‘It worked!’” - Air Vice Marshal W. E. Oulton, nuclear test Task Force Commander, Christmas Island Cracker, Thomas Harmsworth, London, 1987, p. 326. (This was the 15 May 1957 EMP from British nuclear test Short Granite, 300 kt air burst at 2.2 km altitude.)

“At Christmas Island... the [radio] listeners heard the click of the radio-flash superimposed on the relay of Robert's commentary and sent word to London of another successful test.” - Air Vice Marshal W. E. Oulton, nuclear test Task Force Commander, Christmas Island Cracker, Thomas Harmsworth, London, 1987, p. 346. (This was the 31 May 1957 EMP from British nuclear test Orange Herald, a 700 kt air burst at 2.4 km altitude.)

On the effects of such EMP on radios, it's worth again referring to a study of radiated EMP effects on portable transistor radio receivers, made by A. D. Perryman of the U.K. Home Office Scientific Advisory Branch and published on page 25 of the originally 'Restricted' Home Office publication Fission Fragments, issue 21 (April 1977, edited by M. J. Thompson of the Home Office Emergency Services Division, Horseferry House, Dean Ryle Street, London):



'... SAB carried out a limited programme of tests in which four popular brands of transistor radio were exposed in an EMP simulator to threat-level pulses of electric field gradient about 50 kV/m. ... All these sets worked on dry cells [internal batteries] and had internal ferrite aerials for medium and long wave reception. In addition, sets 2, 3 and 4 had extendable whip aerials for VHF/FM reception. ...

'During the tests the receivers were first tuned to a well-known long-wave station and then subjected to a sequence of pulses in the EMP simulator. This test was repeated on the medium wave and VHF bands. Set 1 had no VHF facility and was therefore operated only on long and medium waves.

'The results of this experimentation showed that transistor radios of the type tested, when operated on long or medium waves, suffer little loss of performance. This could be attributed to the properties of the ferrite aerial and its associated circuitry (e.g. the relatively low coupling efficiency). Set 1 [the set with only a short internal ferrite rod aerial, and no long external extensible aerial], in fact, survived all the several pulses applied to it, whereas sets 2, 3 and 4 all failed soon after their whip aerials were extended for VHF reception. The cause of failure was identified as burnout of the transistors in the VHF RF [radio frequency] amplifier stage. Examination of these transistors under an electron microscope revealed deformation of their internal structure due to the passage of excessive current transients (estimated at up to 100 amps).

'Components other than transistors (e.g. capacitors, inductors, etc.) appeared to be unaffected...

'From this very limited test programme, transistor radios would appear to have a high probability of survival in a nuclear crisis when operated on long and medium bands using the internal ferrite aerial. If VHF ranges have to be used, then probably the safest mode of operation is with the whip aerial extended to the minimum length necessary to give just audible reception with the volume control fully up.'

This experiment indicates that battery operated transistor radio receivers working on internal ferrite rod antennas will be undamaged by EMP even in the worst case scenario (a high yield burst at high altitude giving on the order 50 kv/m peak radiated electric field). It was known from 1950s nuclear tests of course that vacuum tube/thermonic valve electronics in battery powered radios with short aerials were immune from EMP damage, but they work with higher power than most transistors so they can better withstand EMP. There is a clip of the broadcast live TV transmission of an early Nevada test on the DVD Trinity and Beyond which shows the very brief EMP interference on the transmitted signal from an electronic TV camera and transmitting station in a trench close to a nuclear detonation (there is a click on the audio and a brief loss of the transmitted video signal as you get when an analogue TV is not tuned to a transmitter). No permanent damage was produced in this old vacuum tube electronic equipment since it was relatively invulnerable and not connected to long conductors coming from the radiation deposition region of the explosion. Such self-contained battery-operated electronic equipment cannot be damaged by surface burst EMP beyond the blast damaged area of a nuclear explosion.

The long-range EMP damage threat from surface bursts, in other words, is essentially due not to battery operated items with short conductors, but is due to the pick-up in long conductors being channelled great distances by such conductors until finally entering mains-operated electronics and electrical systems, or equipment coupled to twisted pair telephone lines (not optical fibre, which is an insulator). The main problem from EMP will be the loss of mains electrical power. Laptop computers working on battery power with only the short internal wireless aerials for 802.11g microwave frequency networks (or for bluetooth networking) are unlikely to be damaged by the 1,000 v/m or lower order of magnitude of radiated EMP from any surface burst outside the blast damaged area. Even in the case of equipment connected to mains power, generally people will protect mains operated computers with power surge cutouts which can stop the natural EMP surges from nearby lightning bolts. The rise time of a transient in a long power cable is on the order of a microsecond or less, which is shorter than occurs with natural lightning, but modern power surge protectors are capable of providing protection against explosion EMP.

UPDATE ON HIGH ALTITUDE BURST EMP FIELD STRENGTH PREDICTIONS

An earlier post on this blog, 'EMP radiation from nuclear space bursts in 1962' (which has now been corrected and updated with the new information), documents the vital scientific data concerning high altitude nuclear test EMP from American and Russian nuclear tests in 1962 (and some previous tests in 1958 that were not properly measured due to a theory by Bethe that led to instruments being set up to detect a radiated EMP with the wrong polarization, duration and strength). That post still contains valuable data and the motivation for civil defence, although a great deal has changed and much new vital technical information on high altitude EMP predictions has come to light since that post was written.

Dr Conrad Longmire, as stated in that post, discovered the vital 'magnetic dipole' EMP mechanism for high altitude explosions (quite different to Bethe's 'electric dipole' predictions from 1958) after he saw Richard Wakefield's curve of EMP from the 9 July 1962 Starfish test of 1.4 Mt (1.4 kt of which was prompt gamma rays) at 400 km altitude.

'Longmire, a weapons designer who worked in [Los Alamos] T Division from 1949 to 1969 and currently is a Lab associate, played a key role in developing an understanding of some of the fundamental processes in weapons performance. His work included the original detailed theoretical analysis of boosting and ignition of the first thermonuclear device. Longmire ... wrote Elementary Plasma Physics (one of the early textbooks on this topic). He also became the first person to work out a detailed theory of the generation and propagation of the [high altitude magnetic dipole mechanism] electromagnetic pulse from nuclear weapons.'

Starfish was however not the first suitable measured curve of the magnetic dipole EMP, which was obtained from the 2 kt Yucca test in 1958 and described in detail in 1959 on page 347 of report ITR-1660-(SAN), but no EMP damage occurred from that test and so nobody worried about the size and shape of that EMP which was treated as an anomaly: 'Shot Yucca ... [EMP] field strength at Kusaie indicated that deflection at Wotho would have been some five times the scope limits... The wave form was radically different from that expected. The initial pulse was positive, instead of the usual negative. The signal consisted mostly of high frequencies of the order of 4 Mc, instead of the primary lower-frequency component [electric dipole EMP] normally received ...' Longmire's secret lectures on the magnetic dipole EMP mechanism were included in his April 1964 Los Alamos National Laboratory report, LAMS-3073. The first open publication of Longmire's theory was in the 1965 paper 'Detection of the Electromagnetic Radiation from Nuclear Explosions in Space' in the Physical Review (vol. 137B, p. 1369) by W. J. Karzas and Richard Latter of the RAND Corporation, which is available in RAND report format online as report AD0607788. (The same authors had perviously in October 1961 written a report on Bethe's misleading 'electric dipole' EMP mechanism - predicting incorrectly an EMP peak electric field of only 1 volt/metre at 400 km from a burst like Starfish instead of 50,000 volts/metre which occurs in the 'magnetic dipole' mechanism - called 'Electromagnetic Radiation from a Nuclear Explosion in Space', AD0412984.) It was only after the publication of this 1965 paper that the first real concerns about civil defence implications of high altitude bursts occurred.

The next paper which is widely cited in the open literature is Longmire's, 'On the electromagnetic pulse produced by nuclear explosions' published in the January 1978 issue of IEEE Transactions on Antennas and Propagation, volume 26, issue 1, pp. 3-13. That paper does not give the EMP field strength on the ground as a function of the high altitude burst yield and altitude, but it does give a useful discussion of the theoretical physics involved and also has a brief history of EMP. In the earlier post on this blog, I extracted the vital quantitative information from a March 1975 masters degree thesis by Louis W. Seiler, Jr., A Calculational Model for High Altitude EMP, AD-A009208, pages 33 and 36, which had gone unnoticed by everyone with an interest in the subject. I also obtained Richard Wakefield's EMP measurement from the Starfish test which is published in K. S. H. Lee's 1986 book, EMP Interaction, and added a scale to the plot using a declassified graph in Dolan's DNA-EM-1, Chapter 7. However, more recent information has now come to light.

The reason for checking these facts scientifically for civil defence is that the entire EMP problem will be dismissed by critics as a Pentagon invention for wasting time because of the alleged lack of EMP effects evidence or because of excessive secrecy being used as an excuse to not bother presenting the facts to the public in a scientific manner, with evidence for assertions ('extraordinary claims require extraordinary evidence' - Carl Sagan).

The latest information on EMP comes from a brand new (October 24, 2008) SUMMA Foundation database of EMP reports compiled by Dr Carl E. Baum of the Air Force Weapons Laboratory and hosted on the internet site of the Electrical and Computer Engineering Department of the University of New Mexico:

'Announcements. Update: Oct. 24, 2008 - We are pleased to announce that many of the unclassified Note Series are now on-line and is being hosted by the Electrical and Computer Engineering Department at the University of New Mexico. More notes will be added in the coming months. We appreciate your patience.'

The first of these reports that needs to be discussed here is Note 353 of March 1985 by Conrad L. Longmire, 'EMP on Honolulu from the Starfish Event'. Longmire notes that: 'the transverse component of the geomagnetic field, to which the EMP amplitude is approximately proportional, was only 0.23 Gauss. Over the northern U.S., for some rays, the transverse geomagnetic field is 2.5 times larger.' For Starfish he uses 400 km burst altitude, 1.4 Mt total yield and 1.4 kt (i.e. 0.1%) prompt gamma ray yield with a mean gamma ray energy of 2 MeV. Honolulu, Hawaii (which was 1,450 km from the Starfish bomb detonation point 400 km above Johnston Island) had a magnetic azimuth of 54.3 degrees East and a geomagnetic field strength in the source region of 0.35 gauss (the transverse component of this was 0.23 Gauss).

Longmire calculates that the peak radiated (transverse) EMP at Honolulu from Starfish was only 5,600 volts/metre at about 0.1 microsecond, with the EMP delivering 0.1 J/m2 of energy: 'The efficiency of conversion of gamma energy to EMP in this [Honolulu] direction is about 4.5 percent.' Longmire's vital Starfish EMP graph for Honolulu is shown below:
Longmire points out that much higher EMP fields occurred closer to the burst point, concluding on page 12: 'We see that the amplitude of the EMP incident on Honolulu [which blew the sturdy electric fuses in 1-3% of the streetlamps on the island] from the Starfish event was considerably smaller than could be produced over the northern U.S. ... Therefore one cannot conclude from what electrical and electronic damage did not occur in Honolulu that high-altitude EMP is not a serious threat.

'In addition, modern electronics is much more sensitive than that in common use in 1962. Strings of series-connected street lights did go out in Honolulu ... sensitive semiconductor components can easily be burned out by the EMP itself, 10-7 Joules being reportedly sufficient.'

The next vitally important report deserving discussion here in Dr Baum's collection is K. D. Leuthauser's A Complete EMP Environment Generated by High-Altitude Nuclear Bursts, Note 363, October 1992, which gives the following vital data (notice that 10 kt prompt gamma ray yield generally corresponds to a typical thermonuclear weapon yield of about 10 megatons):





Quotations from some of the Theoretical Notes on EMP in Dr Carl E. Baum's database:

Theoretical Note 368:

Conrad L. Longmire, Justification and verification of High-Altitude EMP Theory, Part 1, Mission Research Corporation, June 1986, pages 1-3:


'Over the 22 years since the first publication of the theory of High-Altitude Electromagnetic Pulse (HEMP), there have been several doubters of the correctness of that theory. ... commonly, it has been claimed that the HEMP is a much smaller pulse than our theory indicates and it has been implied, though not directly stated in writing, that the HEMP has been exaggerated by those who work on it in order to perpetuate their own employment. It could be noted that, in some quarters, the disparagement of HEMP has itself become an occupation. ...

'... One possible difficulty with previous papers is that they are based on solving Maxwell's equations. While this is the most legitimate approach for the mathematically inclined reader, many of the individuals we think it important to reach may not feel comfortable with that approach. We admit to being surprised at the number of people who have wanted to understand HEMP in terms of the fields radiated by individual Compton recoil electrons. Apparently our schools do a better job in teaching the applications of Maxwell's equations (in this case, the cyclotron radiation) than they do in imparting a basic understanding of those equations and how they work. ...

'The confidence we have in our calculations of the HEMP rests on two circumstances. The first of these is the basic simplicity of the theory. The physical processes involved, e.g., Compton scattering, are quite well known, and the physical parameters needed in the calculations, such as electron mobility, have been measured in relevant laboratory experiments. There is no mathematical difficulty in determining the solution of the outgoing wave equation, or in understanding why it is an accurate approximation. ...

'... the model of cycotron radiation from individual Compton recoil electrons is very difficult to apply with accuracy to our problem because of the multitudinous secondary electrons, which absorb the radiation emitted by the Compton electrons [preventing simple coherent addition of the individual fields from accelerated electrons once when the outgoing EMP wave front becomes strong, and therefore causing the radiated field to reach a saturation value in strong fields which is less than the simple summation of the individual electron contributions]. ...

'The other circumstance is that there is experimental data on the HEMP obtained by the Los Alamos Scientific Laboratory in the nuclear test series carried out in 1962. In a classified companion report (Mission Research Corp. report MRC-R-1037, November 1986) we present calculations of the HEMP from the Kingfish and Bluegill events and compare them with the experimental data. These calculations were performed some years ago, but they have not been widely circulated. In order to make the calculations transparently honest, the gamma-ray output was provided by Los Alamos, the HEMP calculations were performed by MRC and the comparison with the experimental data was made by RDA. The degree of agreement between calculation and experiment gives important verification of the correctness of HEMP theory.'

As stated in this blog post, Theoretical Note TN353 of March 1985 by Conrad L. Longmire, EMP on Honolulu from the Starfish Event calculates that the peak radiated (transverse) EMP at Honolulu from Starfish delivered only 0.1 J/m2 of energy: 'The efficiency of conversion of gamma energy to EMP in this [Honolulu] direction is about 4.5 percent.'

He and his collaborators elaborate on the causes of this inefficiency problem on page 24 of the January 1987 Theoretical Note TN354:

'Contributing to inefficiency ... only about half of the gamma energy is transferred to the Compton recoil electron, on the average [e.g., the mean 2 MeV prompt gamma rays create 1 MeV Compton electrons which in getting slowed down by hitting molecules each ionize 30,000 molecules releasing 30,000 'secondary' electrons, which uses up energy from the Compton electron that would otherwise be radiated as EMP energy; also, these 30,000 secondary electrons have random directions so they don't contribute to the Compton current, but they do contribute greatly to the rise in air conductivity, which helps to short-out the Compton current by allowing a return 'conduction current' of electrons to flow back to ions].'

Longmire also points out that Glasstone and Dolan's Effects of Nuclear Weapons pages 495 and 534 gives the fraction of bomb energy radiated in prompt gamma rays as 0.3 %. If this figure is correct, then 10 kt prompt gamma ray yield is obviously produced by a 3.3 megatons nuclear explosion. However, the Glasstone and Dolan figure of 0.3 % is apparently just the average of the 0.1 % to 0.5 % range specified by Dolan in Capabilities of Nuclear Weapons, Chapter 7, Electromagnetic Pulse (EMP) Phenomena, page 7-1 (Change 1, 1978 update):

'Briefly, the prompt gammas arise from the fission or fusion reactions taking place in the bomb and from the inelastic collisions of neutrons with the weapon materials. The fraction of the total weapon energy that may be contained in the prompt gammas will vary nominally from about 0.1% for high yield weapons to about 0.5% for low yield weapons, depending on weapon design and size. Special designs might increase the gamma fraction, whereas massive, inefficient designs would decrease it.'

UPDATES ON FALLOUT

Useful U.S. Naval Radiological Defense Laboratory nuclear test fallout information now available from the Journal of the Atmospheric Sciences as free PDF files:

CLOSE-IN FALLOUT
W. W. Kellogg, R. R. Rapp, and S. M. Greenfield
Journal of the Atmospheric Sciences Volume 14, Issue 1 (February 1957) pp. 1–8
[ PDF (655K) ]

ATMOSPHERIC REACTIONS OF SLURRY DROPLET FALLOUT
N. H. Farlow
Journal of the Atmospheric Sciences Volume 17, Issue 4 (August 1960) pp. 390–399
[ PDF (833K) ] This is a very important analysis for the situation of water surface bursts (see chapter 5 of Capabilities of Nuclear Weapons linked above for a detailed discussion of the formation and dose rates due to fallout in ocean water surface bursts) and shows clearly how the salt slurry fallout from ocean water surface bursts occurs: the water taken up in the cloud is frozen solid at high altitudes and partially evaporates as it falls through warmer layers of air near the ground while being deposited. Although sea water is 3.5 % salts by mass, the deposited fallout can contain much higher concentrations and even a slurry of salt crystals (if the salt concentration exceeds the saturation concentration of salt in water) due to evaporation of the water. This fallout contains relativity soluble ionic fission products which can soak in to surfaces and become chemically attached to molecules in contaminated materials, making subsequent decontamination efforts less effective than is the case with the insoluble glass spheres of fallout created by a land surface burst on silicate based soil. Such fallout needs to be removed from surfaces before it soaks in and dries off, such as by a continuous water spray (American ships at nuclear tests used their fire-hosing sprinkler systems on deck during fallout to prevent deposition of slurry fallout, which was washed down drains and off the decks as it landed).

A THEORY FOR CLOSE-IN FALLOUT FROM LAND-SURFACE NUCLEAR BURSTS
Albert D. Anderson
Journal of the Atmospheric Sciences Volume 18, Issue 4 (August 1961) pp. 431–442
[ PDF (1.03M) ]

Report Date : 27 MAY 1960
Reply
Albert D. Anderson
Journal of Applied Meteorology Volume 1, Issue 3 (September 1962) pp. 434–436
[ PDF (222K) ]

Larson, K. H. ; Neel, J. W. ; Hawthrone, H. A. ; Mork, H. M. ; Rowland, R . H., Distribution, Characteristics, and Biotic Availability of Fallout, Operation Plumbbob, CALIFORNIA UNIV LOS ANGELES LAB OF NUCLEAR MEDICINE AND RADIATION BIOLOGY, OCT 1957, 613 pp., ADA077509, 26.5 MB PDF file: http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA077509&Location=U2&doc=GetTRDoc.pdf

RAND Corporation 1950s fallout research, analyzing the rocket determination of radioactivity within the mushroom cloud from the 1956 Redwing-Zuni test (3.53 Mt surface burst, 15 % fission yield, Bikini Atoll): http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD337920&Location=U2&doc=GetTRDoc.pdf

The original AFSWP (U.S. Armed Forces Special Weapons Project) fallout model used in a simplified format in early editions of The Effects of Nuclear Weapons is D. C. Borg, et al., Radioactive Fall-Out Hazards From Surface Bursts of Very High Yield Nuclear Weapons, AFSWP-507, May 1954. This report uses the Mike fallout pattern for upwind and ground zero area fallout (of importance because this fallout covers the blast damaged area), but uses Bravo fallout data for the downwind fallout area. The yield scaling system is to scale both dose rates and distances by the cube-root of the total weapon power, and to scale dose rates directly in proportion to the fission yield fraction. For kiloton yields, The Effects of Nuclear Weapons used the Nevada Jangle-Sugar 1.2 kt burst fallout pattern as the basis for scaling fallout instead of the Mike and Bravo fallout patterns which were only used for megaton yields. Discussing this data and prediction system is controversial. On the one hand, the 1950s fallout pattern data is empirical scientific data that has not been superseded, so it is still valid. On the other hand, some would argue that computerized predictions of fallout provide a more "modern" and "sophisticated" basis for fallout predictions.

The Americans have also published online a declassified report with the fallout patterns from some British and French nuclear tests, ADA956123, which unfortunately does not contain the best data. There are far more useful declassified fallout patterns for the British Hurricane (1952), Totem (1953), Buffalo (1956) and Antler (1957) test series shots available in file series DEFE 16 and I think ADM 285/167 and ADM 285/169 at the U.K. National Archives in Kew. The most important fallout pattern is the Hurricane nuclear test since it was a very shallow underwater burst inside a ship. The American version is unclear:





Above: the fallout pattern version given to me for the British Hurricane 25 kt very shallow underwater test (exploded 2.7 m below the waterline inside the hull of HMS Plym a 1,370-ton River class frigate anchored in 12 m of water 350 m offshore, creating a saucer-shaped crater on the seabed 6 m deep and 300 m across), kindly supplied by Aldermaston in 1995 after it was declassified, compared to the American version.

U.S. Naval Radiological Defense Laboratory summary of fallout properties: http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD623485&Location=U2&doc=GetTRDoc.pdf (This is used on Glasstone and Dolan 1977 but unfortunately this report excludes classified data on which tests the fallout is from, so is non-quantitative and vague, and is also very sketchy in what it does present which is just a tiny example from extensive classified data, and by no means a good summary compared to reports by Dr Carl F. Miller and others, see for example http://glasstone.blogspot.com/2007/03/dr-carl-f-millers-fallout-and.html and other posts on this blog.)

Additionally, Dr Carl F. Miller's major report theoretically calculating the fractionation of fission products by fireball heat and the effect of this upon the fission product composition of fallout particles and therefore the decay rate of the fallout radiation downwind, AD0241240, 'A THEORY OF FORMATION OF FALLOUT FROM LAND-SURFACE NUCLEAR DETONATIONS AND DECAY OF THE FISSION PRODUCTS' (U.S. NAVAL RADIOLOGICAL DEFENSE LAB., SAN FRANCISCO), 27 May 1960, is now available from DTIC as a free PDF download at: http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD241240&Location=U2&doc=GetTRDoc.pdf

“The foliage making up the crowns [upper branches and leaves] of the trees, while it has a high probability of being exposed to the full free-field radiation environment from air bursts... may, however, materially reduce the exposure of the forest floor by generating quantities of smoke and steam, as well as by direct shading.” - Philip J. Dolan, Capabilities of Nuclear Weapons, U.S. Defense Nuclear Agency, 1978 revision, Secret – Restricted Data, Chapter 15, paragraph 15-9.

“Fuels seldom burn vigorously, regardless of the wind conditions, when fuel moisture content exceeds about 16 percent. This corresponds to an equilibrium moisture content for a condition of 80 percent relative humidity. Rainfall of only a fraction of an inch will render most fuels temporarily nonflammable and may extinguish fires in thin fuels... Surface fuels in the interior of timber stands are exposed to reduced wind velocities; generally, these fuels retain their moisture as a result of shielding from the wind and shading from sunlight by the canopy.” - Philip J. Dolan, Capabilities of Nuclear Weapons, U.S. Defense Nuclear Agency, 1978 revision, Secret – Restricted Data, Chapter 15, page 15-60.



The sixth Chinese nuclear test, their first Teller-Ulam (separate staged thermonuclear) design with a fusion-boosted U-235 primary and a U-238 pusher around the fusion stage, yielding 3.3 Mt on 17 June 1967. It was dropped from Hong-6 (Chinese manufactured Tu-16) and was parachute-retarded with detonation at 2,960 meters altitude:



"Bomb away!

"The hydrogen bomb gently falls toward the ground. It will be exploding 2900 meters above ground level.

"9, 8, 7, 6, 5, 4, 3, 2, 1, detonate!

"June 17th 1967, at 8:20am, our nation's first hydrogen bomb achieved success!

"A brightness appears by the fireball. It is indeed the sun.

"From the first atomic explosion to the first thermonuclear explosion, it took USA 7 years 3 months, took the Soviet Union 4 years, took the United Kingdom 4 years 7 months. Our nation worked just over 2 years to achieve the momentus leap from atomic to hydrogen.

"We now know in 1952, USA exploded a 65 ton, 3 story high apparatus. When the Soviet Union air dropped its first hydrogen bomb in 1953, the explosive force was 400 kilotons. Our nation during this test used a small size, low weight, megaton level bomb to destroy a designated target. This proves once again the Chinese people can do what foreigners can do, and we can do it better!

"Looking towards the enormous mushroom cloud rising into the sky, Marshal Lie exclaimed, three million tons, enough, that's quite enough!"


Above: stills from the film, showing the expanding fireball of the 3.3 Mt Chinese air burst 17 June 1967; the bomb vapour blobs from the casing and debris of the bomb itself initially overtake the slowly-expanding early X-ray sphere (which expands merely due to the diffusion of soft X-rays that only travel a small distance before being absorbed in cold air, and re-radiating), and splash against the back of the compressed air shock wave forming in the fireball, creating a very spectacular 'star filled universe' effect before disappearing as the front of the air shock wave becomes the radiating surface, and forms behind it an opaque shield of nitrogen dioxide which absorbs light radiation coming from the interior of the fireball. (Brode discusses this effect in the Annual Review of Nuclear Science, vol. 18, 1968.)


Update:

It is of interest that the RAND Corporation site list a 1958 paper co-authored by Nobel Laureate Murray Gell-Mann who was a consultant to the RAND Corporation in the 1950s:

The Electromagnetic Signal from Nuclear Explosions at Sea Level. D(L)-8668, 1958, Christy, R. F., Murray Gell-Mann

8 Comments:

At 6:54 pm, Blogger nige said...

For contrast to the American candour, most British information of importance to civil defence on the radiation, EMP, and blast wave effects of nuclear tests is still classified and withheld in the library of Aldermaston:

http://www.nationalarchives.gov.uk


British Atomic Weapons Research Establishment (AWRE) / Atomic Weapons Establishment (AWE) reports on radiation, EMP and blast wave civil defence results of nuclear tests which are listed publically at the UK National Archives catalogue but are actually not available due to being retained as classified documents under the provisions of Section 3 (4) of the Public Records Act 1958:


SECRET INITIAL NUCLEAR RADIATION DATA FROM BRITISH NUCLEAR TESTS AND RELATED RESEARCH:


ES 3/43 Study of the Dependence of the Immediate Gamma Dose on Distance and Time, Based on Information from British and American Sources up to the End of 1956 (1957). Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES 3/75 Nuclear radiation fields from typical weapons (1965). Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

SECRET EMP (RADIO-FLASH) DATA FROM BRITISH NUCLEAR TESTS AND RELATED RESEARCH:

ES 5/147 Operation BUFFALO nuclear tests: Interim report: measurements of radio-flash (1957), T10/57, Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES 4/337 Introduction to radio-flash diagnostic measurements (1959), Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES 10/1378 Further computations on the radio-flash from high-yield air bursts (1966). Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES 10/1225 Progress report on radio-flash computations (1965). Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES 5/206 Operation GRAPPLE: interim report radio-flash measurements (1958). Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES 12/496 US/UK agreement on the use of atomic energy for mutual defence. Information transmitted by UK. Radio flash: study of the isometric effect (1968). Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES 12/488 US/UK agreement on the use of atomic energy for mutual defence. Information transmitted by UK. Further computations of the effects of weapons asymmetry on the radio flash from low-yield air bursts (1966). Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES 5/341 Operation SUNBEAM [American Nevada Test Site nuclear tests at surface level in 1962]: radio flash report (1964). Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES 1/1103 INTERIM REPORT ON RADIO FLASH MEASUREMENTS ON OPERATION GRAPPLE (1957) Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES 1/1104 Radio flash from atomic explosions (1958). Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES 1/1105 Radio flash from atomic explosions: protection of missile launching equipment (1959) Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES 4/525 Radio flash waveforms (1962). Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES 4/1130 AWRE programs for computing the radio-flash from ground and atmospheric bursts (1969). Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES 4/548 Intensities, spectra and energies of the radio flash pulses at very short distances from two types of nuclear explosions (1962). Closed Or Retained Document, Open Description, Retained by Department under Section 3.4



SECRET BLAST WAVE DATA FROM BRITISH NUCLEAR TESTS:



ES12/0017 A Comparison of British Air Blast with Nuclear Weapons Blast Phenomena. Part 1 Introduction and Free Air Burst (1960) UK National Archives: Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES12/0018 A Comparison of British Air Blast with Nuclear Weapons Blast Phenomena. Part 2 NonIdeal (Precursor) Effects (1960) UK National Archives: Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES12/0019 A Comparison of British Air Blast with Nuclear Weapons Blast Phenomena. Part 3 The Variation of Air Blast on the Ground with Height of Burst (1960) UK National Archives: Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES 12/20 Comparison of British air blast with nuclear weapons blast phenomena: Part 4; variation of blast pressures in the air with height of burst; AWRE Foulness (1960) UK National Archives: Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES12/0021 A Comparison of British Air Blast with Nuclear Weapons Blast Phenomena (U) DASA 1200. Part 5 Air Blast from Surface Bursts. UK National Archives: Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

ES12/0022 COMPARISON OF BRITISH AIR BLAST WITH NUCLEAR WEAPONS BLAST PHENOMENA (U) (DASA 1200): Part 6 Tabulated UK Nuclear Data and Amended Figures from Parts 1 & 5. (1960) UK National Archives: Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

 
At 7:10 pm, Blogger nige said...

To avoid any possible confusion relating to the titles of the reports on blast waves above, the "Nuclear Weapons Blast Phenomena" is an American compendium of US nuclear test data on blast waves, report number DASA-1200. Nuclear Weapons Blast Phenomena, report DASA 1200, is the primary source for the blast data charts for both precursor and near ideal conditions in "Capabilities of Nuclear" and (in more simplified format) for Glasstone and Dolan 1977 (which omits the precusor type blast wave height-of-burst curves, and only gives data for nearly ideal conditions).

Therefore, "A Comparison of British Air Blast with Nuclear Weapons Blast Phenomena" is a comparison of British nuclear test blast wave data with American nuclear test blast wave data.

There is a published account of the differences between British and American height-of-burst curves from nuclear test data in the paper:

Lord Penney, D. E. J. Samuels, and G. C. Scorgie, “The Nuclear Explosive Yields at Hiroshima and Nagasaki,” Philosophical Transactions of the Royal Society of London, vol. 266, pp. 357-424 (1970).

That paper - while giving two sets of British height-of-burst overpressure curves for the UK nuclear testing programme, does not give the data points or test data (test name, yield and height of burst) used to derive the scaled smooth curves.

 
At 7:29 pm, Blogger nige said...

(With regard to EMP or "radioflash" - as known in the 1950s from the sharp click heard on radio receivers simultaneously with the visible light of the nuclear explosion - the Atomic Weapons Establishment has in fact openly released one semi-useful report on EMP to the UK National Archives for public viewing:

National Archives reference ES 4/361, original reference AWRE-O33/59 (1959), Theory of radioflash: Part 1; early phase of radioflash; Part 2; overall picture of of radioflash.

This report is unique in being mentioned in an unclassified history of the EMP by American EMP physicist Dr Conrad Longmire (who discovered the magnetic dipole EMP mechanism after looking at Richard Wakefield's measurement of the EMP waveform radiated by the Starfish test on 9 July 1962). Longmire mentioned the British report since it was apparently the earliest reliable theory of low-altitude burst EMP. This report gives one curve of the radiated EMP electromagnetic pulse measured 20 km away from an unspecified 1 kt low altitude British test detonation.)

 
At 1:41 am, Blogger nige said...

Concerning AWDREY, there is another retained document listed at the National Archives:

http://www.nationalarchives.gov.uk/catalogue/displaycataloguedetails.asp?CATLN=6&CATID=7698801

U.K. NATIONAL ARCHIVES REFERENCE: ES 4/1200

Records of the Atomic Weapons Establishment and predecessors

Atomic Weapons Research Establishment

"Operation of AWDREY during atomic weapon tests in the atmosphere", AWRE-O35/70, 1970

Availability: Closed Or Retained Document, Open Description, Retained by Department under Section 3.4

 
At 7:26 pm, Blogger nige said...

Another UK National Archives report of interest:

ADM 285/168

"Surface Phenomena at Operation Hurricane", 1956.

This is the same title as reference 1 (marked secret) in the American report http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA956123&Location=U2&doc=GetTRDoc.pdf

 
At 2:43 pm, Blogger nige said...

Nobel Laureate Hans A. Bethe's report containing the wrong EMP mechanism for high altitude bursts (electric dipole instead of magnetic dipole) is:

H. A. Bethe, "Electromagnetic Signal Expected from High-Altitude Test", Los Alamos Scientific Laboratory report LA-2173, October 1957, secret-restricted data.

This report is significant because it predicted all three major parameters so wrongly that it prevented the magnetic dipole EMP being discovered for five years. It predicted (1) totally the wrong polarization (the direction antenna need to be pointed to detect the EMP), (2) completely the wrong rise time of the EMP (the oscilloscope time-sweep setting needed to show up the pulse on the display so it could be photographed; the pulse duration is tens of nanoseconds not tens of microseconds), and finally (3) the wrong intensity of the pulse (about 1 volt/metre was predicted instead of 10,000 or more volts/metre, so the oscilloscope pulse height settings were wrong by a factor of 10,000 and any instruments which did detect the pulse just gave vertical spikes extending off-scale, with no information whatsoever about the peak EMP or its duration.

These problems were only resolved after one instrument operated in an instrumentation aircraft operated in 1962 by Wakefield at Starfish was set with a very fast sweep and low intensity, so it managed to capture the EMP peak and duration successfully:

Richard L. Wakefield, "Measurement of time interval from electromagnetic signal received in C-130 aircraft, 753 nautical miles from burst, at 11 degrees 16 minutes North, 115 degrees 7 minutes West, 24,750 feet", Los Alamos Scientific Laboratory, pages 44-45 of Francis Narin's Los Alamos Scientific Laboratory compilation "A 'Quick Look' at the Technical Results of Starfish Prime", report AD-A955411, August 1962. (Figure 8 on page 45 gives the Wakefield EMP waveform measurement for Starfish, and is headed "EM Time Interval Signal on C-130 aircraft 753 Nautical Miles from Burst".)

At subsequent 1962 "Fishbowl" (high altitude) tests Kingfish, Bluegill and Checkmate, similar oscilloscope settings were used to obtain further successful waveform measurements of EMP:

John S. Malik, "Dominic Fishbowl Radioflash Waveforms", Los Alamos Scientific Laboratory report LA(MS)-3105, May 1964, Secret-restricted data.

John S. Malik and Ralph E. Partridge, Jr., "Operation Dominic Radioflash Records", Los Alamos Scientific Laboratory report LAMS-3019, November 1963, Secret-restricted data.

The two reports above are still classified, more than 35 years after being written.

 
At 1:46 pm, Blogger nige said...

Update (26 Feb 2009): Vital fresh information on EMP from Starfish and other 1962 nuclear tests has been published and is reported on this blog in the new post:

http://glasstone.blogspot.com/2009/02/how-emp-turned-off-1-3-of-streetlamps.html

'The street lights on Ferdinand Street in Manoa and Kawainui Street in Kailua went out at the instant the bomb went off, according to several persons who called police last night.'

- HONOLULU ADVERTISER newspaper article dated 9 July 1962 (local time; reprinted in the Tuesday 21 February 1984 edition, celebrating the 15th anniversary of Hawaiian statehood to the U.S.A.).

At 11 pm on 8 July 1962 (local time, Hawaii), 300 streetlights in 30 series connected loops (strings) were fused by the EMP from the Starfish nuclear test, detonated 800 miles away and 248 miles above Johnston Island. This is approximately 1-3% of the total number of streetlights on Oahu.

In a much earlier blog post (linked here), the 1962 EMP damage effects from high altitude explosions (including three Russian high altitude tests of 300 kt each with differing altitudes of burst) were examined in some detail.

Then, in a more recent blog post (linked here), freshly released information from Dr Carl Baum's EMP notes series was given and discussed, including Dr Conrad Longmire's investigation (Note 353 of March 1985, EMP on Honolulu from the Starfish Event) which assessed the EMP field strength at Hawaii, which peaked after 100 nanoseconds at 5,600 volts/metre.

Longmire stated on page 12 of his report:

'We see that the amplitude of the EMP incident on Honolulu [which blew the sturdy electric fuses in 1-3% of the streetlamps on the island] from the Starfish event was considerably smaller than could be produced over the northern U.S. ... Therefore one cannot conclude from what electrical and electronic damage did not occur in Honolulu that high-altitude EMP is not a serious threat. In addition, modern electronics is much more sensitive than that in common use in 1962. Strings of series-connected street lights did go out in Honolulu ... sensitive semiconductor components can easily be burned out by the EMP itself, 10^(-7) Joules being reportedly sufficient.'

This 5,600 v/m figure allows definite correlations to be made between the observed effects and the size of the EMP field, which is a massive leap forward for quantitative civil defence assessments of the probable effects of EMP.

Now Dr Baum (who has an important and interesting overview of EMP here, although it misses out some early important pieces of the secret history of EMP in the table of historical developments) has made available the report by Charles N. Vittitoe, 'Did high-altitude EMP (electromagnetic pulse) cause the Hawaiian streetlight incident?', Sandia National Labs., Albuquerque, NM, report SAND-88-0043C; conference CONF-880852-1 (1988).

Vittitoe on page 3 states: 'Several damage effects have been attributed to the high-altitude EMP. Tesche notes the input-circuit troubles in radio receivers during the Starfish [1.4 Mt, 400 km altitude] and Checkmate [7 kt, 147 km altitude] bursts; the triggering of surge arresters on an airplane with a trailing-wire antenna during Starfish, Checkmate, and Bluegill [410 kt, 48 km altitude] ...'

This refers to the KC-135 aircraft that filmed the tests from above the clouds, approximately 300 kilometers away from the detonations.

The reference Vittitoe gives to Dr Frederick M. Tesche is: 'F. M. Tesche, IEEE Transactions on Power Delivery, PWRD-2, 1213 (1987). [This reference is unfortunately wrong since there were only 4 issues of that journal published in 1987 and page 1213 occurs in issue 4 - in the middle of an article on EMP by Dr Mario Rabinowitz - that article being also available on arXiv.org and reviewed critically in a previous blog post here.] The effects were reported earlier by G. S. Parks, Jr., T. I. Dayharsh, and A. L. Whitson, A Survey of EMP Effects During Operation Fishbowl, DASA [U.S. Department of Defense's Defense Atomic Support Agency, now the DTRA] Report DASA-2415, May 1970 (Secret - Restricted Data).'

Vittitoe then quotes Glasstone and Dolan's statement in The Effects of Nuclear Weapons:

'One of the best authenticated cases was the simultaneous failure of 30 strings (series-connected loops) of street lights at various locations on the Hawaiian
island of Oahu, at a distance of 800 miles from ground zero.'

The detonation occurred at 11pm 8 July 1962 (local time) for Hawaii, so the flash was seen across the night sky and the failure of some street lights was observed. Vittitoe usefully on page 5 quotes the vital newspaper reports of the EMP damage, the first of which is the most important since it was published the very next day following the explosion:

'The street lights on Ferdinand Street in Manoa and Kawainui Street in Kailua went out at the instant the bomb went off, according to several persons who called police last night.'

- HONOLULU ADVERTISER newspaper article dated 9 July 1962 (local time; this amazing Starfish EMP effects article was reprinted in the Tuesday 21 February 1984 edition, celebrating the 15th anniversary of Hawaiian statehood to the U.S.A.).

A technical investigation was then done by the streetlights department into the causes of the 300 streetlight failures, and then on 28 July 1962, the HONOLULU STAR-BULLETIN newspaper article 'What Happened on the Night of July 8?' by Robert Scott (a professor at Hawaii University) reported that a Honolulu streetlight department official attributed the failure of the streetlights to blown fuses, due to the energy released by the bomb test being coupled into the power supply line circuits (see illustration above; the street lamps were attached to regular overhead power line poles, allowing EMP energy to be coupled into the circuit).

On 8 April 1967, HONOLULU STAR-BULLETIN newspaper published an article by Cornelius Downes about the blown fuses: 'small black plastic rings with two discs of lead separated by thin, clear-plastic washers.'

Vittitoe reports that the streetlight officials found that: 'The failure of 30 strings was well beyond any expectations for severe [electrical lightning] storms (where ~4 failures were typical).'

Vittitoe then gives a full analysis of the physics of how the EMP calculated by Longmire turned off the streetlights, and confirms that the EMP was responsible for the fuse failures.

Interestingly, Vittitoe co-authoried the 2003 arXiv.org paper Radiative Reactions and Coherence Modeling in the High-Altitude Electromagnetic Pulse with Dr Mario Rabinowitz, who has kindly corresponded with me by email on the subjects of EMP and also particle physics (although Dr Rabinowitz did not mention this EMP paper he co-authored with Vittitoe!).

 
At 6:32 pm, Blogger nige said...

Concerning the early history of EMP as a damaging effect of nuclear weapons, a very brief and but pertinent discussion of EMP effects from low altitude and surface bursts occurs in the November 1957 edition of the Confidential (classified) U.S. Department of Defense, Armed Forces Special Weapons Project manual TM 23-200, “Capabilities of Atomic Weapons”, section 12, “Miscellaneous Radiation Damage Criteria”, page 12-2, paragraph 12.2c:

Electromagnetic Radiation. A large electrical signal is produced by a nuclear weapon detonation. The signal consists of a rather sharp transient signal with a strong frequency component in the neighborhood of 15 kilocycles. Field strengths greater than 1 volt per metre have been detected from megaton yield weapons at a distance of about 2,000 miles. Electronic equipment which responds to rapid, short duration transients can be expected to be actuated by pickup of this electrical noise.”

TM 23-200, “Capabilities of Atomic Weapons”, is a single volume consisting of 441 pages in 12 sections divided into 2 parts (it has only about a quarter as many pages as Dolan’s 1651 pages long 2-volume 1972 revision DNA-EM-1):

CONTENTS OF TM 23-200 "CAPABILITIES OF ATOMIC WEAPONS", NOVEMBER 1957, CONFIDENTIAL (declassified in 1997)

Preliminary pages, consisting of: title pages, distribution list, contents pages, page locator for physical phenomena figures and tables, and foreword (22 pages)

Part 1: Physical Phenomena

Section 1: Introduction (13 pages)
Section 2: Blast and Shock Phenomena (95 pages)
Section 3: Thermal Radiation Phenomena (19 pages)
Section 4: Nuclear Radiation Phenomena (87 pages)

Part 2: Damage Criteria

Section 5: Introduction (21 pages)
Section 6: Personnel Casualties (20 pages)
Section 7: Damage to Structures (54 pages)
Section 8: Damage to Naval Equipment (15 pages)
Section 9: Damage to Aircraft (11 pages)
Section 10: Damage to Military Field Equipment (23 pages)
Section 11: Forest Stands (15 pages)
Section 12: Miscellaneous Radiation Damage Criteria (10 pages)

Appendix 1: Supplementary Blast Data (32 pages)
Appendix 2: Useful Relationships (10 pages)
Appendix 3: Glossary (7 pages)
Appendix 4: Bibliography (9 pages) [Page 4 of this bibliography cites the report: J. F. Canu and P. J. Dolan, “Prediction of Neutron-Induced Activity in Soils”, AFSWP-518, June 1957, Secret – Restricted Data.]

It has a Foreword on page xxii by Edward N. Parker (Rear Admiral, USN), Chief, Armed Forces Special Weapons Project, stating:

“The purpose of this manual is to provide the military Services with a compendium of the phenomena manifested by the detonation of nuclear weapons and the effects thereof in terms of damage to targets of military interest.

“This edition of Capabilities of Atomic Weapons represents the continuing effort by the Armed Forces Special Weapons Project to make available the progressively improved data resulting from field testing, scaled tests, laboratory and theoretical analyses.

“... Every effort has been made to include the best available data which will assist the using Services in meeting their particular operational requirements. As additional or better data becomes available it will be incorporated herein.”

 

Post a Comment

<< Home