The effects of nuclear weapons. Credible nuclear deterrence, debunking "disarm or be annihilated". Realistic effects and credible nuclear weapon capabilities for deterring or stopping aggressive invasions and attacks which could escalate into major conventional or nuclear wars.

Wednesday, March 29, 2006

'Clean' nuclear weapon tests: Navajo and Zuni

Time magazine, Monday, Jul. 08, 1957

"Three of the nation's leading atomic scientists were ushered into the White House one morning last week by Atomic Energy Commission Chairman Lewis Strauss for a 45-minute conference with the President. The scientists: Edward Teller, credited with the theoretical discovery that led to a successful H-bomb, Ernest O. Lawrence, Nobel Prizewinning director of the University of California's radiation laboratory at Livermore, Calif., and Mark M. Mills, physicist and head of the lab's theoretical division. They brought a report of grave but potentially hopeful meaning. In the lab at Livermore, they told the President, scientists have found how to make H-bombs that will be 96% freer from radioactive fallout than the first models."

Above: clean-nuclear weapons physicist Dr Mark M. Mills testifying during his testimony before the Congressional Joint Atomic Energy Committee hearings on The Nature of Radioactive Fallout and Its Effects on Man, 1957 (the testimony is linked here in PDF format). Dr Mills was tragically killed in a helicopter accident during torrential rain on April 6, 1958, during the test preparations at Eniwetok Atoll, so the successful secret 1956 very "clean" test of the 4.5 Mt, 95% fusion, 5% fission Redwing-Navajo test was never publically demonstrated in the scheduled repeat Pinon test in 1958 (for comprehensive technical details of the Pinon, see Dr Gerald Johnson's 1958 Handbook for United Nations Observers, Pinon Test, Eniwetok, report UCRL-5367, PDF file linked here). After Dr Mills died, the public proof-testing of the clean bomb scheduled as Hardtack-Pinon was cancelled for weak reasons:

“[Lithium-7 deuteride and lithium-6 deuteride fusion fuel] costs can be estimated from the market price for lithium – with a lithium-6 content of 7.5 % - and with the advertised prices for heavy water [containing deuterium]. The latter sells for $28 per pound. ... the separation cost for lithium-6 ... should not be excessive since the isotopes Li-6 and Li-7 differ in mass by as much as 15 % and are therefore relatively easy to separate. My estimate for Li-6 D is $400 per pound. ... Making conservative assumptions about the fission yield in the [dirty U-238 fission] jacket, one concludes that a ton of TNT equivalent can be produced in the jacket for a fraction of one cent. ... It would undoubtedly be more expensive to construct a bomb without [a U-238 fission jacket]. And it would certainly be a much more difficult technical undertaking, since the success of Stage II [fusion of lithium deuteride] strongly depends upon the presence of the jacket. The neutron linkage and the cyclic nature of the multi-stage bomb make for a marriage between fission and fusion.”

- Dr Ralph E. Lapp, “The Humanitarian H-Bomb”, Bulletin of the Atomic Scientists, September 1956, p. 264.

Lapp's cynical complaint of the high relative cost of lithium-6 to U-238 in thermonuclear weapons ignores the fact that on average 50% of the yield of ordinary "dirty" stockpiled thermonuclear weapons comes from fusion anyway! By replacing the U-238 with lead, you're making no difference to the cost of the weapon: you're simply reducing the total yield and increasing the percentage due to fusion by a factor of 10 or more! In addition, Lapp ignores the fact that you simply don't need lithium-6 deuteride in a thermonuclear bomb: you can use natural lithium cheaply instead! In 1954, the highly efficient 15 Mt Castle-Bravo test used lithium only enriched to 40% lithium-6, while the successful 11 Mt Castle-Romeo test used only natural lithium deuteride (7.5% lithium-6 and 92.5% lithium-7), with no lithium enrichment. Sure, the heat released in the fission of the U-238 pusher by fusion neutrons acts as a catalyst to boost the fusion stage efficiency, and you lose that boost when you remove the U-238 jacket. But the successful tests of clean weapons prove that this is not an insuperable objection. Dr Samuel Glasstone, author of the secret nuclear weapon design physics report WASH-1037/8, 1962, 1963, 1972a and 1972b, wrote in his 1985 Funk & Wagnalls Encyclopedia (incorporated into Microsoft's Encarta 1998 multimedia encyclopedia) article on Nuclear Weapons:

"(E) Clean H Bombs

"On the average, about 50 percent of the power of an H-bomb results from thermonuclear-fusion reactions and the other 50 percent from fission that occurs in the A-bomb trigger and in the uranium jacket. A clean H-bomb is defined as one in which a significantly smaller proportion than 50 percent of the energy arises from fission. Because fusion does not produce any radioactive products directly, the fallout from a clean weapon is less than that from a normal or average H-bomb of the same total power. If an H-bomb were made with no uranium jacket but with a fission trigger, it would be relatively clean. Perhaps as little as 5 percent of the total explosive force might result from fission; the weapon would thus be 95 percent clean. The enhanced-radiation fusion bomb, also called the neutron bomb, which has been tested by the United States and other nuclear powers [1 kt, 500 metres altitude air burst] is considered a tactical weapon because it can do serious damage on the battlefield, penetrating tanks and other armored vehicles and causing death or serious injury to exposed individuals, without producing the radioactive fallout that endangers people or structures miles away."

Above: This newspaper article, "Clean H-Bomb Test Junked as U.S. Fears Mammoth Propaganda Dud", in The Deseret News, July 30, 1958, highlights the controversy in 1958 that fusion neutrons escaping into the atmosphere turn some nitrogen atoms into radioactive carbon-14, just as nuclear radiation from the sun does. But neutron-induced activities are a trivial hazard compared to the fission products from a "dirty" (high fission yield) surface burst. (See the declassified report USNRDL-TR-215, linked here, which contains the accurately measurements of the very small ratios of atoms/fission for neutron-induced Co-60 and other radionuclides in the 95% clean 1956 Navajo nuclear test fallout.) Another claim was that communist countries declined to attend the clean proof-test. But American could have still gone ahead and published the facts about clean nuclear weapons tests.

Above: neutron induced activities in atoms per fission depend upon bomb construction, particularly fission yield fraction ("cleanliness"). This table of data is based on the same source as Harold A. Knapp's 1960 table of accumulated doses from neutron induced activities in fallout (shown below), and is taken from the 1965 U.S. Naval Radiological Defense Laboratory report USNRDL-TR-1009 by Drs. Glenn R. Crocker and T. Turner. (This report is available as a 10 MB PDF download here. For Crocker's report on the fission product decay chains, see this link.)

Above: neutron induced activity gamma doses are smaller than fission product gamma doses, so "clean" nuclear weapons - despite releasing neutrons and creating some neutron induced activity - do eliminate much of the fallout problem.

Above: fallout from 95% 'clean' bomb test Navajo, Bikini Atoll, 1956 (WT-1317 ). Surface burst in the lagoon on a barge, the yield was 4.5 Mt, and it was only 5% fission. Each square in this and the next map has side of 20 minutes of latitude/longitude (= 20 nautical miles or 37 km). The radiation levels are relatively low, 20 times smaller than a fission weapon of similar yield.

Above is the best fallout pattern (from U.S. weapon test report WT-1317 by Drs. Terry Triffet and Philip D. LaRiviere) from the Zuni shot of 3.53 megatons, 15% fission at Bikini Atoll in 1956. It combines all available data, unlike the data in report DASA-1251, which gives unjoined data for the lagoon and the ocean. The ocean data was obtained in three ways, since fallout sinks in water. First, ships lowered probes into the water and measured the rate the fallout sank with time. Second, ships took samples of water from various depths for analysis. Third, the low level of radiation over the ocean was measured by both ships and aircraft, correcting for altitude and shielding of the geiger counter.

This particular test is unusual, as it was a surface burst on land (coral island), and was extensively studied; they even fired rockets through the different parts of the cloud at 7 and 15 minutes after burst, containing miniature radiation meters and radio transmitters, to map out the radioactivity distribution (it worked, showing toroidal distribution!). Ships were located in the fallout area at various locations to determine the fallout arrival time, build up rate (which was slow, due to the huge mushroom cloud which took time to pass overhead and diffused lengthways), decay rate after fallout arrival, mass of fallout and visibility of fallout deposit, and the chemical abundances of the various nuclides in fallout at different locations. Near the burst, large fallout particles arrive which fallout of the fireball before gaseous nuclides in decay chains have decayed into solids and condensed, so the biggest fallout particles, near ground zero, have relatively little I-131, Cs-137, and Sr-90. Gaseous precursors like xenon and krypton prevent Cs and Sr decay chains from condensing early, while iodine is volatile itself. Smaller fallout particles, while posing an overall smaller radiation hazard, have relatively more of these internal hazards (I-131 concentrates in the thyroid gland if ingested, say by drinking milk, while Cs-137 goes into muscle and Sr-90 goes into bone, assuming it is in a soluble form, which is of course not the case if the ground burst is on silicate-based soil, because the radioactivity is then trapped inside glass spheroids).

Here is a report of Dr. Hans A. Bethe, working group chairman, originally 'Top Secret - Restricted Data', to the President's Science Advisory Committee, dated 28 March 1958, defending 'clean nuclear weapons tests', courtesy of Uncle Sam:

Pages 8-9 defend clean nuclear weapons! As stated, Zuni was only 15% fission, so it was 85% clean. The dose rates given on these fallout patterns are extrapolated back to 1 hour, before the fallout had completely arrived anywhere, so are far higher than ever occurred anywhere! The true dose rates are lower due to decay during wind-carried transit. The dose rates also refer to the equivalent levels on land, which are about 535 times higher than over ocean at 2 days after burst, because the fallout landing on the ocean sinks steadily, and the water shields most of the radiation. The average decay rate of the fallout was t^-1.2 for all weapons tests. It is amazing how much secrecy there was during the cold war over thecivil defence data in WT-1317. The point is, fallout is not as bad as some people think, just like blast and cratering.

Co-60 bomb research

Wikipedia insert: Extensive residual radioactivity experiments and civil defence fallout studies were made during these tests. The Antler-1 test contained normal cobalt-59 which upon neutron capture was transmuted into radioactive cobalt-60 [1]. This provided a way to measure the neutron flux inside the weapon, although it was also of interest from the point of view of radiological warfare.

The then Science Editor of the New York Times, William L. Laurence, wrote in his 1959 book Men and Atoms (Simon & Schuster, New York, p. 195):

‘Because the cobalt bomb could be exploded from an unmanned barge in the middle of the ocean it could be made of any weight desired ... Professor Szilard has estimated that 400 one-ton deuterium-cobalt bombs would release enough radioactivity to extinguish all life on earth.’

The total amount of gamma ray energy emitted from cobalt-60 is only 2.82 MeV and this meagre energy release is spread over a statistical mean time of 1.44 times the 5.3 years half life of cobalt-60. (The number 1.44 is given approximately by 1 over the natural logarithm, i.e., the log to the base e, of 2, since this is the conversion factor between half-life and mean life time for radioactivity.) For comparison, every neutron used to fission an atom of U235, Pu239, or U238 releases 200 MeV of energy, including 30 MeV of residual radioactivity.

Hence, fission is by far the most efficient way to create radioactive contamination. The dose rate from Co-60 in the Antler-1 fallout was insignificant until most of the fission products had decayed, and only a few large pellets of Co-60 were found afterwards. The overall contribution of Co-60 to the fallout radiation was trivial compared to fission products and shorter-lived neutron induced activities in the bomb materials.

A study was done into the penetration of the fallout gamma radiation from the Antler tests by British Home Office and Atomic Weapons Research Establishment scientists A. M. Western and H. H. Collin in Maralinga. The results in their AWRE paper Operation Antler: the attenuation of residual radiation by structures, were published in Fission Fragments No. 10, June 1967, and showed the the long-term integrated fallout gamma radiation doses were reduced by a factor of 5 for a mass shielding of 312.4 kg per square metre, which is equivalent to a thickness of 15 cm of earth. A mass shielding of 781.1 kg per square metre stopped 96.6 % of the gamma rays, and this is equivalent to a protection factor of more than 29 by a shield of 38 cm of earth. America also performed studies which showed how fallout problems can be avoided.

Additional information:


Dr Terry Triffet and Philip D. LaRiviere, Operation Redwing, Project 2.63, Characterization of Fallout, U.S. Naval Radiological Defense Laboratory, 1961, Secret – Restricted Data, weapon test report WT-1317, Table B.22: some 21 radioactive isotopes of 19 different radioactive decay chains from neutron induced activity are reported for megaton range tests Navajo (lead pusher, 5 % fission), Zuni (lead pusher, 15 % fission) and Tewa (U-238 pusher, 87 % fission) are reported. Summing all the 19 separate decay chains abundances (of radioactive capture atoms per fission) gives results of:

15.6 atoms/fission for Navajo (5 % fission),

7.03 atoms/fission for Zuni (15 % fission), and

1.25 atoms/fission for Tewa (87 % fission).

(These data are computed from a full table which includes some nuclides not listed in WT-1317. I'll give that complete listing later. At present data tables do not seem to format properly on this blog site.)

But even for a very 'clean' bomb like Navajo, fission products dominate the fallout radiation dose. The sodium isotope Na-24 (15 hours half life) is generally considered the most important environmental form of neutron induced activity, and the abundance of Na-24 was only 0.0314 atom/fission in Navajo, 0.0109 atom/fission in Zuni, and 0.00284 atom/fission in Tewa. (These tests all involved large quantities of sea water being irradiated, Navajo and Tewa were water surface bursts and Zuni was on a small island surrounded by ocean.)

Far more important were U/Np-239, -240 and U-237 (which is created by a reaction whereby one neutron capture in U-238 results in two neutrons being emitted). The capture atoms/fission for Navajo, Zuni and Tewa were respectively 0.04, 0.31 and 0.36 for U/Np-239, 0.09, 0.005, and 0.09 for U/Np-240, and 0.09, 0.20 and 0.20 for U-237. (See also USNRDL-466.) These can emit as much radiation as fission products at the intensely critical early times of 20 hours to 2 weeks after detonation. They emit very low energy gamma rays, so the average energy of fallout gamma rays for a bomb containing a lot of U238 is low during the sheltering period, 0.2-0.6 MeV, and this allows efficient shielding to be done far more easily than implied by most civil defence calculations (which are based on gamma radiation from fission products with mean gamma energy of 0.7-1 MeV).

This was first pointed out based on British nuclear test fallout data (for Operation Totem and other tests) by George R. Stanbury in a Restricted U.K. Home Office Scientific Advisory Branch report in 1959, The contribution of U239 and Np239 to the radiation from fallout (although this paper originally contained a few calculation errors, the point that the average fallout gamma ray energy is lower than for fission products stands). You get much better shielding in a building that American calculations show, due to their incorrect use of 0.7-1 MeV mean gamma ray energy. The mean gamma ray energy at 8 days after Castle tests was only 0.34 MeV (WT-934 page 56, and WT-915 page 145; see also WT-917 pages 114-116, and also see of course WT-1317).

When tritium fuses with deuterium to produce helium-4 plus a neutron, the neutron’s mass is 20% of the total product mass, so the complete fusion of a 1 kg mixture of deuterium and tritium yields 0.2 kg of free neutrons, which – if all could be captured by cobalt-59 – would create 12 kg of Co-60. This was Professor Szilard’s basis for a ‘doomsday’ device.

However, Dr Gordon M. Dunning (b. 1910) of the U.S. Atomic Energy Commission, who was responsible for radiological safety during 1950s American tests, published calculations for such ‘cobalt-60 bombs’ (Health Physics, Vol. 4, 1960, p. 52). These show that a 100 megaton bomb with a thick cobalt-59 case, burst at a latitude of 45 degrees North, would produce an average Co-60 infinite-time gamma radiation exposure outdoors of 17 Roentgens in the band between 30 and 60 degrees North, around the earth. This ignores weathering of fallout, and assumes a uniform deposition.

The maximum rate at which this exposure would be received (outdoors), is 0.00025 Roentgens per hour, only 12 times greater than background radiation. Choosing a longer half-life reduces the intensity by increasing the time lapse between each particle emission; so the longer the half-life, the lower the intensity. If it is decaying rapidly, you can shelter while it decays. If the half-life is long, you can decontaminate the area before receiving a significant dose. No problem!

Creating Co-60 inside a weapon uses up precious neutrons, without releasing any prompt energy to help the nuclear fusion process, unlike U-238 fission, which releases both prompt energy and neutrons. Every neutron captured by Co-59 to produce radioactive Co-60 will lead to the release of only 2.82 MeV of radiation energy (one beta decay and two gamma rays). However, every neutron induced fission of uranium-238 releases about 200 MeV of energy, including more residual radiation energy than that released from Co-60. Therefore, fission gives a greater hazard than that from Co-6o and other neutron capture activities.

All of the escaping neutrons in an underwater or underground burst are captured in the water or soil, but only about 50% are captured by the water or soil in a surface burst. The amounts of neutron induced activity from the environment generally have a small effect, the highest activity being due to Na-24. In bombs containing U-238, the major neutron capture nuclides are Np-239 and U-237, which give off low energy gamma rays for the first few days and weeks. Shielding this radiation is easy.

The use of tungsten (W) carbide ‘pushers’ for clean nuclear weapons led to the discovery of W-185 (74 days half-life) in fallout from the 330 kt Yellowwood water surface burst at Eniwetok, 26 May 1958. It emits very low energy (0.055 MeV) gamma rays. Yellowwood produced 0.32 atoms of W-185 per fission, based on the ratio of W-185 to Zr-95 (assuming 0.048 atoms of Zr-95 per fission) in the crater sludge at 10 days after burst. (Frank G. Lowman, et al., U.S. Atomic Energy Commission report UWFL-57, 1959, p. 21.) W-185 was discovered on plankton and plant leaves, but was not taken up by the sea or land food chains. In fallout from the 104 kt, 30% fission Sedan shot at Nevada on 6 July 1962, W-187 (24 hours half-life) gave 55% of the gamma dose rate at 24 hours after burst, compared with 2% from Na-24 due to neutron capture in soil.

The ocean food-chain concentrates the neutron-capture nuclides iron (Fe) and zinc (Zn) to the extent that Fe-55 and Zn-65 constituted the only significant radioactivity dangers in clams, fish and birds which ate the fish after nuclear tests at Bikini and Eniwetok Atolls, during the 1950s. However, these nuclides are not concentrated in land vegetation, where the fission products cesium (which is similar to potassium) and strontium (which is similar to calcium) are of major importance. This is caused by the difference between the chemical composition of sea water and land. (Where necessary chemical elements are abundant, uptake of the chemically similar radioactive nuclide is greatly reduced by dilution.)

Fish caught at Eniwetok Atoll, a month after the 1.69 Mt Nectar shot in 1954, had undetectably low levels of fission products, but high levels of Fe-55 (95% of activity), Zn-65 (3.1%), and cobalt isotopes. In terns (sea birds) at Bikini Atoll, Zn-65 contributed almost all of the radioactivity after both the 1954 and 1956 tests. Fe-55 gave off 73.5% of the radioactivity of a clam kidney collected in 1956 at Eniwetok, 74 days after the 1.85 Mt Apache shot; cobalt-57, -58, and –60 contributed 9.6, 9.2, and 1.8%, while all of the fission products only contributed 3.5%.

Fish collected at Bikini Atoll two months after the 1956 Redwing series which included Zuni, Navajo and Tewa, had undetectably low levels of fission products, but Zn-65 contributed 35-58% of the activity, Fe-55 contributed 15-56%, and cobalt gave the remainder. (Frank G. Lowman, et al., U.S. Atomic Energy Commission report UWFL-51, 1957.)

In 1958, W.J. Heiman of the U.S. Naval Radiological Defense Laboratory released data on the sodium-24 activity induced in sea water after an underwater nuclear explosion in which 50 % of the gamma radiation at 4 days after burst is due to Np-239. He found that Na-24 contributed a maximum of 7.11 % of the gamma radiation, at about 24 hours after burst (Journal of Colloid Science, Vol. 13, 1958, pp. 329-36).

Hence even in a water burst, Np-239 radiation is far more important than Na-24.

Perhaps the most important modification in the April 1962 edition of The Effects of Nuclear Weapons was the disclosure that the radioactive fallout from nuclear weapons contains substantial amounts of radioactive nuclides from neutron capture in U-238. This had been pointed out by scientist George Stanbury (who worked with data from nuclear tests, and had attended British nuclear tests to study the effects) of the British Home Office Scientific Advisory Branch in report A12/SA/RM 75, The Contribution of U239 and Np239 to the Radiation from Fallout, November 1959, Confidential (declassified only in June 1988). Both Mr Stanbury and The Effects of Nuclear Weapons 1962 found 40% of the gamma radiation dose rate from fallout is the typical peak contribution due to Neptunium-239 and other capture nuclides (e.g., U-237, which is formed by an important reaction whereby 1 neutron capture in U-238 is followed by 2 neutrons being released), which all emit very low energy gamma radiation, and are important between a few hours and a few weeks after burst, i.e., in the critical period for fallout sheltering.

Because of the low energy of the gamma rays from such neutron-capture elements, which are present in large quantities in both Trinity-type fission bombs (with U-238 tampers) and thermonuclear bombs like Mike and Bravo, the fallout is much easier to protect against than pure fission products (average gamma energy 0.7 MeV). However, The Effects of Nuclear Weapons, while admitting that up to 40% of the gamma radiation is from such nuclides, did not point out the effect on the gamma energy and radiation shielding issue, unlike Stanbury’s Confidential civil defence report. This discovery greatly stimulated the “Protect and Survive” civil defence advice given out in Britain for many years, although it was kept secret because the exact abundances of these bomb nuclides in fallout were dependent on the precise bomb designs, which were Top Secret for decades.


Scroll down for the table. There is an error with this blog system changing html tables by prefixing them with large unwanted empty spaces. I'll fix this issue when I have time.

Nuclides formed by neutron capture in the thermonuclear bomb, 189 metric tons steel barge (NAVAJO AND TEWA TESTS), and the surrounding sea water

Measured Bikini Atoll test data for thermonuclear weapon designs of various fission yields, and two types of fusion charge ‘pusher’*



Exposure rate at 1 hour after detonation, (R/hr)/(kt/mi2) per capture atom/fission. 3 ft height, ideal theory, Triffet 61.


4.50 Mt, 5% fission

Lead (Pb) pusher

Bomb mass = 6.80 metric tons


3.53 Mt, 15% fission

Lead (Pb) pusher

Bomb mass = 5.51 metric tons


5.01 Mt, 87% fission

Uranium-238 pusher

Bomb mass = 7.14 metric tons

Abundance of neutron induced nuclides in total fallout, atoms per fission:


15.0 hours






27.7 days






312 days






2.58 hours






2.73 years






44.5 days






271 days






70.9 days






5.27 years






12.7 hours






244 days






2.71 days






60.2 days






8.15 hours






115 days






2.17 days






6.75 days






23.5 minutes



U-239 ®
Np ®


U-239 ®
Np ®


U-239 ®
Np ®


2.35 days



14.1 hours

0 (no gamma rays)


U-240 ®
Np ®


U-240 ®
Np ®


U-240 ®
Np ®


7.22 minutes


Total amount of neutron induced activity (capture atoms per fission):

* Compiled from the data in: Dr Terry Triffet and Philip D. LaRiviere, Operation Redwing, Project 2.63, Characterization of Fallout, U.S. Naval Radiological Defense Laboratory, 1961, originally Secret – Restricted Data (now unclassified), weapon test report WT-1317, Table B.22 and Dr Carl F. Miller, U.S. Naval Radiological Defense Laboratory report USNRDL-466, 1961, Table 11 on page 41, originally Secret – Restricted Data (now unclassified). The ‘pusher’ absorbs initial x-ray energy and implodes, compressing the fusion charge. Data for Fe-55 is based on the ratios of Fe-55 to Fe-59 reported by Frank G. Lowman, et al., U.S. Atomic Energy Commission report UWFL-51 (1957), and H.G. Hicks, Lawrence Livermore National Laboratory report UCRL-53505 (1984), assuming that the neutron capture ratios in iron were similar for shots Apache and Tewa. Data for Zn-65 is based on the ratios of Zn-65 to Mn-54 reported by F.D. Jennings, Operation Redwing, Project 2.62a, Fallout Studies by Oceanographic Methods, report WT-1316, Secret – Restricted Data, 1961, pages 115 and 120.

** The Zuni device contained antimony (Sb), which boils at 1750 C and was fractionated in the fallout. This is the only fractionated neutron capture nuclide. The data shown are for unfractionated cloud samples: for the close-in fallout at Bikini Lagoon the abundances for Sb-122 and Sb-124 are 8.7 times smaller.

***Note that this is not the maximum exposure rate from Np-239 (at 1 hour after detonation it is still increasing because it is the decay product of U-239).

“The first objection to battlefield ER weapons is that they potentially lower the nuclear threshold because of their tactical utility. In the kind of potential strategic use suggested where these warheads would be held back as an ultimate countervalue weapon only to be employed when exchange had degenerated to the general level, this argument loses its force: the threshold would long since have been crossed before use of ER weapons is even contemplated. In the strategic context, it is rather possible to argue that such weapons raise the threshold by reinforcing the awful human consequences of nuclear exchange: the hostages recognize they are still (or once again) prisoners and, thus, certain victims.”

- Dr Donald M. Snow (Associate Professor of Political Science and Director of International Studies, University of Alabama), “Strategic Implications of Enhanced Radiation Weapons”, Air University Review, July-August 1979 issue (online version linked here).

“You published an article ‘Armour defuses the neutron bomb’ by John Harris and Andre Gsponer (13 March, p 44). To support their contention that the neutron bomb is of no military value against tanks, the authors make a number of statements about the effects of nuclear weapons. Most of these statements are false ... Do the authors not realise that at 280 metres the thermal fluence is about 20 calories per square centimetre – a level which would leave a good proportion of infantrymen, dressed for NBC conditions, fit to fight on? ... Perhaps they are unaware of the fact that a tank exposed to a nuclear burst with 30 times the blast output of their weapon, and at a range about 30 per cent greater than their 280 metres, was only moderately damaged, and was usable straight afterwards. ... we find that Harris and Gsponer’s conclusion that the ‘special effectiveness of the neutron bomb against tanks is illusory’ does not even stand up to this rather cursory scrutiny. They appear to be ignorant of the nature and effects of the blast and heat outputs of nuclear weapons, and unaware of the constraints under which the tank designer must operate.”

- C. S. Grace, Royal Military College of Science, Shrivenham, Wiltshire, New Scientist, 12 June 1986, p. 62.


At 1:05 pm, Anonymous Anonymous said...

How clean nuclear weapons led Dr Samuel T. Choen to invent the neutron bomb circa 1958:

Samuel Cohen
From Wikipedia

Samuel T. Cohen is a physicist who is known for inventing the W70 warhead, the "enhanced neutron weapon" or neutron bomb, the blueprints of which were allegedly stolen by the Chinese [1]. He got his physics PhD from UCLA. In 1944 he worked on the Manhattan project with calculating how neutrons behaved in Fat Man. At RAND Corporation in 1950, his calculations of the intensity of radiation from fallout were included as a special appendix in Samuel Glasstone's book The Effects of Atomic Weapons. In the Vietnam War, Cohen argued that using small neutron bombs would end the war quickly and save many American lives, but politicians were not amenable to his ideas. He was a member of the Los Alamos Tactical Nuclear Weapons Panel in the early 1970s. President Carter delayed the neutron bomb in 1978 [2], but during Reagan's presidency, Cohen claims to have convinced Reagan to make 700 neutron bombs, 350 shells to go into the 8 inch (200-millimetre) howitzer and 350 W70 warheads for the Lance missile [3]. Cohen's backing of investigations into these controversial ideas won him some media attention after many years of being ignored [4]. In 1992 he was featured on the award-winning BBC TV series Pandora's Box episode, To the Brink of Eternity, discussing his battles with officialdom and colleagues at the RAND Corporation.

'Clean' nuclear tests and Cohen's revolutionary invention
In 1956, President Eisenhower announced the testing of a 95% 'clean' (2-stage) fusion weapon, later identified to have been the 11 July Navajo test at Bikini Atoll during Operation Redwing. This weapon had a 4.5 megatons yield. Previous 'dirty' weapons had fission proportions of 50-77%, due to the use of uranium-238 as a 'pusher' around the lithium deuteride (secondary) stage. (The fusion neutrons have energies of up to 14.1 MeV, well exceeding the 1.1 MeV 'fission threshold' for U-238.) The 1956 'clean' tests used a lead pusher, while in 1958 a tungsten carbide pusher was employed. Hans A. Bethe supported clean nuclear weapons in 1958 as Chairman of a Presidential science advisory group on nuclear testing [5]:

"... certain hard targets require ground bursts, such as airfield runways if it is desired to make a crater, railroad yards if severe destruction of tracks is to be accomplished... The use of clean weapons in strategic situations may be indicated in order to protect the local population." (Dr Hans Bethe, 27 March 1958 Top Secret - Restricted Data Report to the NSC Ad Hoc Working Group on the Technical Feasibility of a Cessation of Nuclear Testing (Bethe was the Working Group Chairman, page 9).

In consequence of Bethe's recommendations, on 12 July 1958, the Hardtack-Poplar shot on a barge in the lagoon yielded 9.3 megatons, of which only 4.8% was fission. It was 95.2% clean. It was the clean Mk-41C warhead.

Cohen in 1958 investigated a low-yield 'clean' nuclear weapon and discovered that the 'clean' bomb case thickness scales as the cube-root of yield. So a larger percentage of neutrons escapes from a small detonation, due to the thinner case required to reflect back X-rays during the secondard stage (fusion) ignition. For example, a 1-kiloton bomb would need to have a case only 1/10th the thickness of that for 1-megaton [6].

This means that although most of the neutrons are absorbed by the outer casing in a 1-megaton bomb, in a 1-kiloton bomb they would mostly escape. A neutron bomb is only feasible if the yield is sufficiently high that efficient fusion stage ignition is possible, and if the yield is low enough that the case thickness will not absorb too many neutrons. This means that neutron bombs have a yield range of 1-10 kilotons, with fission proportion varying from 50% at 1-kiloton to 25% at 10-kilotons (all of which comes from the primary stage). The neutron output per kiloton is then approximately 10-15 times greater than for a pure fission implosion weapon or a standard (high yield) strategic warhead like a W87 or W88 [7].

Official U.S. Department of Defense manual on the neutron bomb
Cohen's neutron bomb is not mentioned in the unclassified manual by Glasstone and Dolan, The Effects of Nuclear Weapons 1957-77, but is included as an 'enhanced neutron weapon' in chapter 5 of the declassified (formerly secret) manual edited by Philip J. Dolan, Capabilities of Nuclear Weapons, U.S. Department of Defense, effects manual DNA-EM-1, updated 1981 (U.S. Freedom of Information Act).

Provided that the weapon was not used in a thunderstorm, no fallout effects would occur from the use of a neutron bomb according to that manual, as the combination of 500 m burst altitude and low yield prevents fallout in addition to significant thermal and blast effects. The reduction in damage outside the target area is a major advantage of such a weapon to deter massed tank invasions. An aggressor would thus be forced to disperse tanks, which would make them easier to destroy by simple hand-held anti-tank missile launchers.

Cohen stated that he "worked in France on low-yield, highly discriminate tactical nuclear weapons in 1979-1980".

"In 1979, Pope John Paul II conferred on one of the authors (Sam Cohen) a peace medal for his invention, the neutron bomb. This was a small nuclear weapon designed to do its work, killing enemy military forces, without destroying a country’s infrastructure." (Cohen, March 11, 2003)

The Pope, John Paul II, was from Poland and knew that Warsaw Pact forces had a massive tank superiority (though NATO maintained a technical superiority) in Europe and that a deterrent which was designed to minimise civilian casualties was a step away from indiscriminate warfare. Though the neutron bomb's killing by radiation is no different than chemical warfare.

The speed of modern warfare meant that the civilian population would be unlikely to withdraw from combat zones and would suffer a large number of deaths from even low yield nuclear weapons. The very deployment of the neutron bomb threatened an escalation to full scale nuclear retaliation, thus canceling out the supposed benefit of the neutron bomb. Advances in precision anti-tank weapons ultimately made the neutron bomb redundant.

In 1981, the Christian Science Monitor reported that there "are 19,500 tanks in the Soviet-controlled forces of the Warsaw Pact aimed at Western Europe. Of these, 12,500 are Soviet tanks in Soviet units. NATO has 7,000 tanks on its side facing the 19,500." (Joseph C. Harsch, "Neutron Bomb: Why It Worries The Russians," Christian Science Monitor, August 14, 1981, p. 1.) [8]

Hans A. Bethe, Working Group Chairman, originally Top Secret - Restricted Data Report of the the President's Science Advisory Committee, 28 March 1958, defending on pages 8-9 'clean nuclear weapons tests', online
Terry Triffet and Philip LaRiviere, Characterization of Fallout, Operation Redwing fallout studies, directly comparing contamination from two 'dirty' tests (Tewa and Flathead) to two 'clean' tests (Navajo and Zuni), online
Charles Platt, "Profits of Fear", August 16, 2005 online;
Sam Cohen and Joseph D. Douglass, Jr, "The Nuclear Threat That Doesn't Exist – or Does It?", March 11, 2003, online; Red mercury, fusion-only neutron bombs, Russia, Iraq, etc
---- "North Korea's Nuclear Initiative", April 28 2004 online
---- "Development of New Low-Yield Nuclear Weapons", March 9, 2003, online
---- "The Rogue Nuclear Threat", April 26, 2002, online
Joe Douglass, The Conflict Over Tactical Nuclear Weapons Policy in Europe (1968)
William R. Van Cleave, S. T. Cohen, Nuclear Weapons, Policies, and the Test Ban Issue, 1987, ISBN 0275923126
Samuel T. Cohen, We Can Prevent World War III, 1985, 2001, ISBN 0915463105
---- The Truth About the Neutron Bomb: The Inventor of the Bomb Speaks Out, William Morrow & Co., 1983, ISBN 0688016464
---- Shame: Confessions of the Father of the Neutron Bomb (2000), ISBN 0738822302, memoir
Review of Shame published on Amazon: [9]

At 1:42 pm, Blogger nige said...

copy of a comment:

The only paper by Hugh Everett I've ever read, back at the British Library in 1994, was "The Distribution and Effects of Fallout in Large Nuclear Weapon Campaigns",
Operations Research, Vol. 7, No. 2, 1959, pp. 226-248, It was complete trash even in 1959, I'm afraid to say.

He used the RAND Corporation fallout model for a start, which is based on nuclear tests at Bikini and Eniwetok where a large amount of sea water was incorporated into the fireball (the fireball in megaton surface burst events was always far large in diameter than the tiny test island or the barge in the lagoon). This led to a second hotspot on average 50-75 miles downwind (there was also one around ground zero) which the RAND model reproduced, but which was due to the salt water precipitating as salt crystals from the mushroom cloud. As the hydroscopic crystals fell through warm humid air layers, they gained weight from absorbing moisture, and became salt slurry particles which finally landed about 2-3 hours downwind in an irregular shaped hotspot. For a couple of examples of such fallout patterns at Bikini Atoll, see my post:

For another example, see

So I think Hugh Everett's fallout statistics are based on an implicit assumption that in a nuclear war the targets will be fought over pacific atolls in warm, humid locations.

His paper doesn't discuss any of this essential background, and is typical of the b******* calculations that abound on nuclear weapons effects.

At 3:02 pm, Blogger nige said...

The key declassified report by Dr Carl F. Miller is USNRDL-466, which since this post was written (which links to a copy of that report on a U.S. government run server), has been removed from the U.S. government document collection or the link has become corrupted. Hence the link in this post to USNRDL-466 does not work any longer.

An alternative server also hosts that crucial report by Dr Miller here:

Table 11 (on page 41 of the original document) contains all of the originally Secret - Restricted Data on neutron induced activities U-239/Np-239, U-237, and Np-240 in the fallout from 13 different key Jangle, Castle, Redwing and Plumbbob fallout producing tests.

Notice that i(1) on the top line of the table data is the reference 1 hour dose rate assuming 1 atom/fission, so that allows you to work out the atoms/fission ratios from the 1 hour dose rates given in that table.

E.g., the Sugar and Uncle shots of Jangle in 1951 both produced 1-hour reference dose rates of 0.106 units due to U-239, which itself would produce 0.1799 units if there was 1 atom/fission of U-239 produced.

Hence, Sugar and Uncle both produced 0.106/0.1799 = 0.59 atoms/fission of U-239 and Np-239 (ignore the data given in the table for Np-239 because that is for the actual Np-239 atoms per fission created by 1 hour, not the total Np-239; since Np-239 is created from the decay of U-239, the total amount of Mp-239 produced is identical to the amount of U-239 produced, but because U-239 has a half life of 23.5 minutes, only 83% of the Np-239 has actually been formed within 1 hour of detonation).

As the table shows, only thermonuclear weapons produce significant quantities of U-237.

It is also worthy of note that the fission bomb tests Diablo and Shasta of Plumbbob in 1957 both produced only 0.10 atom/fission of U-239/Np-239, which is only about one-sixth of the production in the 1951 Sugar and Uncle tests.

The reason is that the 1951 tests Sugar and Uncle were old-fashioned implosion bombs with thick U-238 neutron "reflectors" that (instead of simply reflecting neutrons back) captured a large proportion of neutrons emitted from the core, whereas the 1957 tests Diablo and Shasta did not employ U-238 as a thick neutron reflector. The smaller amounts of U-238 contained in Diablo and Shasta was present in the highly-enriched uranium that was used in the composite uranium-plutonium cores that were in use at that time.

Notice also that Castle-Bravo produced 0.56 atoms/fission of U-239/Np-239, 0.10 atoms/fission of U-237, and 0.14 atoms/fission of Np-240, according to Dr Miller's secret data.

Japanese investigators tried to measure the capture/fission ratios from the Castle-Bravo fallout that landed on the "Lucky Dragon No. 5" which was 100 miles downwind of the detonation (it was just north-west of Rongelap when fallout arrived).

To avoid secrecy, Dr Miller quoted the (unclassified) Japanese findings in his unclassified 1963 "Fallout and Radiological Countermeasures" SRI report and also in his 1964 SRI report "Biological and Radiological Effects of Fallout from Nuclear Explosions": the data from the Japanese physicists suggest a figure of 0.30 atoms/fission for U-239/Np-239 and 0.15 atoms/fission for U-237.

These figures are wrong: the first is too low and the second is too high. You can't chemically separate small quantities of these nuclides because they are quite similar chemically, so you can't distinguish the beta particles, only the gamma ray energies using a crystal and scintillation counter. The problem of accurate determination comes down to the quality of the equipment and the quality of the samples of the fallout. The fallout that had been subjected to spray and wind on the decks of the "Lucky Dragon No. 5" for two weeks on the voyage back to Japan was not idea, and nor was the calibration of the instruments which the Japanese physicists used.

The American data is far more reliable. In addition, the Japanese physicists did not know about fission product fractionation (see table 8 on page 35 of the declassified report by Dr Miller for fully corrected detailed fractionation data downwind from the Redwing 1956 tests), which reduced the accuracy of their determination of capture atoms/fission. This is because, in order to determine the number of say U-239 atoms/fission, you need to determine not only the number of U-239 atoms in your sample, but also the number of fissions. If you try to determine the number of fissions by measuring the number of Sr-90 atoms present and using the production ratio of Sr-90 on standard "M" shaped fission fragment abundance graphs, you will underestimate the number of fissions, because Sr-90 is depleted from local fallout due to the fireball temperature. The correct way to work out the amount of fission in a sample is to determine the number of atoms of something that is not fractionated, such as Nb-95 (the Americans originally in the 1950s used Mo-99 as the reference nuclide, switching to Nb-95 in the 1960s because it is more abundant in fallout, and is thus easier to measure with greater accuracy).

One other measurement of interest for the 1956 Redwing series is in the report by M. Morgenthau, H.E. Shaw, L.M. Hardin, R.C. Tomkins, and P.W. Krey, Preliminary Report, Operation Redwing, Project 2.65, Land Fallout Studies, U.S. Armed Forces Special Weapons Project, Sandia Base, Albuquerque, ITR-1319, January 1957: the Redwing-Lacrosse 40 kt test produced 0.2 atom/fission of Np-239.

In his 1959 report The Decontamination of Surfaces Contaminated with Fallout from Nuclear Detonations at Sea, U.S. Naval Radiological Defense laboratory, report USNRDL-TR-329, Dr Miller makes it clear that although Np-239 and U-237 can contrubute 50% of the gamma dose rate some days after a thermonuclear explosion, neutron induced activity from Na-24 in sea water is trivial by comparison.

Dr terry Triffet and Philip D. LaRiviere support this with detailed tables of neutron induced activity from a variety of different thermonuclear weapons (clean and dirty fission yields) tested during Operation Redwing in 1956, in their report Characterization of Fallout, weapon test report WT-1317 (1961):

At 10:37 am, Blogger nige said...

Table 11 (on page 41 of the Dr Miller's report USNRDL-466) allows the following product atom/fission ratios to be deduced:

J-Sugar: 0.59 atom/fission of U239

J-Uncle: 0.59 atom/fission of U239

C-Bravo: 0.56 atom/fission of U239, 0.10 atom/fission of U237, 0.14 atom/fission of U240

C-Romeo: 0.66 atom/fission of U239, 0.10 atom/fission of U237, 0.23 atom/fission of U240

C-Koon: 0.72 atom/fission of U239, 0.10 atom/fission of U237

C-Union: 0.44 atom/fission of U239, 0.20 atom/fission of U237, 0.07 atom/fission of U240

R-Zuni: 0.31 atom/fission of U239, 0.20 atom/fission of U237, 0.005 atom/fission of U240

R-Tewa: 0.36 atom/fission of U239, 0.20 atom/fission of U237, 0.09 atom/fission of U240

P-Diablo: 0.10 atom/fission of U239

P-Shasta: 0.10 atom/fission of U239

P-Coulomb C: 0.03 atom/fission of U239

The reason why Castle shot Union produced twice the ratio of U-237 atoms per fission that Bravo produced was that Union used a thermonuclear fuel consisting of lithium deuteride enriched to 95% lithium-6 and only 5% lithium-7, whereas Bravo used unenriched lithium deuteride, which contains only 7.42% lithium-6 and 92.58% lithium-7. Since lithium-6 is more readily fissioned by neutrons to produce tritium than lithium-7 is, the enriched lithium-6 in the Union bomb resulted in a higher ratio of tritium fusion reactions to deuterium fusion reactions than Bravo did. (Bravo did involve some tritium fusion, but the relative abundance of tritium in the Bravo bomb was somewhat lower than that in the Union bomb.) Consequently, Union produced more high-energy tritium fusion neutrons than Bravo did. Because U237 is only created in large quantities by high-energy neutrons, it is a sensitive indicator of the relative amount of energy derived from tritium fusion in a thermonuclear weapon. Deuterium fusion produces neutrons with lower energy than those produced in tritium fusion reactions. Therefore, the higher the amount ratio of tritium to deuterium produced in the bomb, the higher the production of U237.

Two deuterium atoms can fuse into helium-3, releasing a 2.4 MeV neutron. When tritium and deuterium fuse into helium-4, however, a 14.1 MeV neutron is emitted. (By conservation of momentum, the neutron takes most of the energy in fusion reactions. D + D -> He-3 + n results in the release of 3.2 MeV of energy, of which 75% is the kinetic energy of the neutron. T + D -> He-4 + n results in the release of 17.6 MeV of energy, of which 80% is the kinetic energy of the neutron.)

Quite a lot of other piecemeal data for other Redwing tests has also been declassified and released in other formerly secret reports.

WT-1317 page 65, table 3.14 states that Redwing-Flathead had a Np-239 product/fission ratio of 0.41 atom/fission.

As already stated in the previous comment, ITR-1319, implies that the Redwing-Lacrosse test produced 0.2 atom/fission of Np-239.

WT-1315 page 29, table 4.1 gives the relative activities from fission products and U239 at two times after burst for Redwing tests Cherokee, Zuni and Navajo. Because we already know that the absolute value of the ratio for Zuni is 0.31 atom/fission of U239 (from Dr Miller's report USNRDL-466, page 41, table 11), we can use WT-1315 page 29 table 4.1 to obtain the Np239 product/fission ratios from Cherokee and Navajo. As a result, we find that Cherokee produced 0.36 atoms/fission of Np239, while Navajo produced about 0.085 atom/fission of Np239.

(The Np-239 production shown for Navajo in the table of the main body of this blog post is incorrect.)

At 12:17 pm, Blogger nige said...

Regarding the clean neutron bomb controversy, the 1988 book by the late Chuck Hansen, U.S. Nuclear Weapons (Orion Books), gives some relevant information on pages 175-201:

"W-79 [this is the nuclear warhead of a rocket-propelled 8-inch diameter, 43-inch long, 215 pounds mass, artillery shell; this artillery shell includes a rocket motor to double the usual 8-inch shell's range to 18 miles, and has a target sensor and programmable height of burst as well as Category D PAL built into it to prevent unauthorised use]

"... Development engineering of the W-79 started at Livermore in January 1975. By 1976, the Army was developing a warhead for an eight-inch atomic artillery shell that would be the first U.S. weapon specially designed to reduce collateral damage from blast and radioactivity.

[Because 80% of the energy in tritium-deuterium fusion is released as 14.1 MeV (highly penetrating) neutrons, the blast and thermal output of the bomb is reduced and will be negligible for a 1kt neutron bomb burst at say 500 metres over the target, where only neutron radiation will be a hazard.]

"In January 1977, President Gerald Ford approved a Stockpile Memorandum that featured the W-79 as an 'enhanced radiation' weapon (the so-called 'neutron bomb which is really not much more than a boosted fission device). Production engineering began in March; this phase was suspended (for political reasons) at the end of September and not resumed until the beginning of November 1978.

[Actually, as Cohen has pointed out, the mechanism of the neutron bomb is that a standard Teller-Ulam design when reduced to very low yields automatically has a high neutron output. The case thickness, needed to reflect X-rays from the fission primary to the physically separate fusion charge within the weapon, is proportional to the cube-root of the total required yield of the weapon. So the case thickness required for a Teller-Ulam device of 1 kt is only 10% of that required for a total yield of 1 Mt. It is this massive, order-of-magnitude reduction of case thickness for a low-yield Teller-Ulam bomb, which makes the neutron bomb effect occur: the thin casing of a 1 kt Teller-Ulam allows over 90% of the neutrons to escape without being scattered and degraded to low energy, whereas the thick casing needed for a 1 Mt Teller-Ulam bomb results in something like 90% of the neutrons being captured or scattered and degraded to low energy.]

"The first production unit appeared in July 1981. Quantity production started in September and continued until August 1986 after 550 (including 325 'enhanced radiation' and 225 standard) W-79s were produced."

Hansen goes on to state that the W-79-1 model of the W-79 was the neutron bomb, which had a selectable yield of up to 2 kt: "the W-79-1 has three yields between a few hundred tons up to about two kilotons. Fission-fusion percentages range from 50:50 at the lower yield up to 25:75 at the higher yield."

The W-79-1 warhead is extremely small and the primary employs cylindrical implosion of Pu-239, instead of spherical implosion. I.e., the primary contains a core cylinder of Pu-239 which is surrounded by a beryllium neutron reflector and then a cylindrical shell of chemical high explosive.

This use of cylindrical implosion (not spherical implosion) for igniting fusion reactions was an old principle which was first tested in the Greenhouse-George nuclear test of 9 May 1951.

The reason of using a cylindrical primary is that the two ends of the fissioning plutonium rod in the centre are exposed and by placing a fusion charge nearby the exposed end, it is far easier to ignite fusion than in the case of a spherical implosion bomb where chemical high explosive has to first absorb then reradiate X-rays (which is a less efficient process because some energy is absorbed and used to create a shock wave instead of being passed on as X-rays, and the geometry - i.e. the bigger distance between the fusion charge and the fissioning material in the primary reduces the flux of radiation that hits the fusion charge).

Chuck Hansen's description claims that the fusion charge is a removable 'tritium reservoir' that is placed into a hollow area within the plutonium clinder of the fission primary, as in a boosted weapon. Actually, this is incorrect. In a cylindrical implosion weapon, unlike a spherical implosion weapon, fusion materials can be placed near the fissile material on the end of the plutonium cylinder, without taking up room within the cylinder itself: X-rays emitted by the end of the fissioning plutonium cylinder can then be used as in the Teller-Ulam configuration to do the necessary compression of the physically separated fusion fuel, which is a more efficient situation than 'boosting'.

Cylindrical implosion of the primary is required in a 2 kt neutron bomb artillery shell in order (1) to make the bomb fit into an artillery shell, and (2) to make the Teller-Ulam fusion system work efficiently at such low yields by eliminating the usual high explosive layer that is between the fissioning primary and the fusion charge if spherical implosion is used.

It is correct, however, that for efficient operation a very low yield neutron bomb of only 1 kt can utilise a fusion charge including a capsule of tritium gas (instead of just solid lithium-6 deuteride as is used in large thermonuclear weapons). This is not "boosting" as Chuck Hansen claimed, because the tritium is physically separated from the fission primary. The neutron bomb employs the Teller-Ulam concept. (It is not simply a boosted weapon, or the neutrons would be unable to escape easily.)

The W-66 warhead is another American neutron bomb, but the W-66 was for the "Sprint" ABM missile warhead: the neutrons would destroy incoming enemy ICBM warheads within the atmosphere (hence the need for low yield and no collateral damage, and the choice of using clean neutron bombs was ideal).

Theoretical research for the W-66 began with Samuel Cohen's work on the neutron bomb in 1958, but production engineering for the W-66 neutron bomb for the Sprint ABM warhead only began in January 1972, and the first W-66 warheads were manufactured in June 1974. By March 1975, 70 W-66 warheads had been produced.

The W-70 Mod 3 is another example of a neutron bomb. It was the warhead for the U.S. Army "Lance" missile.

Production engineering on the W-70 began in December 1970 and manufacture began in June 1973. By July 1977, 900 W-70s had been produced; these were ordinary thermonuclear warheads with selectable yields of up to 100 kt.

The development of the W-70 Mod 3, the neutron bomb version, began in April 1976 but was suspended by President Carter at the end of September 1977 for political reasons. Production engineering was resumed on 1 November 1978 and manufacture began in May 1981. From August 1981 to February 1983, 380 neutron bomb W-70 Mod 3 were built:

"Yield of the W-70 Mod 3 is selectable as one of two values: one slightly less than a kiloton and the other slightly in excess of a kiloton. Both yields are about 60% fusion and 40% fission." (Page 201 of Chuck Hansen's U.S. Nuclear Weapons, orion Books, 1988.)

The W-70 neutron bomb warhead is 465 pounds in mass, 97 inches long and 22 inches in diameter.

At 4:09 pm, Blogger nige said...

The link in a comment above to a post about Samuel Cohen's neutron bomb is defective.

The correct links are:

Also relevant (discusses natural nuclear "pollution" hysteria such as censorship from the popular media of all reports on the safe and complete containment of nuclear waste from the 15 Oklo nuclear reactors in the massive uranium ore seams of Gabon, Africa within sedimentary rock for the past 1,700 million years):

At 9:50 pm, Blogger nige said...

Dr Terry Triffet and Philip D. LaRiviere, Operation Redwing, Project 2.63, Characterization of Fallout, U.S. Naval Radiological Defense Laboratory, 1961, Secret – Restricted Data, weapon test report WT-1317, page 120:

"The induced products contributed 63 percent of the total dose rate in the Bikini Lagoon area 110 hours after Shot Zuni; and 65 percent of the dose rate from Shot Navajo products at an age of 301 days was due to induced products, mainly Mn-54 and Ta-182."

There is a page about Professor Triffet (who taught engineering at the University of Arizona after producing the 1961 weapon test report WT-1317, and died in 2003 from cancer at age 80), here.

At 3:34 pm, Blogger nige said...

Some information on the measured capture atoms/fissions ratios for cobalt isotopes in the clean (5% fission) 4.5 Mt Rewing-Navajo nuclear test have been published in the report:

P. O. Strom, J. L. Mackin, D. MacDonald, and P.E. Zigman, "LONG-LIVED COBALT ISOTOPES OBSERVED IN FALLOUT FROM THE NAVAJO DETONATION OF OPERATION REDWING", U.S. Naval Radiological Defense laboratory, technical report USNRDL-TR-215, 26 March 1958, originally classified Secret - Restricted Data.

Table 3 on page 7 states:

0.0088 Co-60 atoms/fission
0.0014 Co-57 atoms/fission
0.00074 Co-58 atoms/fission

At 1:45 pm, Blogger nige said...

With regard to the comment immediately above, it is interesting to note that the authors also wrote an unclassified report on the topic, published in the journal "Science" in 1958 (albeit without the specific nuclear test data references of the classified version of the report):

Peter O. Strom, James L. Mackin, Douglas MacDonald, and Paul E. Zigman, et al., "Long-lived cobalt isotopes observed in fallout", Science, vol. 128, August 22, issue number 3321, 1958, pp. 417-9.

This report notes that Co-60 is the most important gamma emitter in Redwing test fallout for the period of from 1-10 years after nuclear detonation. It also notes that the Co-60 originated from neutron capture in impurities in the weapon (i.e., the steel casing of the bomb and the steel barge that supported the bomb), because the amount of cobalt in the sea water around the detonation was far to small to account for the observed neutron-induced Co-60 activity.

Note that prior to the publication of Strom's report by Science in 1958, Science had earlier published a report by Shipman and others about the discovery of neutron-induced manganese-54 in fallout:

William H. Shipman, Philip Simone, and Herbert V. Weiss, "Detection of manganese-54 in radioactive fallout", Science, vol. 126, November 8, 1957, issue number 3280, pp. 971-2.

In addition, Drs. Ralph F. Palumbo and Frank G. Lowman reported on iron-55 (Fe-55) in fallout at Kabelle Island in Rongelap Atoll, in their report "The Occurrence of Antimony 125, Europium 155, Iron 55, and Other Radionuclides in Rongelap Atoll Soil", report UWFL-56, April 1958.

The neutron-induced iron-55, manganese-54 and cobalt-60 from neutron capture in the steel casing and delivery system around the bomb are major contributors - particularly at times around a year after detonation - to the fallout gamma dose rate in fractionated local fallout (depleted of Cs-137 due to its gaseous precursor in the hot fireball which prevents much of it condensing on the fast-falling large fallout particles which leave the fireball before it has cooled and condensed).

At 11:25 pm, Blogger nige said...

Some vital reports by Dr. Carl F. Miller:

Accession Number : AD0476572
Personal Author(s) : Miller, Carl F.

Handle / proxy Url :
Report Date : MAR 1964
Pagination or Media Count : 89
Abstract : Contents: The Nature of Fallout; Local Fallout; World-Wide Fallout; Potential Hazards from Fallout; Radioactive Decay; The Standard Intensity and Contour Properties. Formation of Fallout Particles; General Description of Fallout Formation Processes; The Structure and Composition of Individual Fallout Particles; Solubility Properties of Fallout; Radioactive Elements in Fallout; The Condensation Process.



The major purpose of this report is to outline and discuss these physical processes and the important parameters on which they depend.

Accession Number : AD0410522
Personal Author(s) : Miller, Carl F.
Handle / proxy Url :
Report Date : JAN 1963
Pagination or Media Count : 402

Abstract : The major purpose of this report is to outline and discuss these physical processes and the important parameters on which they depend. The data, data analyses, data correlation schemes, and discussions presented here are organized to emphasize size basic principles so that an appropriate methodology can be applied in evaluating the radiological consequences of nuclear war. An explosion of any kind, detonated near the surface of the earth, causes material to be thrown up or drawn into a chimney of hot rising gases and raised aloft. In a nuclear explosion, two important processes occur: (1) radioactive elements, which are produced and vaporized in the process, condense into or on this material; and (2) a large amount of non-radioactive material, rises thousands of feet into the air before the small particles begin to fall back. This permits the winds to scatter them over large areas of the earth's surface. Thus, when the particles reach the surface of the earth they are far from their place of origin and contain, within or on their surface, radioactive elements. Whether they are solid particles produced from soil minerals, or liquid (salt- containing) particles produced from sea water, they are called fallout. The composition of fallout can be described in terms of two or three components. One is the inactive carrier; this consists of the environmental material at the location of the detonation and is the major component in a near-surface detonation. The second component includes all the radioactive elements in the fallout.


Fallout and Radiological Countermeasures. Volume 2
Title : Fallout and Radiological Countermeasures. Volume 2. Corporate Author : STANFORD RESEARCH INST MENLO PARK CA. Personal Author(s) : Miller, Carl F.

Accession Number : AD0410521
Title : Fallout and Radiological Countermeasures. Volume 2
Personal Author(s) : Miller, Carl F.
Handle / proxy Url :
Report Date : JAN 1963
Pagination or Media Count : 290

At 12:19 am, Blogger nige said...

I've just found more information on neutron capture to fission ratios for U-237, Np-239 etc.

At the U.K. National Archives, category DEFE16, there is are reports containing declassified data for the Np-239 production by 1957 U.K. tests ANTLER (3 shots at Maralinga), all very low atoms/fission due to the absence of a thick U-238 tamper (presumably those shots used beryllium neutron reflectors instead of U-238). There was some variation in the exact figures due to the different bomb designs: ANTLER used U-235, Pu-235 and composite core. The U-235 core bomb was only of course enriched to say 93.5% U-235 so it contained 6.5% U-238 or so, which produced more U-237 and U/Np-239 than the pure plutonium core device. The design of each ANTLER device bomb core is unclassified and was published in 1987 in the book by official Atomic Weapons Establishment historial Laura Arnold, in her book "A Very Special Relationship", H.M. Stationery Office.

There is also data in a report on U-237 by Hanna of AWRE in the DEFE16 files at the U.K. National Archives for the two 1953 U.K. TOTEM tests at Emu Field, Australia, giving the U-237 production, which was low because they were pure fission shots. I don't have my notes handy but from memory I think the U-237 production was only 1/3,000 atom per fission. The higher production in thermonuclear weapons occurs due to the higher neutron energy you get from fusion neutrons (up to and including 14.7 MeV), which well exceeds the neutron threshold energy needed for the reaction:

U-238 + neutron -> U-237 + 2 neutrons.

Another source of data on U/Np-239 production in U.K. nuclear test fallout in atoms/fission is available in the U.K. National Archines in George R. Stanbury's Home Office civil defence report:

HO 226/75

British Home Office Scientific Advisory Branch in report A12/SA/RM 75, The Contribution of U239 and Np239 to the Radiation from Fallout, November 1959, Confidential (declassified only in June 1988).
This gives a collection of early U.K. test data. One error that I noticed in Stanbury's calculations is that he wrongly predicts the U-239 contribution at early times. Stanbury correctly uses the exponential decay law for a single nuclide in combination with the [time]^{-1.2} decay law of fallout composed of 200 nuclides, to deduce that a neutron induced activity contributes a maximum % to the fallout decay rate at a time equal to 1.2/(ln 2) = 1.2/0.693 = 1.73 times its half life. E.g., for U-239 with 23.5 minutes half life, it contributes a maximum % to fallout at 23.5*1.73 = 40 minutes after burst, and for Np-239 with 56 hours half life, the maximum % contribution to the fallout occurs at 4 days after burst. But Stanbury gets the formula wrong for the U-239 contribution, calculating 8% peak contribution at 40 minutes, which I found to be in error, although it is not an important error (Stanbury gets the correct figure of 40% peak contribution by Np-239 to the gamma radiation of fallout at 4 days after burst, however).

The new data I've just found is in the excellent and vital report on fallout effects from U.K. tests in Australia on the public health (which is worth study for the other information it contains on fallout in addition, and will be used to update blog posts here):

Keith N. Wise and John R. Moroney, Public Health Impact of Fallout from British Nuclear Weapons Tests in Australia, 1952-1957, Australian Radiation Laboratory, report ARL/TR105, ISSN 0157-1400, May 1992, pages 6-7:
"The production ratios in atoms per fission, suggested by Crocker and Turner (1965) for neutron-induced radionuclides in fallout, reflect a different generation of nuclear weapons from at least some of those included among the twelve tested by Britain in Australia some ten years earlier. For example, for low yield explosions, Crocker and Turner give neptunium [Np]-239 and uranium [U]-237 as the dominant induced radionuclides, with typical production ratios

" - neptunium-239: 0.018 atoms per fission, from neutron capture in uranium-238

" - uranium-237: 0.026 atoms per fission, from (n, 2n) on uranium-238.

"Whereas measurements on airborne debris from HURRICANE (Gale 1954b), TOTEM (T1 and T2: Gale 1954a) and BUFFALO (KITE: Marston 1957) give values of neptunium-239 atoms per fission two orders of magnitude higher [this is due to the historical weapon design change, from using U-238 tampers around the bomb core in early tests, to using beryllium neutron reflectors in place of U-238 tampers in later designs]. A more detailed comparison is made in Table 2.1.

"Table 2.1



"Crocker and Turner (1965) 0.018

"HURRICANE 0.6+/-0.1

"TOTEM-1 1.8 +/-0.2

"TOTEM-2 2.5 +/-0.3"


Glenn R. Crocker and T. Turner, Calculated activities, exposure rates, and gamma spectra for unfractionated fission products, U.S. Naval Radiological Defense Laboratory, report USNRDL-TR-1009 (1965).

Gale 1954a: H. J. Gale, Operation TOTEM. Radioactive sampling and analysis report. Atomic Weapons Research Establishment report T6/54, 1954.

Gale 1954b: H. J. Gale, Operation HURRICANE Group Reports (part 51). Measurements of the radioactivity of an airborne sample of the cloud collected at Broome, Western Australia. Atomic Weapons Research Establishment, report T89/54, 1954.

Marston 1957: H. R. Marston, The accumulation of radioactive iodine in the thyroids of grazing animals subsequent to atomic weapons tests. Unpublished manuscript, July 1957.

At 12:32 am, Blogger nige said...

"There is also data in a report on U-237 by Hanna of AWRE in the DEFE16 files at the U.K. National Archives for the two 1953 U.K. TOTEM tests at Emu Field, Australia, giving the U-237 production, which was low because they were pure fission shots. I don't have my notes handy but from memory I think the U-237 production was only 1/3,000 atom per fission."


U.K. National Archives: DEFE 16/411

Determination of U237 production in Operation Totem

by F. C. Hanna


Report No N/M 68

At 1:33 pm, Blogger nige said...

U-237 results from neutron capture in U-238 followed by double neutron emission, the n,2n reaction first discovered by Professor Kenjiro Kimura, who used this reaction to discover Uranium-237, and later found this isotope in the CASTLE-BRAVO fallout that landed on the Japanese fishing boat 'Lucky Dragon' on 1 March 1954.

At 8:37 pm, Anonymous Anonymous said...

Clean strategic weapons were already stockpiled.That was MK-36C(6 MT,96%fusion).Full-yield version of MK36 had a yieid 19 mt ,10mt-was false.


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