Correction of nuclear test fallout data errors in the declassified report DASA-1251

ABOVE: the upwind fallout from the 10.4 Mt 82 ton MIKE shot on Elugelab Island, Eniwetok, 1 November 1952, was the heavest ever measured - heavier than that measured upwind (in similar wind speed conditions) of far bigger tests in 1954 like BRAVO, ROMEO and YANKEE. Despite this, the Chairman of the U.S. Atomic Energy Commission, Gordon Dean, signed a report on 1 November 1952 sent to President Truman which stated: 'The shot island Elugelab is missing, and where it was there is now an underwater crater of some 1,500 yards in diameter. No significant fall-out of radioactive contamination occurred.' (For the fallout pattern, see: W. B. Heidt, Jr., et al., Nature, Intensity and Distribution of Fall-out from MIKE Shot, Operation IVY, WT-615, April 1953, Secret – Restricted Data.) The reason was originally thought to be due to the fact that MIKE was an island burst, while BRAVO was a reef burst and ROMEO and YANKEE were barge bursts, but MIKE fireball extended over the ocean (the island was far smaller than the crater size torn in the reef), so there was not really that much difference between MIKE and BRAVO fallout. In 1956 coral island burst ZUNI produced much less fallout upwind than MIKE had, allowing for yield differences. The heavy upwind fallout from MIKE was a crater ejecta/throwout feature specific to the heavy 82 ton bomb case shock cratering action: the steel casing caused most of the energy to go into the case shock instead of into X-ray emission as occurs in weapons of lighter casing (this initial energy partition effect was first pointed out by Dr Brode's 1968 article 'Review of Nuclear Weapons Effects', Annual Review of Nuclear Science, vol. 18, pp. 153-202, and the role of case shock in cratering phenomenology was first described in RAND memorandum RM-2600 in 1960), so MIKE created an exceptionally strong case shock, which was efficient in spreading radioactive debris deep into the cratered material. This was the mechanism by which 82 ton MIKE deposited a larger fraction of the detonation energy into the ground than occurs with lighter cased weapons of similar yield (they release more energy initially as X-rays which are inefficient at cratering ), thereby producing a vast cratering/ejecta/throwout action which immediately contaminated large chunks of ejecta and large particles of throwout, that gradually deposited the higher levels of upwind contamination than occurred in later tests of weapons with a lighter bomb casing:

'Apparently, the dirty stem [of MIKE shot] was due to the coral particles, debris, and water which were sucked high into the air. Around the base of the stem, there appeared to be a curtain of water which soon dropped back around the area where the island of Elugelab had been.' - Operation IVY, 1952, U.S. Defense Nuclear Agency report DNA 6036F, page 187.

This is important for civil defence, since the ground zero area fallout and upwind fallout determines how soon rescue work can commence after a surface burst in a populated area. The use of MIKE upwind fallout data exaggerates the upwind fallout threat from modern, lighter cased nuclear weapons. Reference: George R. Stanbury, Some recent information from the United States about fall-out from ground burst megaton weapons, British Home Office Scientific Advisers' Branch report CD/SA 87, December 1957, classified Confidential, now declassified and released to the U.K. National Archives as HO225/87.

Stanbury there compares the 5 Mt, 87% fission TEWA fallout pattern from a September 1957 paper by Dr Frank H. Shelton, Technical Director of the U.S. Armed Forces Special Weapons Project, Physical Aspects of Fall-Out, and the TEWA, FLATHEAD, NAVAJO and ZUNI fallout patterns given in Edward A. Schuert's U.S. Naval Radiological Defense Laboratory report USNRDL-TR-139, A Fallout Forecasting Technique with Results Obtained from the Eniwetok Proving Ground, to MIKE fallout data the Home Office received from America in early 1954 in exchange for the British HURRICANE test fallout pattern, and to BRAVO upwind fallout data.

Stanbury also compares all these data with the upwind fallout data in the June 1957 edition of The Effects of Nuclear Weapons, which was based on the MIKE data for upwind fallout. Stanbury concluded: 'We are forced, therefore, to conclude that the heavy upwind contamination for a wind speed of 15 miles per hour, which is deduced from Table 9.71 of Effects of Nuclear Weapons is incompatible with the presently accepted physical model of the explosion which explains the megaton trial data so well. For lower wind speeds, however, it is clear that contamination could extend further upwind; in the limiting case of still air some contamination could cover the whole area under the mushroom cloud ... Conversely, of course, higher winds would result in less upwind contamination; for example with a wind speed of 30 miles per hour it seems probable that only the largest particles (1000 microns) would fall upwind of ground zero and contamination would not extend outside the area of total destruction.' I cannot find Frank H. Shelton's 1957 AFSWP paper Physical Aspects of Fall-Out online so will reproduce here some of the quotations from it which Stanbury used:

'Fall-out from a detonation of the order of a megaton will begin to arrive on the ground over an area the order of the size of the visible cloud, almost like a blanket at about 15 to 20 minutes for a large yield surface burst on an island or presumably on land. Fall-out from a shot of the order of a megaton on a barge in water will begin to arrive at the surface at about 30-40 minutes [due to the smaller average particle sizes in water surface bursts]. ... The above fall-out is exclusive of the vicinity of the crater and throw-out. ... The radiation will build up on the ground under the cloud and reach a peak in about 100 minutes for a detonation of the order of a megaton.'

Stanbury comments upon Shelton's statement that, at distances downwind from megaton detonations, the time to peak fallout dose rate from time of arrival is about equal to the arrival time (a statement based on Philip D. LaRiviere's report, USNRDL-TR-137): 'At long ranges (greater than 50 miles) the phenomena are much more complex. In the size range from 250 down to about 75 microns [diameter], particles are increasingly affected by such factors as diffusion, wind shear, etc., and they are falling from an increasingly greater range of heights. All these statistical variations tend to increase the average time of deposition at any place roughly in proportion to the average time taken to travel the intervening distance.' Stanbury adds that the Americans gave Britain (in exchange for the British test fallout data) the fact that the dose rate at one hour after burst was 10 R/hour at 9 miles upwind in 1954, and he adds that Val Paterson (head of the U.S. Federal Civil Defense Administration in 1954) gave a figure of 50 R/hour at one hour after burst, 6 miles upwind.

‘The increased efficiency with which superweapons disperse radioactive materials is to some extent counter-acted by the delay in arrival of fallout from the high source cloud and the rapid rate of decay which occurs in the interim.’ – R.L. Stetson, E.A. Schuert, W.W. Perkins, T.H. Shirasawa, and H.K. Chan, Distribution and Intensity of Fallout, Operation Castle, Project 2.5a, U.S. Naval Radiological Defense Laboratory, weapon test report WT-915, January 1956, classified ‘Secret – Restricted Data’ (only 240 copies printed), p. 101.

ABOVE: the useful fallout data collected at hundreds of nuclear tests was classified Secret - Restricted Data during the cold war; only 78 copies of this 1972 U.S. Defense Nuclear Agency (U.S. Department of Defense) report DNA 1251F were printed, summarising nuclear testing local fallout chemistry (solubility, fission product fractionation and neutron induced activity composition) and measured radiation properties. It was not made widely available, and is still secret now (only the front pages and last pages of the report have been declassified, all of the pages containing fallout information are still secret). Only vague, misleading reports about fallout were published, which left people highly confused on the subject of whether fallout is visible or not, how soluble it is, amd so on, and therefore undermined civil defence countermeasures by falsely making the public believe that 'nothing is really known on the subject for certain', rather than the truth that 'the facts are known but are being deliberately withheld from civil defence public information for reasons of secrecy.' The declassified versions of the 1251 series of reports omitted vitally important, essential fallout data and so were worse than useless for civil defence because what little was published was filled with errors, for example:

ABOVE: the obvious errors in this official 1963 U.S. Department of Defense DASA-1251 fallout pattern (re-issued in 1979 as DASA-1251-EX without any corrections) for a 110 kt 91% fission coral land surface burst in 1954, Castle-Koon (otherwise known as Operation Castle-shot number 3). First of all, the East-West width of Bikini Atoll is shown to be 40 statute miles, when in fact it is only 27 statute miles. Because all the fallout readings on rafts inside the lagoon and on the islands depend on this scale, the fallout pattern above is completely misleading, but that has not stopped it from being used in numerous fallout prediction model comparisons over the past 45 years. Second, the contours shown don't include data points so no information on the accuracy of the contours can be inferred (it is like a scientist drawing a curve of best fit, then deleting the data points; you are deprived from seeing how well the curve fits the data!).

ABOVE: the correct map scale for Bikini Atoll, taken from Castle weapon test report WT-916. Let's now try to establish the correct fallout pattern for Castle-Koon. The error-filled DASA-1251 (the 1963 compilation of 'useful' fallout patterns, which misses out the reliable information in many cases and presents poor quality data in an even worse format), claimed of Castle-Koon:

'The fallout occurred ideally with respect to the measurement stations so that more readings than usual were available.'

This is echoed by the 1979 edition of Norment's U.S. Department of Defense DELFIC (Defense Land Fallout Interpretative Code) fallout prediction manual, volume 1, page 62 (see also page 61 for comparison of the inaccurate Koon fallout pattern with DELFIC prediction):

'... most of the Koon pattern area was covered by an array of fallout collection stations, so this pattern is probably reasonably accurate [unlike Zuni which is wrongly reported as being inaccurate!].'

In turn, this is echoed by a simplified version of DELFIC called AIRRAD which is used for the fallout predictions in the latest White House civil defence manual for dealing with terrorist nuclear threats. Page 1-22 of National Planning Scenarios states 'AIRRAD is used to predict fallout from nuclear devices.' AIRRAD (downloadable DOS version here) was evaluated in 1997 using the exaggerated Koon fallout map to 'validate' the predictions, with the report’s author echoing exactly what was written in the earlier DELFIC manual of 1979:

‘... most of the Koon pattern area was covered by an array of fallout collection stations, so this pattern is probably reasonably accurate.’ - Mathias J. Sagartz, Testing of the AIRRAD Fallout Prediction Code, Sandia National Laboratories, Albuquerque, New Mexico, report SAND97-2613, 1997, p. 19.
ABOVE: here is a better version of the Castle-Koon fallout pattern than that in the 1963 DASA-1251 compilation: it has the correct scale and it includes the data points from which the contours were constructed. It is taken from page 49 of the 1959 weapon test report WT-934. Notice that this version is quite different in detail, and that the upwind portion of the pattern is based on imaginative curve-drawing, not scientific evidence of the upwind extent of the fallout.

ABOVE: here is yet another version of the Castle-Koon fallout pattern. This one is from weapon test report WT-916, and we can ignore it since it is based on island readings only, and excludes data from the rafts anchored in the lagoon (the raft data is reliable, as the ratio of fallout gamma dose rate on a raft to nearby adjacent land was reliably measured to be 1/7, due to fallout sinking in the surrounding water). It is included to show how the fallout contour shapes are modified according to how much information you have available.
ABOVE: this is the source of the error-filled Castle-Koon fallout pattern used in the 1963 DASA-1251 fallout compilation, which comes from page 78 of 1956 weapon test report WT-915. Notice that the distance scale shown is totally wrong, and this error was inherited by the compilers of DASA-1251 in 1963, as I've pointed out before on this blog, particularly here (and in less detail here):

'WT-915 gives the distance from Enyu to Namu Islands to be 54 km, whereas it is actually 32 km, an exaggeration factor of 1.69 for the upwind fallout maps on Bikini Atoll for Castle shots Bravo, Koon, and Union. Since area depends on the square of distance, this means that the fallout areas are exaggerated by the factor 2.86. Morgenthau, et al. [DASA-1251, 1963], corrected the scale on the Bravo map of Bikini Atoll, but made the situation worse for the Koon and Union maps, where the distance from Enyu to Namu becomes 59 km and 56 km, and the distance exaggeration factors are 1.84 and 1.74, for Koon and Union, respectively. These imply fallout area exaggeration factors of 3.39 and 3.03, respectively.'

The great interest in Castle-Koon is that it is the only land surface burst ever conducted in the yield range of most modern nuclear warheads, 110 kt (of which 100 kt was fission).



Above: my fallout contour plot using all of the data for Castle-Koon fallout measurements from reports WT-915 and WT-916. There is a lot of uncertainty but the data are sufficient to at least provide some constraints on estimates of the size of the 250 R/hour at 1 hour gamma dose rate fallout hazard area from a 110 kt, 90% fission land surface burst!

It is worth summarizing some of the more reliable Nevada nuclear test empirical data for surface bursts JOHNIE BOY (0.5 kt, 1962), SUGAR (1.2 kt, 1951) and SMALL BOY (1.65 kt, 1962) which is tabulated on page 61 of Hillyer G. Norment's DELFIC report DNA 5159F-1, 1979 (his data for Pacific shots KOON and ZUNI are from error filled reports and are both obsolete). At 1 hour after burst, a measured gamma dose rate on point-source-calibrated survey meters of 100 R/hr at 1 m height over contaminated Nevada desert (corresponding to an ideal smooth plane dose rate of roughly 200 R/hr for a survey meter which isn't partially shielded by its own batteries and by the person holding it) occurred in an elliptical belt 0.25 km wide extending 2.73 km downwind from 0.5 kt JOHNIE BOY, 0.49 km wide extending 3.74 km downwind from 1.2 kt SUGAR, and 0.84 km wide extending 5.66 km downwind from 1.65 kt SMALL BOY. It should be noted that the exact depth of burst has a greater effect on the dangerous levels of fallout than the wind velocity. The wind doesn't affect the fallout dose rates very much, because if you double the wind speed, the same amount of fallout gets deposited over twice the area with therefore only half the concentration than for the lower wind speed, so the increase in downwind distance reached by any given fallout particle is largely offset by the fact that the particles are spread out over a greater tract of ground. Thus, in practice there is relatively little wind effect on fallout, apart from obviously determining the directions which the fallout plumes travel.

However, the fallout contour data show a great dependence on the exact depth or height of burst. Very shallow depths of burst greatly increase the cratering efficiency, producing more intense close-in fallout contours due to the extra activity carried by large particles contaminated at early times by the cratering ejecta mechanism. For example, the 1000 R/hr contour at 1 hour extended 1.38 km downwind and 0.26 km in width after the JOHNIE BOY 0.5 kt shot at 0.584 m depth, but such dose rates were confined to the crater in the 1.2 kt SUGAR burst detonated 1.067 m above ground!

Perhaps the best set of data comes from the 1962 SMALL BOY shot (1.65 kt Nevada burst at 3.05 m height above ground):

1000 R/hr at 1 hr reached 1.0 km downwind with a width of 0.28 km
500 R/hr at 1 hr reached 1.62 km downwind with a width of 0.41 km
200 R/hr at 1 hr reached 2.22 km downwind with a width of 0.54 km
100 R/hr at 1 hr reached 5.66 km downwind with a width of 0.84 km
50 R/hr at 1 hr reached 8.10 km downwind with a width of 1.42 km





Above: Dr Carl F. Miller's fallout model from 1963 is based on a semi-empirical analysis of the Pacific nuclear test fallout patterns from CASTLE and REDWING nuclear test operations in 1954 and 1956, in combination with a theoretical analysis of all the physics and chemistry of the fallout mechanism itself. (C. F. Miller, Fallout and Radiological Countermeasures, Stanford Research Institute, January 1963, vol 1 - AD410522, vol. 2 - AD410521.) Miller's model predicts an earliest fallout arrival time of 4W^0.2 minutes after burst, where W is the total weapon yield in kilotons. Hence, fallout under the mushroom cloud begins to arrive at 16 minutes after burst for 1 Mt, 22 minutes after burst for 5 Mt, and 30 minutes after burst for 25 Mt. (These data are from the DCPA Attack Environment Manual, Chapter 6, What the Planner Needs to Know About Fallout, U.S. Department of Defense, Defense Civil Preparedness Agency, report CPG 2-1AG, June 1973, Panel 29.)



Above: the earth penetrator warhead destroys hardened underground targets by ground shock and cratering with a low fission yield and can dramatically reduce fallout by trapping fission products deep within the crater ejecta layer. (The data for SEDAN is scaled back to 1 hour after burst using the decay rate curve, and thus exaggerates the radiation levels which occurred far downwind when the arrival time was greater than 1 hour.)



Above: Nevada nuclear test data shows the effect of burial on dose rate contours. Very shallow depths can enhance local fallout, but greater depths reduce it. Notice that the 100 R/hr contour at 1 hour after burst extends several km downwind for 1.2 kt surface or shallow detonations in dry soil, but much less than 1 km downwind for the bursts of 0.42-31 kt yields at depths of 34-110 m in hard rock.

Nevada surface bursts had yields from only 0.02-1.65 kilotons, while other Pacific surface bursts were in the multimegaton range, with massive fireballs that extended over the ocean or lagoon, sucking up sea water which affected the fallout. As Glasstone and Dolan explain on page 420 (paragraph 9.78) of The Effects of Nuclear Weapons, they were also conducted under conditions of extreme wind shear (directional change in the wind with altitude) which was done to confine the fallout more locally to the test area in a wide, shorter fallout pattern than would be the case in the absence of wind shear (where you get a long narrow fallout pattern that goes further and means having to patrol shipping over that longer tract of ocean).

The full Secret - Restricted Data set of eight reports in the 1251 series are:

1. F. K. Kawahara and H. Lee, Indexed Bibliography of the United States and British Documents on Characteristics of Local Fallout, U.S. Naval Radiological Defense Laboratory, report USNRDL-469 (DASA-1251 Volume 1), June 1961, Confidential.


2. M. Morgenthau, et al., Compilation of Fallout Patterns and related Test Data, U.S. Army Nuclear Defense Laboratory, report NDL-TR-34 (DASA-1251 Volume 2), 2 parts, August 1963, Secret - Restricted Data.


3. M. Morgenthau and R. L. Showers, Supplement - Foreign Nuclear Tests, U.S. Army Nuclear Defense laboratory, NDL-TR-34-Supplement (DASA-1251, Volume 2-Supplement), October 1964, Secret - Restricted Data.


4. R. L. Showers, et al., Part 3 - Nougat Through Niblick, U.S. Army Nuclear Defense Laboratory, report NDL-TR-34-Part 3 (DASA-1251, Vol. 2, Part 3), March 1966, Secret - Restricted Data.
   
5. F. K. Kawahara, et al., Annotated Compendium of Data on Physical and Chemical Properties of Fallout, U.S. Naval Radiological Defense Laboratory, report USNRDL-497 (DASA-1251, Vol. 3), November 1966, Secret - Restricted Data.


6. J. D. O'Connor and G. R. Crocker, Annotated Compendium of Data on Radiochemical and Radiation Characteristics of Fallout, Part 1: Specific Activity, Activity-Size Distribution and Decay, U.S. Naval Radiological Defense Laboratory, report NRDL-68-2 (DASA-1251, Vol. 4, Part 1), September 1968, Secret - Restricted Data.


7. L. R. Bunney, J. D. O'Connor and G. R. Crocker, Annotated Compendium of Data on Radiochemical and Radiation Characteristics of Fallout, Part 2: Radiochemical Composition, Induced Activity, and Gamma Spectra, U.S. Naval Ordnance Laboratory, report NOLTR 72-137 (DNA-1251F, Vol. 4, Part 2), May 1972, Secret - Restricted Data.


8. P. D. LaRiviere, et al., Transport and Distribution of Local (Early) Fallout From Nuclear Weapons Tests, Stanford Research Institute, SRI-4-3338/NDL-TR-65 (DASA-1251, Vol. 5), May 1965, Secret - Restricted Data.

Above: the table of fallout areas for measured dose rate contours in PLUMBBOB-SMOKY, 31 August 1957, Nevada, is taken from page 808 of the Hearings before the Special Subcommittee on Radiation of the Joint Committee on Atomic Energy, Congress of the United States, 86th Congress, The Biological and Environmental Effects of Nuclear War, June 22, 23, 24, 25, and 26, 1959, Part 1, U.S. Covernment Printing Office, Washington, 1959, 966 pages.




Now consider the unclassified sources of information on the nature of fallout (we have already discussed Dr Carl F. Miller's nuclear test fallout research here in an earlier post). The first detailed publication of the nature of fallout particles at two locations (near ground zero and far downwind) from two surface burst nuclear tests of approximately 5 megatons each (water surface burst Navajo and coral reef surface burst Tewa, both detonated at Bikini Atoll in 1956) is Dr Terry Triffet's published testimony to the U.S. Congress in 1959:

Hearings before the Special Subcommittee on Radiation of the Joint Committee on Atomic Energy, Congress of the United States, 86th Congress, The Biological and Environmental Effects of Nuclear War, June 22, 23, 24, 25, and 26, 1959, Part 1, U.S. Covernment Printing Office, Washington, 1959, 966 pages:

These hearings contain very important local fallout data, mainly in the testimony of the engineer Dr Terry Triffet of the U.S. Naval Radiological Defense Laboratory, California, but including useful contributions from many others, too.

Triffet's written testimony covers pages 61-100, mainly tables summarizing the fallout properties his team recorded at two stations (Station A - YFNB29 at 41,400 ft WSW of ground zero and Station B - LST611 at 313,000 ft NW of ground zero) for 5.01 Mt 87% fission coral reef surface burst Redwing-Tewa and also at two stations (Station A -YFNB13 at 39,800 ft W of ground zero and Station B - YAG39 at 111,000 ft N of ground zero) for 4.5 Mt 5% fission barge water surface burst Redwing-Navajo.

The first reference he gives in his testimony is to his report with LaRiviere, Characterization of Fallout, Project 2.63, Operation Redwing, Secret - Restricted Data. The 1961 version of that report has now been declassified and on pages 61, 77 and 79 the various graphs Triffet gave in his unclassified 1959 congressional testimony can be identified according to the nuclear test, while Dr Carl F. Miller's USNRDL-466 pages 20-21 give the distances of the stations from ground zero (as well as, on other pages, tables of neutron induced activity atoms-per-fission ratios and more detailed vital fractionation data for the samples from each of the fallout collection stations at those tests).

Comparing Triffet's 1959 congressional testimony to his 1961 secret report, you can see that he has done a very good job in summarising the best four sets of fallout data in the 1959 report to Congress, and he has converted the Navajo test data from its real fission yield of only 5% (very clean, 95% fusion yield) by multiplying up the reported fissions per square foot by a factor of 10.

Triffet's 1959 testimony to Congress doesn't directly quote specific activities for each location in units of fissions per gram, but he gives these indirectly these by revealing both the mass of fallout deposited per unit area (grams/sq. foot) and the activity deposited per unit area (fissions per sq. foot). By dividing the latter (fissions per sq. foot) into the former (grams/sq. foot), you of course obtain the specific activity, measured in fissions/gram. This is extremely important because it tells you how much bulk the fallout has, i.e. whether it is visible in dangerous deposits. Since you know the amount of fission in the bomb, you can use the specific activity of the fallout to calculate the total mass of fallout deposited from the mushroom cloud:

• 136 metric tons per total yield kiloton for the 3.53 Mt, 15% fission Zuni land surface burst (calculated using the best collected sample, the largest deposit of fallout mass which was from barge YFNB 29, pages 67 and 127 for 2.6 sq. foot sized collector trays in report WT-1317);


• 201 metric tons per total yield kiloton for the 5.01 Mt, 87% fission Tewa land surface burst (calculated using the best collected sample, the largest deposit of fallout mass which was from barge YFNB 29, pages 67 and 127 for 2.6 sq. foot sized collector trays in report WT-1317),


• 1,375 metric tons per total yield kiloton for the 365 kt, 73% fission Flathead ocean surface burst (calculated using the best collected sample, the largest deposit of fallout mass which was from barge YFNB 13, pages 67 and 127 for 2.6 sq. foot sized collector trays in report WT-1317);


• 655 metric tons per total yield kiloton for the 4.5 Mt, 5% fission Navajo ocean surface burst (calculated using the best collected sample, the largest deposit of fallout mass which was from barge YFNB 13, pages 67 and 127 for 2.6 sq. foot sized collector trays in report WT-1317).

(The higher fallout masses for the ocean surface bursts are due to the different energy partition in such bursts - energy is used to produce fallout in an ocean surface burst which in a land surface burst would be used for the cratering and ejecta phenomena - but even so these deposited wet fallout masses are not the total amounts of water involved. The masses refer to deposited fallout which on the close-in YFNB 13 location was a salt slurry consisting of droplets of salt crystals and salt-saturated water, altogether about 50% water and 50% salt by mass. Since ocean water is 3.5% salt by mass, clearly the mass of deposited fallout was only 1 part in 50/3.5 of the total ocean water involved in creating the fallout before evaporation occurred during the fallout process. I.e., the total mass of ocean water initially contaminated was 50/3.5 = 14.3 times greater than the values of deposited fallout measured for Flathead and Navajo. This evaporation occurred while the fallout was airborne not after deposition because the special collection devices for ocean fallout by Triffet and others prevented losses from evaporation after deposition. For an excellent study of how the slurry fallout evaporates and becomes droplets composed of a mixture of saturated salt and salt crystals, see N. H. Farlow, Atmospheric Reactions of Slurry Droplet Fallout in the Journal of the Atmospheric Sciences, Volume 17, Issue 4 (August 1960), pp. 390-9, and )

A useful check on these values of specific activity of fallout can be obtained from Dr Carl F. Miller's theoretical analysis in his ground-breaking 400 pages-long report Fallout and Radiological Countermeasures, Volume 1, Stanford Research Institute, January 1963, report AD410522 (this linked online PDF version is really poor quality and hard to read - it must be a scan of a microfilm print out which was made of a photocopy of a photocopy - but some of the important imformation is fortunately reprinted in chapter 2 another report by Dr Miller which is perfectly reproduced as a PDF file here). Miller begins Fallout and Radiological Countermeasures, Volume 1 with a simple discussion of the fallout creation process on page 3:

'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. ... radioactive elements can be subclassified into two groups by source. The first group contains the fission-product elements that are produced in the fission process ... The second group consists of the elements produced by the capture of neutrons released in both fission and fusion. The kinds and amounts of these neutron-induced radioactive elements in the fallout differ from one detonation to another depending upon the type of weapon used and the chemical elements in the environment at the point of detonation.'

On page 5, Dr Miller explains the radiation phenomena of fallout very simply and clearly:

'The potential hazard from the three types of nuclear radiations lies in the capacity of the different types of radiation to penetrate material, both living and inanimate, especially when the radioactive source is not in contact with the material irradiated. Thus, from fallout deposited on the ground, gamma rays are the only ones emitted that can penetrate large distances into the human body. The shorter-range beta particles can penetrate a short distance into material when their source is either in contact with its surface or is part of the material (i.e., an internal source). In general, alpha particles are not a fallout hazard because the alpha emitters are so extremely diluted and long-lived.

'The gamma rays, then, constitute an external hazard; the beta particles are often termed a contact and internal hazard; and the alpha rays constitute an internal hazard, of any. But since the major source of alpha particles in fallout is from the decay of unreacted uranium or plutonium, which are very long-lived radionuclides [i.e. the specific activity is very low because the emission of the radiation from each atom is spread over such an immensely long period of time compared to the very rapid decay rate of most of the fission products in fallout], the alpha particle hazard is negligible compared with that of the gamma and beta rays derived from other radioactive elements. ...

'The two radioactive emissions that are of concern in fallout, therefore, are the gamma radiations as an external source of hazard, and the beta particles as a contact or internal source of hazard. ... Both types of radiations cause injury to living organisms by producing ionization along their paths through living tissue. In other words, the rays or particles transfer energy to the electrons of the atoms in the material they penetrate. This causes the electrons to leave their orbits around the nucleus of the atom so that the atom takes on, for a short time, a positive charge.

'A specified amount of energy is required to ionize the atom: for every ion-pair formed by the passing of a gamma ray or beta particle near an atom, the ray or particle loses an equivalent amount of energy. The amount is not the same for all materials penetarted because the energy required to ionize an atom differs from one chemical element to another.'

Moving on to the physical chemistry of fallout creation, Dr Miller states on page 111:

'In summary, the over-all fallout particle formation process ... may be described as follows. In the first period of condensation, when the liquid and gas phases predominate in the fireball, the more refractory [unreactive] elements are dissolved into the liquid phase of the carrier material [i.e. molten glassy silicate sand from the Nevada desert] . The larger fallout particles, which fall away from the fireball while they are in the liquid state, will contain only these more refractory radionuclides. These particles will land nearest to the point of detonation.

'The smaller particles, that stay in the rising fireball for a longer period of time ... should carry radioelements that were condensed on their surfaces [because the fireball cooled below the melting point of the carrier prior to these particles being contaminated, so that the contamination lands on the outer solidified surface of the fallout particle and is then unable to diffuse into the particle, a process which can only occur if the soil particle is still molten when it is contaminated by fission products]. The smallest of the particles would make up the world-wide fallout or would be deposited at large distances from ground zero. (The world-wide fallout from air, sea water, tower, and surface bursts also contains vapor-condensed particles which have activity more or less uniformly distributed through their volumes.)

'The intermediate size particles, that deposit at intermediate distances from ground zero, should contain radioelements that were condensed during both [fission product and carrier soil] periods of condensation.'

To theoretically estimate the mass of fallout produced by this process, Dr Miller argues on page 133 that in a surface burst after the blast and heat flash have carried away some energy, half the remaining energy in the fireball 'is used to heat, dissociate, and expand the gas molecules from the air and half the energy is used to vaporize, dissociate and expand the gaseous products from the soil.'

For Nevada silicate soil with a melting point of 1400 C, Dr Miller calculates on page 151 that 7.5% of the total energy of a 1 kt Nevada surface burst is used to melt the sand into fused spheres of glassy fallout, and Dr Miller shows that this calculation is substantiated by test data:

'For a low yield tower shot [the Inca shot of Redwing, as identified by comparing the named test fallout particle photos in WT-1317 to the identical but unnamed test particle photos in USNRDL-TR-208], Adams [USNRDL-TR-208, 1957] estimated that about 3 percent of the energy was used in heating the soil and tower materials. Since it is expected that a larger fraction of the energy would be utilized in a surface burst, the two estimates are in relative agreement.'

Inca test, 1956: a 15.2 kt-bomb was fired on top of a 61-m steel tower (containing
165 tons of iron) over coral sand at Eniwetok Atoll. Magnetite particles
formed, and the mixed coral and steel formed marbles of contaminated black
dicalcium ferrite with veins of uncontaminated calcium hydroxide.
By measuring the ratio of calcium to iron in the fallout, the mass of coral
converted into fallout was found to be 264 tons. Only the top 2 mm of the sand
around ground zero was thus swept up by the afterwinds: ‘The fact that only a
thin layer of sand was actually either vaporized or melted, even though in
contact with the fireball... indicates that the thermal effects penetrate only
superficially into solid material during the short duration of the very high
temperatures. By computing the energy required to heat, decarbonate, and melt
264 tons of coral sand and to heat, melt and vaporize 165 tons of iron ... 8.5%
of the available radiant energy [i.e., 3% of bomb yield, because the radiant
energy was 35% of the total energy of the explosion] was utilised for heating
the tower and soil material.’ - Charles E. Adams and J. D. O’Connor, U.S. Naval
Radiological Defense Laboratory, report USNRDL-TR-208, 1957, p. 13.

Dr Miller then calculates on page 154 that this 7.5% of the 1 kt surface burst bomb energy will melt 192 metric tons of Nevada silicate soil into fallout, i.e. about 3.8% of the cratered mass. Clearly, therefore, about 192 metric tons of fallout per kiloton of total yield can be expected for a Nevada type silicate soil surface burst. This figure also agrees closely with the range of 136-201 metric tons per kiloton of total yield derived above from the Redwing coral soil surface burst fallout specific activities for Zuni and Tewa. For ocean water surface bursts, Dr Miller explains on pages 329-30:

'Because the end of the first period of condensation for a water shot occurs at about 0 C, very little fractionation of the fission products (with possible exception of the rare gas elements) should occur, especially for the larger yield detonations. This longer period of condensation for the water before the final sea water fallout particles are formed by vapor condensation should result in more thorough mixing of the water and the fission products, as well as in rather uniform concentrations of the radioactive elements in all fallout particles or drops. ... In warm (dry) climates and over land areas ... the fallout pattern would extend much further downwind than would be estimated from use of the simple scaling system for land surface detonations. This is simply because the droplets, decreasing in size and density as the water evaporates, would be carried to greater distances and dispersed over a larger area. Under these conditions, the deposit levels would all be decreased.'

Returning to the 1959 Congressional Hearings, Triffet picks out the most reliable data from the massive test report in his congressional testimony, although two of the graphs he gives in the written testimony are virtually fictional: the 'Near Station' and 'Distant Station' graphs he gives on page 76 of the 1959 hearings are linked to close-in and distant locations in the Tewa fallout pattern, but are actually Zuni trivial fallout collection graphs for collection stations on YFNB13 (with the dose rates multiplied up by a factor of 1,000 to make them look more impressive) and YAG39 (with the dose rates multiplied by by a factor of 10). We'll ignore those two graphs, and just concentrate on the accurate tables of information Triffet provides which are based directly on the Characterization of Fallout report.

First, some general comments about the 1959 congressional hearings. I have published on this blog the most useful extracts from the 1957 Congressional Hearings by the same Subcommittee of the Joint Committee on Atomic Energy. The most useful reports on fallout in the 1957 hearings came from the U.S. Naval Radiological Defense Laboratory, including reprints in full of Edward A. Schuert's USNRDL-TR-139 paper, A Fallout Forecasting Technique with Results Obtained at the Eniwetok Proving Ground. The 1959 hearings were presided over by Representative Chet Holifield, who says in his opening statement on page 3:

'We are particularly indebted to Dr Paul Tompkins and his associates of the U.S. Naval Radiological Defense Laboratory.'

Officially, the 22-26 June 1959 on the Biological and Environmental Effects of Nuclear War hearings were supposed to be centred around studying the consequences of a hypothetical nuclear war utilizing the actual global wind patterns for 17 October 1958, in which 1,446 megatons consisting of 263 weapons of 1-10 megatons (mean yield 5.5 megatons) with 50% fission yield, were ground surface burst on 224 North American targets (111 Air Force installations, 71 population and industrial target areas such as cities, 21 Atomic Energy Commission nuclear installations, 12 Army installations, 5 Navy installations and 4 Marine Corps installations) by Russian bombers, ICBMs and submarine-delivered missiles, and 2,500 megatons were dropped on Russia by North America in retaliation. But in fact, this attack study only takes up a few pages of the Hearings near the beginning and a few pages near the end: the majority of the volume is a study of all the details of the effects of nuclear weapons tests without any reference whatsoever to any particular nuclear attack scenario.

(The results of the hypothetical attack mentioned were calculated by electronic computer with the results published on pages 855-858. It was found that out of 150 million Americans - of whom 42 million lived in the 12 largest cities - 19.7 million people would be killed on the first day, with a further 22.2 million fatally injured. The worst single casualty rate was in New York City with 3,364,000 killed in the first 24 hours and an additional 2,634,000 fatally injured. Initial effects were based on scaled-up Hiroshima-Nagasaki nuclear casualty data, with fallout doses extrapolated from Pacific nuclear weapons testing data. On page 858 it is stated that the mean gamma radiation dose to all North American survivors for the first 3 months after the attack was computed to be 110 R, but the non-injured survivors received a mean dose of only 60 R. Those survivors, Herman Kahn declared, would certainly not envy the casualties. Assuming no ‘duck and cover’ and no civil defence against fallout, 13% of the population would be killed on the day of the attack, while 15% would die later from burns and radiation. Thus a total of 28% or 49 million would be killed. Of 46 million American houses, 26% would be demolished, and 21% damaged. The land area covered by fallout gamma dose rates exceeding 0.1 R/hr would fall from 46% at 2 days to 15% at 2 weeks and to only 5.8% at 12 weeks.)

The first nuclear testing expert witness to testify on the effects of nuclear weapons at those 1959 hearings was the physicist Dr Frank Shelton, the Technical Director of the Defense Atomic Support Agency, Department of Defense. On page 15, Shelton states:

'An accumulation of about 700 rem [=700 cSv] in 48 hours for an unshielded person can be expected to occur over about 1,500 square miles from a 10 megaton surface burst (50 % fission); that is, an area that could be about 100 miles long and about 17 miles at the maximum width. Few people appreciate the fact that, for the same bomb, second degree burns on the exposed face and hands and the ignition of fine kindling fueld can encompass an area of about 25 miles radius or about 2,000 square miles in the immediate vicinity and perhaps dense population of the target area. That is, this thermally affected area could be substantially larger than that of the lethal fallout area. And, if there is some shielding of personnel in the downwind fallout areas, the thermal effects area would certainlly be the larger of the two.'

This is all complete nonsense, based on the flawed thermal radiation transmission theory used in the 1957 edition of The Effects of Nuclear Weapons and its flawed thermal effects data, which was not corected until the February 1964 (not the April 1962) edition, after new studies had been independently done by two different laboratories.

Dr Carl F. Miller, who worked for the U.S. Naval Radiological Defense Laboratory at later nuclear tests to measure fallout on ships with washdown safeguards that were sailing under the expanding mushroom clouds, pointed out in the February 1966 Scientist and Citizen:

‘Reliance on the Effects of Nuclear Weapons has its shortcomings ... I was twenty miles from a detonation ... near ten megatons. The thermal flash did not produce the second-degree burn on the back of my neck, nor indeed any discomfort at all.’

Miller explained the facts clearly on page 353 of volume 2 of his January 1963 Stanford Research Institute report Fallout and Radiological Countermeasures (AD410521):

'If a potential response level of humans (or other objects) to the intensity of the four phenomena is selected, such as the intensity that could result in a large fraction of fatalities, then statements can be made about the relative order in the size of the affected areas enclosed by each of the phenomena for the selected response level. For example, the relative sizes of the areas enclosed by the four phenomena from the detonation of a standard nuclear weapon in the megaton range near the surface of the earth, where the perimeter of the affected areas is defined by a (potential) response level equivalent to about 50 percent human fatalities, are, largest to smallest: (1) fallout, (2) thermal radiation, (3) blast, and (4) initial nuclear radiations.

'In this example, the area covered by radiation levels high enough to produce [in the absence of any countermeasures, e.g. for people remaining exposed to fallout in open outdoor areas with no kind of radiation shielding or decontamination whatsoever] the stated minimum level of potential response would be nearly 100 times larger than the area affected by thermal radiation and giving the same effective response (i.e., about 50 percent deaths).'

Shelton after blundering on the thermal effects by following Glasstone, then more usefully states on pages 40-41:

'Blast overpressure is itself not a very significant casualty agent. ... However, secondary effects and injuries caused by crumbling buildings, flying debris and translation of man himself are certainly very significant. Extensive blast injury can be expected at distances at which brick apartment houses collapse ... I would expect extensive window damage at 25 miles from a 1-megaton burst, and it would be an extreme hazard out to about 7 miles. Don't stand behind windows in an attack. First you will get burned and then you will have fine glass splinters driven into you very deeply within distances like 7 miles from a 1-megaton burst. ... Glass in any disaster like the Texas City disaster is one of the primary materials found in the normal home which can result in blinding and all other types of effects due to the flying small splinters of glass.'

Notice the vital fact here: serious glass injuries occur out to 7 miles from a 1 megaton surface burst but windows are broken out to 25 miles!

All of the popular anti-civil defence trash published about the effects of nuclear weapons does not recognise this distinction and claims that glass is a hazard out to the radius where windows are just broken. Not true. Windows were broken in Las Vegas after numerous 1950s Nevada nuclear tests, but that is not the same thing as the glass hazard range, which comes from the blast winds behind the shock front accelerating the glass fragments and hurling them radially outward from the explosion at high velocity. This requires higher overpressures than are required to merely break a glass window. It's easy for a weak shock front to break a glass window, especially a large one. (Simply multiply the area of the window by the peak reflected pressure to find the peak force the window pane is subjected to.) That weak shock wave will not, however, have a significant dynamic pressure associated with it, so there will not be any significant blast wind to accelerate the glass fragments, which will simply fall down vertically outside the window. To make glass a missile hazard, you need substantial dynamic pressures so that the wind following the shock front (which breaks the glass) can accelerate the glass fragments to a large horizontal velocity.

This is what constitutes the glass missile danger to people standing behind windows 7 miles from a megaton explosion but not at 25 miles (where windows are broken, but the glass falls vertically to the floor instead of being fired horizontally into the face of anyone who has ignored the delayed blast arrival risks and not bothered to 'duck and cover'). Page 331 of those Hearings shows that for ~20 kt Nevada tests there is a big hazard for 1.9 pounds/sq. inch peak overpressure blast, where glass window fragments have a mean mass of 1.45 grams and a mean velocity of 108 feet/second, but the stronger blast wave of 5.0 pounds/sq. inch breaks the window into smaller fragments of just 0.13 grams mean mass, so although those fragments have a high mean velocity of 170 feet/second, their momentum is decreased relative to those produced by 1.9 pounds/sq. inch. hence there is an optimum peak overpressure for the production of grass fragments that pose a maximal hazard. At low overpressures, the fragments are large but have small velocities so they are relatively harmless. At very high overpressures, glass fragments were observed to have optimal speeds - even approaching the blast wind velocity itself after long times in the blast wave - yet they are so tiny that they have little momentum and thus little penetrating power to cut their way through normal clothing or through the abdominal wall of the body. A very strong shock wave shatters glass panes into a very fine powder of glass fragments with relatively little individual momenta. The worst effects come from intermediate overpressures, where the wind pressure is sufficient to accelerate the fragments to large speeds, but where the shock front is not strong enough to shatter the glass into too many small fragments (ADA397401; ADA383465; ADA394861; ADA395151). In any case, ducking and covering the face offers substantial protection from the effects of glass observed at Hiroshima.

This is off-topic for the blog post here, but it is important to quote it for civil defence purposes: duck-and-cover civil defence advice is based on nuclear test evidence. Ducking and covering stops you getting thermal flash burns and blinded by flying glass. That's not silly or stupid advice, judging by the numbers of people who were burned and injured by flying glass in Hiroshima and Nagasaki. Preventing such injuries actually increases the chance of survival from nuclear radiation, by preventing infectioned wounds from existing when the white blood cell count (which fights infection) and platelet count (which clots blood to prevent excessive bleeding) is low after nuclear radiation exposure (the synergistic LD50 for nuclear radiation is lowest in the case of simultaneous burns and other trauma, which is why so many people were killed at low radiation doses in Hiroshima and Nagasaki - see paragraph 12.112 of The Effects of Nuclear Weapons).

Above: Triffet's 1959 Congressional testimony focussed on fallout from land and ocean water surface bursts, summarizing the data from his and Philip D. LaRiviere's Characterization of Fallout report for two locations from each of the approximately 5 megaton Redwing shots Tewa (land surface burst) and Navajo (ocean water surface burst).

Above: Triffet's 1961 WT-1317 fallout pattern for the 4.5 Mt, 5% fission (very clean) Navajo surface water shot at Bikini Atoll in 1956. This fallout pattern, like those Triffet gives in WT-1317 for Zuni, Flathead and Tewa, combines all data and reconciles the lagoon and atoll radiation measurements with the ocean survey data, unlike the DASA-1251 compendium which gives disjointed data without closed contours and is based on an inaccurate report (WT-1344).

Above: Triffet's comparison of the cabbage-shaped fallout pattern from the 5.01 megaton land surface Tewa shot at Bikini Atoll in 1956 (left) to the banana-shaped fallout pattern from the 1.2 kiloton land surface Sugar shot in the Nevada in 1951. This created a lot of interesting discussion in the 1959 U.S. Congressional Hearings on the Biological and Environmental Effects of Nuclear War testimony, because Dr Triffet argued that the complexity of the 5 megaton burst fallout pattern was due to its large yield: having a large yield meant a very high mushroom cloud, which was more likely to be subjected to directional 'wind shear' in the wind layers all the way up to 100,000 feet than the case of the lower cloud from a 1.2 kiloton surface burst which only rises to say 10,000 feet. (The downwind hotspots in Pacific test fallout patterns had already been publicised by Dr Paul C. Tompkins, scientific director of the U.S. Naval Radiological Defense Laboratory, in his testimony before the Holifield Civil Defence Hearings, House Government Operations Committee, May 2, 1958, pages 209-210: 'the major residual radiation threat does not occur within range of physical damage.' Dr Tompkins added that the peak fallout dose rate in large Pacific surface bursts occurs not at the crater but typically in a hotspot 50-75 miles downwind.)

On pages 109-110 of the 1959 U.S. Congressional Hearings on the Biological and Environmental Effects of Nuclear War, Triffet explains to Representative Holifield:

'The contours from the large burst are very irregular compared with those from the small burst. This is because the megaton burst produces a cloud which rises into the high level winds, and these may vary in direction. ... Notice the contours of the 1 kiloton burst. The cloud did not get into the high-level winds in this case; consequently, it is easy to see how the contours could be generalized into a cigar shape. ... There is another factor that should be brought out, too, and that is that the winds over the Eniwetok Proving Grounds [which included Bikini and Eniwetok Atolls] have a tendency to vary more than the winds over the United States - the high-level winds, that is.'

The next day (page 208 in the printed Hearings), meteorologist Charles Shafer pointed out to Representative Holifield:

'With regard to irregularities of fallout deposition, Dr Triffet showed yesterday an analysis of a multimegaton detonation in the Pacific in which there was a tremendous fanning out of the fallout with several hot spots. I would like to make it clear to the committee that ... we do not have that type of wind behavior in the United States except possibly in the Gulf States in the summertime, only one season out of four.'

Above: Triffet's 1959 Congressional testimony gamma dose rate decay curves for Tewa stations A (barge YFNB 29) and B (ship LST 611). Curve B is essentially valid for unfractionated fallout and also serves therefore to describe the decay rate of all fallout from sea water surface bursts, where the water's low boiling point (only 100 C) in comparison to the boiling point of soil means that it takes so long for fallout droplets to condense in a water surface burst that there is no fission product fractionation possible.

Above: Triffet's 1959 U.S. Congressional testimony curves showing land surface burst mass deposit in a sequence of small circular trays 8 cm in diameter, together with the gamma dose rate from the fallout deposited over a much larger area of the barge or ship. The masses deposited in the sequentially exposed collection trays are more irregular and erratic (because of the small size of the trays) than the gamma dose rate which comes from a massive area of tens of metres around the detector, and so averages out the effect of a lot more fallout mass being deposited, but despite this sampling difference, the curves do show the relationship between the transitory period of fallout deposition, and the way that the dose rate from the radiation builds up, peaks where the rate of arrival of fallout compensates for decay, and then falls.

Above: Triffet's 1959 U.S. Congressional testimony curves showing sea water surface burst mass deposit in a sequence of small circular trays 8 cm in diameter, together with the gamma dose rate from the fallout deposited over a much larger area of the barge or ship. Notice especially that the gamma dose rate curve varies fairly abruptly with the rate of fallout deposition, which is due to a large fraction of the dose rate during deposition being due to 'skyshine' from airborne wind carried particles. Once the cloud is blown past the detector, the dose rate falls rapidly (faster than the decay rate) because that source of radiation is physically removed by the wind.

Above: the incremental fallout collector of the type used for nuclear test operations Castle, Redwing and Plumbbob. A stack of hundreds of circular fallout collection plates, 8 cm in diameter, were exposed to fallout incrementally for periods of a few minutes then replaced, with the exposed tray being carried down automatically by an elevator system powered by compressed air. This instrument, manufactured by the U.S. Naval Radiological Defense Laboratory in large numbers for automatic fallout sampling on the ground at many locations in the fallout area, was more innovative than any of the radiation monitoring instruments. The first version was used at Mike shot in 1952 and was simply a box with an array of trays in fixed positions and a moving belt (motorized with a clock) with slots cut in it above the trays, so that each tray would be exposed to fallout for a 2 or 5 minutes interval, depending on the distance from ground zero. This was replaced by the elevator system (above) which allowed larger trays to be exposed and to collect larger samples of fallout. The beauty of this system is that the time of arrival of fallout, and the duration of fallout deposition, can be ascertained to enable the deposition-contamination hazard duration to be assessed (you can't do this by measuring the radiation level, because the radiation continues after the fallout mass has stopped arriving). The whole effort began in 1951 when simple open fallout collection trays were exposed in an effort to collect the Nevada Sugar and Uncle fallout, but of course became filled with blast wave wind carried non-radioactive dust, so it was not clear what proportion of the immense mass of the deposition in the open trays was fallout and what was blast raised dust from the desert. So incremental collectors were invented to expose trays in turn for a certain number of minutes before covering the tray and keeping the contents safe for later analysis in the laboratory.

... This post (like the previous one) is as yet incomplete and is to be continued as time permits (dealing with local fallout patterns, cloud activity by rocket instrument survey, and deposited fallout mass and radiation characterization for Ivy, Castle and Redwing surface bursts, plus the Nevada surface bursts and shallow underground cratering tests).