Digital Archive digitalarchive.wilsoncenter.org International History Declassified February 28, 1955 Report by the Measurement Lab of the USSR Academy of Science, 'On the Properties of the Atomic Bombs Detonated on the Marshal Islands in 1954' Citation: “Report by the Measurement Lab of the USSR Academy of Science, 'On the Properties of the Atomic Bombs Detonated on the Marshal Islands in 1954',” February 28, 1955, History and Public Policy Program Digital Archive, Archive of the All-Russian Scientific Research Institute for Experimental Physics (VNIIEF), f. 1, op. 20snt, ed. khr. 602, l. 1-27. Document no. 138 in Atomnyi proekt SSSR. Dokumenty i materialy. [The atomic project of the USSR. Documents and materials.], vol. 3, book 2, p. 318. Translated for CWIHP by Ronen Plechnin. https://digitalarchive.wilsoncenter.org/document/118803 Summary: Soviet scientific intelligence report on U.S. nuclear weapons testing on the Marshall Islands in 1954. This report concludes that the Ivy Mike and Castle nuclear detonations were thermonuclear based on gamma ray spectroscopy of fission fragments collected by Soviet aircraft over the USSR and PRC. Credits: This document was made possible with support from Carnegie Corporation of New York (CCNY). Original Language: Russian Contents: English Translation Order of Lenin The Laboratory of Measurement Tools, AS USSR [Lab No. 2] Affirmed by, Director of the Laboratory of Measurement Tools AS USSR Member of the Academy—I.V. Kurchatov 28 February 1955 “On the Properties of the Atomic Bombs Detonated on the Marshall Islands in 1954” Director of Sector No. 3 – I.V. Kurchatov. Senior Scientific Associate- S.A. Baranov Junior Scientific Associates – A.G. Zelenkov, R.I. Polevoi, L.V. Chistiakov City of Moscow—1955 No. 58 A Report by the Measurement Lab of the USSR Academy of Science “On the Properties of the Atomic Bombs Detonated on the Marshall Islands in 1954” Affirmed by, 28 April 1955 Director of Measurement Laboratory AS USSR, Top Secret Member of the Academy- I. V. Kurchatov (Special File) Abstract In this report we present the results of the first systematic study of the American atomic bombs [tested in the Marshall Islands]. The study is based on a radiochemical analysis of samples of fission fragments collected from the atmosphere. A detailed presentation of the experimental material is given in a separate report. Table of Contents: 1. The Goal of the Study 2. Evaluation of expected radioactivity 3. On the sampling of radioactive materials 4. Radiochemical analysis results 5. Atmospheric Contamination by radioactive products. 6. Conclusions 7. Literature 1. The Goal of the Study During the period March–June 1954, a comprehensive study of radioactive dust that was collected from the atmosphere took place in the USSR for the first time. The study was complemented by a radiochemical analysis of the materials that were collected. This study was conducted with the goal of obtaining information about the properties of the atomic bombs tested by the United States on the Marshall Islands in 1954, as well as with the additional goal of evaluating the level of atmospheric contamination at the moment of the radioactive cloud’s passing over the territory of the USSR. A full isotopic and radiochemical analysis of the fission fragments enable us to obtain answers to the following questions: 1. What type of bomb was tested, and was that bomb thermonuclear? 2. What is the proportion of the thermonuclear yield compared to the fission yield? 3. What heavy fissile isotopes were used in the bomb? 4. What light elements were used? A large quantity of radioactive material was collected for the purposes of this study. 2. Evaluation of Expected Activities The work of collecting radioactive dust was based on preliminary reports, which in turn were based on Davidenko’s evaluations (1), and on the first experimental results, obtained by Ushatski, Kirin and others (2), that address the issue of the capturing and the analysis of fission fragments released to the atmosphere in the aftermath of the American atomic test in the Marshall Islands on 1 November 1952 [Ivy Mike]. Based on the yield of the bomb at 17 million tons of TNT, as well as the assumption that most of the energy release resulted from the fission of heavy atoms, V.A Davidenko calculated the average concentration of expected radioactivity in the atmosphere at 10- 9 Ci/L. This figure does not take into account the erosion of the radioactive material from the cloud, and that the volume of the clouds was specified rather arbitrarily at 0.001 of earth atmosphere. Therefore the cited figure 10-9 Ci/L may be slightly exaggerated. The second of the said studies enables us to obtain the concentration of activities from the experimental data. In this case, radioactivity was measured to be about 0.5 micro-curies, corresponding to a concentration 5x10-16 Ci/m3 at the time of sampling. This last figure should be corrected and increased, given that from the moment of the bomb’s detonation 1 November 1952 to the moment of the capturing of the aerosols over the USSR (March 1953), a period of three and a half months had passed. That led to a decline in volume and to the scattering of the clouds throughout the entire atmosphere. Introducing corrections to scattering and volume calculations may increase the concentration to 5×10 -12 ten days after the explosion. This last figure was used at the time of the program’s initiation. In order to produce a thorough isotopic analysis of the fissile materials, it is necessary to collect radioactive materials at levels of about 50 µCi. For a radiochemical analysis, which would enable us to identify the type of the e, a smaller number of [unclear] micro curie would suffice. 3. On the Sampling of Radioactive Materials At the expected concentration 5×10 -12 curie\liter, activity at 10 µCi could have been collected with special filters that were installed on airplanes which travelled hundreds of kilometers inside a radioactive cloud. At the time of the detonation of the atomic bomb, the radioactive cloud, which is composed of radioactive particulate, is ejected into the upper atmosphere. At altitudes higher than 5000 meters, the cloud may be caught up in a permanent wind zone, moving predominantly from the west to the east at speeds of 50–150 km/h. Under these circumstances, the radioactive cloud might, as it moves from west to east, circle the earth and appear first over the west of Europe, and then over the territory of the USSR as well. That is why flights over the USSR were conducted in the meridian direction (across the assumed direction of the radioactive cloud) from 60°N to 46°N. The airplanes were flying mostly over the route Poltava—Leningrad—Odessa—Poltava, at an altitude of between three to eight thousand meters. In order to collect the particles from the atmosphere, the airplanes were equipped with cone shaped Petryanov filters [P.F] which can capture 100% of the aerosols. The filters, placed in the in the nacelles of the TSAGI, which were strengthened underneath the plane. The evaluation of the activity which accumulated on the filters was made after each flight with the help of portable type PR-6 radiometers. The radiometers were pre-calibrated under controlled laboratory conditions. When radioactive materials accumulated, the filters were dismantled and sent to the Laboratory of Measurement Tools at AS USSR for radiochemical analysis. The first flights over the territory of the USSR did not detect increased radioactivity levels in the air up to 20 March 1954, although already on 10 March 1954 one could anticipate the appearance of a radioactive cloud over the territory of the USSR, resulting from the blast on 28 February 1954 [Castle Bravo].Apparently the cloud passed over the southern part of the USSR. Since the Marshall Islands are located at 10°N, it was essential to examine the radioactive air as close as to the equator as possible. With this goal in mind, flights were organized on the route Beijing—Canton— Beijing. This enabled us to control the “belt,” running from 40°N to 23°N. Flights to the USSR continued as well, that is, control [samples] were taken from a significant part of the atmosphere of the earth’s northern hemisphere. The outcomes of our work demonstrate that sending the expedition to the PRC was a very appropriate decision. Conditions suitable for the identification of clouds and for the gathering of radioactive samples were much more favorable in the PRC than in the USSR, allowing for the collection of a much larger amount of radioactive material. The radioactive materials collected by the expedition enabled us to identify two explosions which would have been impossible to study if the materials were gathered over the territory of the USSR. During the expedition’s work, it was also discovered that layers of used oil covering the engine’s nacelle contained significant radioactive activity, comparable to the radioactivity on the Petryanov filters. That is why the fuselage and wings of the airplane, which was on its way to its next trip, was covered by special glue which could be washed off and studied for radioactivity after each trip. The varying levels of radioactivity in particles that were washed off after each trip enabled us to monitor the changes in the concentration of radioactive aerosols in the atmosphere over the Beijing—Canton routes, although we had to take into account the long duration of the flights. The measurement of the rate of decay of the samples, obtained during the wash-out process, enabled [the team] to [identify the date of the explosion] and thereby to calculate the time it took the cloud to reach PRC.