Letter to Scientific Director, Joint Task Force, Subject: Nuclear Radiation Measurements for Atomic Bomb Tests (Sandstone Operation)

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BEST AVAILABLE COPY war and Navy de IN REPLY REFER TO: SUBJECT* Nuclear Radiation Measurements for Atomic Bomb Tests* TO: Scientific Director* Joint Task Force 1* A letter dated 9 September 1947 from Doctor Herbert Scoville, Jr. to Captain James S* Russell, USlf, AEC, set forth a preliminary outline of the nuclear radiation measurements which the Radiological Division of the Armed Forces Special TJeapons Project considered desirable in the forthcoming tests* Since that date, this program has been discussed with representatives from Los Alamos and various other cognizant activities* As a result of these discussions, certain modifications ’of this program have been made and steps have been taken to inclement certain of these projects. The revised and amplifiedeprogram is included as 2* It should be emphasized that this is a coordinated program designed to obtain information on all the important nuclear radiation effects of an atomic bomb detonation. Undoubtedly, the individual military services will also propose many projects similar to those listed in this inclosure. However, because of the joint nature of the Armed Forces Special Weapons Project, this program has been designed to obtain the information which will be required by all services. Coordination of all nuclear radiation measurements is felt very desirable in order that the results of the separate projects can be properly interpreted and correlated. In the event that ary further service projects of a similar nature receive approval of the Scientific Director and the Task Force Commander, the Radiological Safety Section will endeavor to integrate these with its program for the overall simplification of the operation* 3* Specific concurrence in the inclosed program is re quested so that steps can be taken to implement it immediately. The Radiological Safety Section is prepared, with the approval of the Scientific Director, to assume specific responsibility for carrying out those projects which are not being directly undertaken by the Los Alamos group. In some cases arrangements will be made with other military services to assist with the individual projects. Nuclear Radiation Projects

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BEST AVAILABLE COPY IN REPLY REFER TO: WAR AND NAVY DEPARTMENTS ARMED FORCES SPECIAL WEAPONS PROJECT Inclosure 1 - HUCLEAR RADIATION PROJECTS 1# Gamma Radiation Measurements aa Gamma Dosage versus Distance - This will be measured by means of films placed at various distances from the point of detonation. Approximately 500 films will be required for this purpose and these will be attached to stakes stationed at 100 yard intervals from the point of detonation. Several films will be placed at each station. Attempts will be made to protect the films from the heat flash. Additional films may also be placed at various other locations which will be carried out by the regular personnel of the Radiological Safety Section. Development and analysis of the films will be arranged by the Armed Forces Special Weapons Project. b. Gamma ray spectrum - The Los Alamos group has already made arrangements with Doctor Shonka to carry out tests to determine the gamma ray spectrum. The logistic support required for this project and the personnel required will be included in their program. These measurements are vital to an understanding of the nature and effectiveness of the gamma radiation and form an integral part of the nuclear c. Gamma intensity versus tine - Doctor Lauriston Taylor of the National Bureau of Standards has been approached by the Armed Forces Special Weapons Project to see if he could carry out this project which is extremely important for the point of view of determining the source of the extremely penetrating gamma rays. A preliminary study of the problem has been made by Doctor Taylor and his suggestions for the required instruments are included as Appendix I to this memorandum* In accordance with this estimate, the logistic support for this program would amount to about thirty-five tons, most of which will be needed for the shielding of the instruments. It is possible that later analysis will permit the reduction of this shielding to some extent. As soon as approval of this project is received, steps will be taken to implement this BEST AVAILABLE COPY

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BEST AVAILABLE COPY Page 2 of Inclosure 1 l d. Location emd diffuseness of source - This measurement is of considerable value in estimating the effectiveness of shielding against gamma radiation and will also be of considerable value in supplementing the experiments listed in the preceding paragraphs. Orientometers could be constructed to study this effect along the lines used to measure the location of the visible light produced in Test Able. The thickness of the protecting shields would of course, have to be greater because of the greater penetration of the gamma rays. This rather simple measurement, however, will be a valuable supplement to the data obtained by . the more complicated and less sure methods used in projects l(b; and (c). The logistic requirements for this project will be about one ton, and if approved, steps will be immediately taken to get the devices con structed. The orientometers used at Bikini were con structed by the Naval Ordnance Laboratory. The Armed Forces Special TJeapons Project will make the ne'cessary arrangements to have the devices constructed for these tests by this or some other group. Absorption by thick and angular shields - It is proposed to set up shields of known but varied thicknesses of steel and concrete at about l/2 mile from the point of de tonation. These will be placed not only at right angles t to the source, but also at various oblique angles. Analysis of the results at Bikini indicate that this information is vital in estimating the efficiency of any shield. It will be required both for the design of new naval vessels and for the design o£ shelters against atomic bomb attacks. These measurements are extremely simple to make, the only requirement being the location of the shields at given distances from the point of detonation. To attempt to set up laboratory experiments to give the same information would be an extremely complicated and difficult task because of the size and complexity of the source. The results thus obtained , would always require interpretation and might be open to considerable question. Furthermore, the laboratory experiments would require completely satisfactory re- - suits from projects 1(b) and (d) in order to be of any value. This shielding experiment will provide a practical answer with a minimum of effort. The results . obtained would be extremely valuable to all branches of the military services. The logi^t^ support for

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Page 3 of Inclosure 1 this will he approximately ten tons, assuming that separate shields will he required for each test. Half of this weight will he concrete so that if it is poured at the site, a reduction of the transportation require ments will occur. However, there are certain advantages to preparing standard shields here and transporting them to the site. f. Determination of the gamma radiation due to residual con tamination - This measurement is required as a standard for all the other measurements on gamma radiation, since they will he impossible to interpret without being able to differentiate between the prompt and residual gamma radiation. The logistic support for this will he approximately one-half ton of lead shielding. It is planned to use lead containers which will be designed so that the blast pressure will drop a film badge into a. Ufeutron Spectrum - The Los Alamos group is planning to measure the neutron spectrum at energies greater than 3 I3ev. From a biological point of view it is important to have the energy range estimated down to at least 0.1 Hev. Certain elements are known which can probably be .used to acconplish this purpose. These were discussed with Doctor Graves, and it is recommended that if they are practical, they be added to the elements already being used. The logistic support for the expansion of these measurements will be negligible. b. Neutron flux versus distance - This is also already a part of the plan of the Los Alamos group since the elements used in 2(a) will be placed at various distances from the point of detonation. c. Neutron absorption and scattering - This can be accomplished by placing the elements used by the Los Alamos group behind the shields used for project 1(a). As a con sequence, no additional logistic support is needed for this project, but it provides further justification for the use of the shielding materials in project 1(6). BEST AVAILABLE COPY

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BEST AVAILABLE COPY Page 4 of Inclosure 1 Carrying out this experiment in the laboratory is like wise difficult because of the conplexity of the source . and the necessity of obtaining conplete results from a. Direct contamination of the ground in the irmediate vicinity of the point of detonation - It is planned to run decay curves and some radio-chemical analysis of samples and materials collected from the crater. A small part of the samples being collected by the Los Alamos group will be needed for this project. The decay curvaa-3gill_ha— started at the site by the Radiological- Safety Technical Service'17nit,—'Bince_the results will be of immediate value in the safety program. The chemical analyses, however, will be made at a laboratory in this country. Arrangements for this will be made by the Armed Forces Special Weapons Project. These studies are very im portant for an tinderstanding of the nature and serious ness of the ground contamination. b. Downwind fallout - These studies will of necessity be limited since it appears likely that most of the fallout will occur in the water rather than on land. Any samples of active water, however, will be collected and analyzed, and likewise, the land areas downwind will be investigated to see if any fallout has occured. These measurements are directly tied in to the safety program and will be useful in estimating the extent of this hazard in further operations. Any analyses which are possible will be done in the same manner as for 3(a). No special logistic support will be needed for this program, since the samples will be collected by the Radiological Safety personnel monitoring the .downwind areas. a. Air sampling - Air samples are desired in order to measure the decay curve and carry out certain radio-chemical analysis, | It is important to know whether the radioactive material ■ near the cloud can be considered representative of a fission product mixture. Small samples of material' filtered from the air, which will be needed for this project are already being collected by the Los Alamos , group. No additional logistic support is needed for • this program. Laboratory work will be carried out in the same manner and by the same groups as for the ground BEST AVAILABLE COPY

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BEST AVAILABLE COPY Page 5 of Inclosure 1 1). Radiation field of the cloud - It is proposed to place film badges in the drone planes in order to obtain values of the total exposure which could have been obtained had they been manned. No additional logistic support is needed for this program, but it is important that the courses of the plane are known accurately in order to be able to interpret the results obtained. If ionization chambers are being used by the Los Alamos group to actuate their collectors, it will be desirable to include some means of obtaining a record of the radiation intensities encountered. Since this should not involve ary appreciable complications in instru mentation of the plane, it is suggested that this be undertaken by the group in charge of collecting the c. Particle size of the cloud material - At present no infor mation is available on the particle size of the radio active material in the cloud. This information is of vital importance for determining the efficiency of filters which might be needed as protection against inhalation of radioactive material. It is also im portant in estimating the danger from fallout of radio active material to the surface. Cascade irapactors are available from the Chemical Corps for collecting and separating the material into several particle size ranges. If necessary, the samples can be later measured by means of a microscope. These devices are extremely simple and require only a suction of one-half an atmosphere or greater. This can be easily obtained from the aircraft engine. These three projects on the radioactive cloud require little 'or no special logistic support and serve to provide answers to a number of questions or great importance to the Air Force. During the past six months the Air Forces have several times requested information on the nature of the cloud, and unfortunately only very rough answers have been available. This program should help to rectify this situation. a. At Bikini Doctor Penney exposed heat-sensitive papers by which with suitable calibration it was possible to measure the extent of the thermal radiation. These

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BEST AVAILABLE COPY Page 6 of Inclosure 1 measurenents are desirable to determine the importance of this radiation in relation to the other effects of an atonic bomb detonation* It is understood that additional samples of this paper are still available and it is proposed to distribute these at various distances. The logistic support for this project is negligible and the papers "will be distributed at the same time as the films for measuring gamma radiation. BEST AVAILABLE COPY