An Overview of Research in Radiation Biology and Protective Measures in the Manhattan Project During the War Years 1942-1946

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AN OVERVIEW O F RESEARCH IN RADIATION BIOLOGY AND PROTECTIVE MEASURES INTHE MANHATTAN PROJECT DURING THE WAR YEARS AND PROTECTIVE MEASURES

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The fission process in the nuclear pile was destined t o produce enormous amounts of radioactivity. These radioactive elements would, in turn, be emitting beta and gamma radiation of unprecedented levels. Radiation would also occur as a result of escaping neutrons which would be generated in the sustained fission process and would activate materials around the pile including elements contained in the air such as CO .The escaping fast and slow neutrons in themselves would also be sources of radiation.It was recognized a t once that various precautionary measures and some type of radiation limit would be required. Itis of historical interest that the physicists who were actively engaged i n advancing nuclear fission, immediately appreciated the nature and extent of the hazards and were already engaged in plans to introduce protective measures. In addition to this,they began to cast around for individuals who had experience in radiation and radiation biology who could provide enlightened guidance and might suggest other establish, ' with as much confidence as possible,the radio biological effects of the radio elements produced in the pile which might possibly enter the biological system. I n an effort to establish acceptable levels of radiation and the

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identification Of radiation limits,the various sections the Manhattan District and those actively engaged in radiation biology,naturally turned to the levels which had been previously identified as acceptable and were generally known as tolerance levels. The term " tolerance level" was a misnomer and is indicative of the fact that the hazards of radiation were not yet fully separated from other hazards such as those due to Extensive bibliographies exist on radiation hazards,limits and protection arising from the discovery and application of limits is of interest and will be briefly recorded here. The history of the development Of permissible Almost immediately following the discovery of x-rays and radium i n 1895, serious biological changes were observed i n exposed when a severe dermatitis was identified as a result of ionizing radiation.In the following year and by the end of 1896, many cases -- well over 6 0 -- were reported in the literature in which severe ski n- -. changes as a result of x - rays were recorded. By 1900, The first recorded effect was seen in January of 1896 i n view of the incontrovertible evidence of injury due to radiation, many voices were raised about protective measures. It is of.historic a1interest that as early as 1896, published statements were madewhich indicated that appropriate protective a3measures were necessary to avoid serious injury. From 1900 -cu until 1920, there was much discussion by many individuals *-2 about radiation hazards and the need for establishing radiation Q limits or protection guides,but official action was not

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In 1915, RUSS,a British physicist,presented a paper on protective no official aceion was taken to pursue radiation limits or This was read before the British Roentgen Society, but still There were a number of reasons why very little action was taken.First of all,the concept of a tolerance level was all - pervasive and this really suggested that there was some threshold level below which there was either full recovery or no significant or identifiable radiation although there was some lingering suspicion that perhaps very late effects might occur since very early - - in fact, by 1905 -- the blood-forming organs had been shown t o be especially sensitive to radiation as were the reproductive organs of Long term effects were either ignored or neglected t o appear with regard to some approach to establishing radiation protection measures and establishing some type of radiation limit or acceptable level. In1920the American Roentgen Ray Society formed a radiation protection committee. In1921. a British x-ray and radium protection committee was formed. In to publish suggestions as to the appropriate acceptable limit., 6 effects which could be fairly easily reproduced. In1924,c3

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Mut sc heller suggested that some limits based on the erythema dose in skin could be readily observed by many radiation dose was approximately 340roentgens and by appropriate calculation this proved t o be approximately ' .02rper day and was proposed asaso - called tolerance level. It turned out that his estimate of the erythema The Europeans, who generally made measurements with back scatter, that is,on the skin,were identifying the acceptable dose air -- for reasons of caution and also because they considered this level to be without level as .01 rper day, and this was the generally accepted figure for The Americans, since they measured it primarily in back scatter -- identified the radiation limits. The "Safe" levels were.essentially comparable. The International Congress of Radiology had made serious efforts to establish some type of acceptable limit. they had discussed the matter but had taken no conclusive action and simply deferred the matter to the next meeting three years group to make recommendations with regard to appropriate and acceptable levels of radiation. This committee was known as thex - ray and Radium Protection Committee. International Congress indeed submitted a report and this report in essence is quite comparable to the National Bureau of Standards Handbook 1 5 which was issued at that time with regard At that time they formed the first international

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to appropriate and acceptable limits.In1934, Handbook 2 0 of the National Bureau of Standards identified the tolerance level or acceptable level a s .1 rper day and pointed out that the Europeans used a level of .2rper day. It is this level of .1 rper day which was finally accepted - A number of events had occurred with regard to radium which clearly showed that serious hazards could result from radium which entered the body either by ingestion or other means and a number of repprts emanated from the radium dial industry in which clear evidence of radiation damage was established. It was therefore necessary to establish some limit for radium in take and in1941the National Bureau of Standards Handbook 27 identified the acceptable body burden as .1 of a micro curie of radium. Considerable literature existed since the work o f Robley Evans and others on injury and hazards due to t o radium and measurement of body burden levels. It should also be observed that during this time there was slowly coming to. recognition,although deeply submerged inthe general question of radiation biology,the idea that late effects might begin to appear. genetic changes were identified unequivocally in lower The work of Muller and others in which -organisms had great influence. The findings suggested that some N biological effects were non-threshold. On the whole, though, this3

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concept received relatively little attention and the various projects of the Manhattan Project essentially operated on the levels established by the various committees and the Handbooks of the Bureau of Standards.It should be noticed that these handbooks had actually no official status,but were believed $0 be reliable and had a fairly rational basis. A gamma ray and x-ray level of adopted as an acceptable level. for all types of radiation including internal emitters and heavy particles such as protons,neutrons and alpha particles. At this early date there was indeed recognition of the greater biological effectiveness of high-LET radiation and a factor of 1 0 was introduced for heavy particles. The tolerance level was considered to be 1 / 10that of gamma radiation and identified .1 rper day was therefore This eventually became standard Although permissible levels which prev a ii ed were .1 rper day, there was continuous debate as to whether these limits should not be lowered and there was much discussion as t o whether indeed .1 rper week would not be a more appropriate level. This debate continued but no concerted effort was made to rigorously reduce this official level because of the exigencies of the war and the robust effort that the Corps of Engineers wished t o pursue inthe development of nuclear fission. However, cautionary statements were prevalent that unnecessary exposure should be avoided. or minimized.

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~ ~ a ~ uva ,-;:>ether it be gut, lung, bono, eke In the i'ollowing te ble aro listed ccncentretdoas in o m or ciiother tissuc I

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Nagging uncertainties were the result of statements in Handbook 2 0 which was referred to earlier,in which the following provisional and it is advisable to apply generous safety "The tolerance dose of .1 rper day i s A radiation protection manual issued through the ,University of Chicago stated as follows : "It must be continually borne in mind that the tolerance dose isthe assumed maximum that can be endured without effects. It is not to be taken asthe optimum t o which one should expose themselves. exposure anyone gets,the better it is for him. " I n May 1943there was a reasonably clear understanding of the hazards of internally distributed radioactive elements,Since hazard limits had t o be established promptly the levels for the various radio elements were generally developed by calculation -- t o be modified later by any serious discrepancies discovered by energy absorbed per unit mass of biological tissue modified by the best estimate of the distribution of that particular radio element.Calculation of energy absorbed was translated into rad s.A table is reproduced for historical interest to indicate that such acceptable or tolerance levels were indeed identified and that fairly substantial measures were taken to introduce appropriate radiation limits. Estimates of the metabolic behavior of these various elements were based largely on the research activities carried out at

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the University of California and at the University of Chicago where these metabolic studies on the fission products were pursued. Essentially simultaneously, the University of Rochester pursued related research on biological effects of internal and A brie d number of reports pertaining to radiation protection and radiation limits are hereby identified and a brief discussion of their contents is indicated. The major source of radiation, of course, would be the nuclear fission process.' As the piles were developed, first at the University of Chicago, later at the Clinton Laboratories and eventually at Hanford, Washington, the initial and primary reviews of radiation hazards were therefore made at the Metallurgical Laboratory at the University of Chicago. Potential hazards engaged a major prot ion of the attention of the scientific group - and from the beginning a radiation physicist was assigned tothe general problem of radiation hazards. of the Metallurgical Laboratory and the Manhattan Corps of Throughout the records Engineers activities,there was continuous reporting of the levels of radiation in working areas,constant examination of the means of assessing the radiation hazards,studies on radiation measurement, development of radiation measuring equipment and specific statements on radiation protection measures under A number of reports are cited which indicate the various

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approaches to hazard assessment, the manner i n which attempts were made to calculate radiation doses and the general tenor tissue,using .1 r as an acceptable level. The first concerted effort to prepare regular reports was begun inthe middle of 1942. July9,1942 by Sol Wexler and C. E. Boyd, records the A report on uranium poisoning issue d_-- information available in the literature on the general nature of the chemical hazards of uranium and the pathological manifestations of uranium poisoning. the fact that uranium inthe form of uranium oxide (U08, U02or UO3)could enter the body by inhalation or through contact with certain soluble salts. The abstract identifies The review reports the pathological manifestations to be nephritis and the anatomical and functional disturbances are the result of accumulation of the uranium inthe kidney a s attempts are made at excretion. is pointed out as efforts to limit ingestion and contact, and of course,avoiding inhalation of the agent. On the15th of August, 1942,a report exists in which Ernest 0. Wollan indicates that personnel were being monitored by