Availability of Radioactive Isotopes (Science, June 14, 1946, Vol. 103, No. 2085, PP 697 - 705)

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-7Reprinted from SCIXNCE,'June 14, 1946, Vol. 103, KO. 2685, pages oY7-705. Announcement From Headquarters, Manhattan Project, Washin PEUTIC RADIOISOTOPES has been herP alded as one of the great peacetime contributions of the uranium chain-reacting pile. This use of the pile wiy unquestionably be rich in scientsc, medical, and teehnological applications. Manhattan Project scientific, technical, and administrative personnel have, since the inception of the pile, been cognizant of its peacetime potentialities and have, since the end of the war, been active in attempting to realize these opportunities. Since, however, mar-built piles and wartime researches had other objectives, a considerable transition in researches, developments, and operations connected with piles must be effected before the supply of radioisotopes can begin to meet the demand. (1)A pile cannot make the extensive variety of radioisotopes producible with the cyclotron because the cyclotron makes use of a much greater diversity in energy and type of nuclear bombarding projectiles. Present piles are copious sources of low-energy neutrons, ahich Can give rise to large yirlds only of isotopes produced by (n,f) and (n,y) processes. (2) Although large numbers of radioisotopes a r e produced in abundance by the fission of uranium in the piles, their availability is limited by the difficulties encountered in isolating them. It has not yet been found feasible to remove individual hsion products from waste solutions of the plutonium extraction process. Most of the fission products being made available are not salvaged by-products of the plutonium process but are in each case Stems requiring special production from unprocessed irradiated (3) Most of the radioisotopes in greatest demand, such as C 14, S 35, and P 32, must be produced by the irradiation of materials foreign to the pile. Existing piles mere not designed f o r this purpose. (4) Although a pile i s a copious source of neutrons, it is not a limitless source. It is possible to load a pile f o r nonfission product radioisotope production only u p to the limit at which so many neutrons are absorbed in the introduced material that the chain reaction ceases even though the control rods are withdrawn as f a r as feasible. With available pile facilities, this limit does not permit the production of a sufficient quantity and quality of many radioisotopes to meet anticipated national demands. To accomplish ' this it would very likely be necessary to build piles especially designed f o r the purpose. (5) Technical problems involved in the irradiation of some materials have been, and mi11 continue t o be, responsible f o r delays in making certain isotopes available by routine irradiation. Examples of such problems are: (a) proper canning of the material to prevent rupture of the container by its internal action o r by the external action of the coolant, with consequent loss of the material and damage to the pile; (b) dareful purification to prevent loss of neutrons by absorption in impurities as well as undesirable radioactivity in the irradiated material; and (e) proper distribution of the material throughout the pile to prevent local overheating o r undesirable regulation characteristics of the pile. ORGANIZATIONEQR ALLOCATIOXAND DISTRIBUTION In accordance with the established custom of the Manhattan Project of seeking competent outside advice and aid on vital scientific matters, such as nonproject distribution of isotopes, Maj. Gen. L. R. Groves asked the president of the National Academy of Sciences to nominate a representative committee of outstanding scientists to recommend policies and aid in establishing arrangements fora desirable distribution of those tracer and therapeutic isotopes available from Manhattan Project facilities. An interim Advisory Committee on Isotope Distribution Policy was formed, two representatives being chosen from each of the major fields of isotope application: Physics-Lee A. University of Rochester, and president-elect of California Institute of Technology, Pasadena ; and Merle A. Tuve, head, Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, D. Crellin Chemistry Laboratories, California Institute

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of Technology; and Vincent du Vigneaud, head of the Department of Biochemistry, Cornell University Medical College, New Pork City ; Medicine-Cornelius P. Ehoads, director of Memorial Hospital, New Pork City, and chairman of the Committee on Growth of the National Research Council; and Cecil J. Watson, head of the Department of Medicine, University of MinneE. Zirkle, professor of botany and director of the Institute f o r Biophysics and Radiobiology, University of Chicago, Chicago, Illinois; and A. Baird Hastings, head of the Department of Biological Chemistry, Harvard University Medical School, Cambridge; Applied Chemicals Department, General Electric Company, the Radioactivity Section, National Bureau o f Standthe Isotopes Branch, Research Division, Manhattan District, was chosen acting secretary to coordinate the efforts of the Committee and to effect liaison with the The recommendations of this Committee on a suitable interim mechanism for allocation and distribution have been adopted v3hout modification. This mechanism is as f olloivs : (1)All requests will be submitted to the Isotopes Branch, Research Division, Manhattan District, .where each request will be reviewed with regard to all technical questions affecting the requester and the Project. This initial review will be made by a group of seientists in the Project who have had much experience in the production of radioisotopes and in technical matters concerned with their use. (2) Nonproject requests will then be referred to an Advisory Subcommittee on Allocation and Distribution, which has been appointed by Gen. Groves on the nominations of the Distribution Po1ic.v Committee. This Subcommittee will have the responsibility of advising on the allocation and distribution of isotopes according to the scientifk value of the intended application and the qualifications of the requester. It will operate under the supervision of the Distribution Policy Committee and in conformity with its approved policies. I t s members are: E. T. Bainbridge (3) Each request for material for use i n human beings will be referred by the Subcommittee on Allocation and Distribution to a Subcommittee on Human Application, which was similarly nominated and appointed. This Subcommittee mill have final veto power on any distribution suggested f o r human application. I t s members, chosen from among radiologists and clinicians experienced in radioisotope uses, are : Andrew H. Doady, University of Rochester, sity; G. Failla, Columbia University. ( 4 ) Small Panels of Consultants, nominated by the Policy Committee from a number of specialized fields of possible isotope application and from various regions of the Sation, mill be available as advisers on scientific matters connected with requests. (5) Manhattan Project personnel have not been excluded from membership in any of the nonproject advisory groups. I n many cases their membership has been strongly advocated by the Distribii: ion Policy (6) Effective liaison mill be maintained between the Isotopes Branch of the Manhattan District Research Division, which initially receives and finally effects distribution on nonproject isotope requests, and the associated advisory groups whose functions are set PRINCIPLESOF ALLOCATIONAND DISTRIBUTION In establishing initial policies on the distribution of scarce materials, the criterion used has been the maximum benefit to the national welfare, due consideration being given to the limited amount of available mate- (1) Isotopes will be made available to individuals only through qualified institutions. The administration of the institution will make the necessary financial and legal arrangements, but the material will be allotted for the uses specified in the request. (2) Secondary distribution of isotopes will not be sanctioned unless indicated and authorized under the original request o r subsequently in vi-riting through the accepted channels f o r requests. (3) The initial order of priority adopted f o r the allocation of materials and of production effort is established according to intended use of the material, as follows: (a) publishable researches in the fundamental sciences, including human tracer applications, requiring relatively small samples ; (b) therapeutic, diagnostic, and tracer applications in human beings and publishable researches in the fundamental sciences requiring larger samples ; (c) training and education by accredited institutions in the techniques and applications of radioisotopes; and (d) publishable researches in the applied sciences. Allocation of material f o r researches which are not to be published or f o r routine commercial applications P;as considered by the Distribution Policy Committee not to fall Tithin its responsibilities. Allocation f o r routine commercial The initial policies adopted are :

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applications will be deferred until experience is gained with supplying the research needs previously mentioned. Special groups may then be established to advise on such allocation. As indicated in the section on availability, none of the separate purified radioisotopes is in routine operational production. In some cases research groups have progressed only to the point of investigating how irradiations can best be performed to create a given isotope and how to isolate the isotope in small amounts. I n other cases methods are under investigation i n development groups for increasing the scale of irradiation and chemical processing. I n a few eases it has nom become possible to start placing irradiations and chemical processing into the hands of technical operations groups f o r routine ‘bproduction.” Research into methods of small-scale creation of most of the isotopes took place widely before the establishment of the Project; since then, it has been carried on extensively by project laboratories engaged in nuclear research. Thus, crcdit f o r the results of research on radioisotopes is shared by many nonproject and project personnel. Most of the research within the Project in this regard has been done by nuclear physics and radiochemistry groups a t Clinton Laboratories a t Oak Ridge, at the Radiation Laboratory of the University of California, and a t the Xetallurgical and Argonne Laboratories of the University The present ‘Lesperimental-lotproduction” has been carried on largely by the Clinton Laboratories, which since July 1945 have been administered by the Monsanto Chemical Company. I n the case of several isotopes in great demand, the Argonne Laboratory has cooperated in preparing materials in proper form f o r irradiation at Hanford and in testing the results. The Du Pont Company, operators of the Hanford Plant, has cooperated in making irradiations of materials possible at Hanford. The Monsanto Chemical Company has agreed to initiate the routine production of nationally demanded radioisotopes and to distribute them from the Clinton Laboratories under A Manhattan Project Technical Advisory Committee on Isotopes has been active in maintaininq liaison between major laboratories of the Project on (1)production and distribution matters concerned with the national distribution program and (2) developments in radioisotope techniques and applications. This and R. E. Zirkle, of the Argonne and Netallurgical Connick, of the University of California Radiation Laboratory; J. H. Manley and It. Taschek, of the Los Alamos Scientific Laboratories; and, in regard to Larson, of the Tennessee Eastman Corporation, Oak Radioactive isotopes are created in chain-reacting piles by two processes : (1)the fission of U 235 nuclei, which maintains the chain reaction, and (2) neutron absorption by nonfissionable nuclei placed in the pile products”--exist as a mixture of many radioactive species, each free of sip scant amounts of stable (carrier) isotopes, in a large amount of the parent substance, uranium. The desired radioisotope must subsequently be separated from uranium and from the other fission products, as well as from any neptunium and plutonium formed by neutron captnre in U238. I n the chemical process actually used, the fission products are separated from the mixture either as individual radioactive species or as groups of species (Col. The methods now in operation f o r the preparation of fission-product radioisotopes were developed to meet certain definite specifications, which in turn mere set by the biological work in which the radioactive materiaIs were to be used. These specifications called f o r 0.1-1.0 curie2 amounts of each of the major fission mg./curie) form, and radiochemically pure (> 9098 per cent, depending on the species); smaller or less pure amounts of minor species were also required. The radiation intensities involved in working with mixtures of fission products at the curie level required the invention and use of chemical processes which were remotely controlled from behind specially constructed lead and concrete barriers and were economical of material. F o r these reasons the existing processes and equipment are not suited to isolate fission products in forms radically different from those listed. However, since these methods permit the isolation without carrier of nearly every fission product of half-life from 1 week to 30 years and occurring in significant amount, this inflexibility is not considered to be a handicap. l Only those radioisotopes of half-life greater than 12 hours

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700 SCIENCE Vol. 103, No. 2685 Those fission-product radioisotopes which can now temporarily or indefinitely delayed in fulfillment. The be isolated3 from pile uranium in moderate quantity activity stated in this column is related to the figures and good quality without added carrier are listed in giving volume and other characteristics of the prepaTables 1, 2, and 3. I n Table 1 are given also the latest data on half-life and radiation energies for The letters in the column headed “ C l s s ” are an each radioelement involved and also the properties of attempt to indicate approximate availability and have daughter radioisotopes which will be present. The the following meanings: A: usually on hand (long sentially the amount which m y be supplied at one seldom on hand; produced on experimental basis only; tim; requests for more tlian this amount m y be D : not on hand; can be done but with difficulty.i ati ‘ 8 I t must be emphasized that no routine production system Inasmuch as a routine production system, with yet exists. The radioisotopes being made available a t this time are the results of research and development proceedlngs. tendant control and standar&, does not exist,

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a s of radwchernical or chemical purity o r To obtain an isotope of this kind involves the inchemical separation process on the active material dl (Derived from products in Table 1) Probable mas. unit SolidsSource Radio- radioactive quantity Carrier present solvent Volume Class See Table 6. t Depends on purity required and age. In Tables 4-6 are listed those neutron-induced radioisotopes of half-life greater than 12 hours which are known or believed to be producible in the pile. (By-products usually on hand in impure form) See Table 1 for radiation characteristics of isotopes reactions (Table 4). The most prominent reaction is simple neutron absorption, yielding a radiozctive element isotopic with the parent element. This is the mutation and fission reactions in that cairier-free material is not produced (except in those few cases where a radioactive chain is begun). be done prior to shipping (hence the term “service irradiation” to describe such an activation). I n order to utilize the available facilities most efficiently, these materials will be exposed in the same containers in which they will be shipped, and only certain quantities dl be irradiated. Therefore, those radioelements supplied without processing will be available only in units which are 1, 0.1, 0.01, and (sometimes) 0.001 part of the guaetita’es listed under “Approdmate mu …