The LASL Low-Level Monitoring Program

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TBE LASL IBW-LEVEL MONITORING PROGRAM Since th8 spring of 1956, 8 program of routine monitoring of t h e radioactivity of people and foodstuffs hra been carried out at the Los Alamos Scientific Laboratory. This program hnd ito origin in the liquid scintillation counting research of the Bealth Division. The large-volume detectors developed for the neutrino studies proved to be admirably adapted to the rapid measurement of the natural K-40 activity of people and foods, in spite of the extremely lor level of this activity. curie of IC-40,) The sensitivity of the instrument for unnatural gamma activity is 0.001 pc, which io 100 to 1,OOO time8 smaller than the m8ximum permissible concentrations of gammr-emitting fission products c . in the body. The aims of the program are: > L 1. To measure the natural gamma activity of people fission product Cs-137; rad 3. To look for other gam8 emitters which m8y from due to the time to time The natural radioactiolty of thingg I s of considerrble interest because of our lack of knowledge of the possible effects of very low levalo of radiation. A study of the sources of the m u r a l radirtion

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dose and tbetr variations appears to be one of the more promising methods of obtaining this informatfon. Cs-137 from fallout is almost certainly not a significant hazard compared with Sr-BO; however, it is Important that accurate Information be available on Its distribution and concentrations so that one can be sure it can safely be ignored. Furthermore, information obtained on the behavior of t h i s activity (which is comparatively easy to measure) will be of considerable help in the understanding of the basic mechanisms involved in the distribution not only of fallout from weapons tests but also may be 8pplicable to some extent to the . problems of reactor waste disposal. Certainly the instrumentation and sampling systems will be useful for either problem. Although no other fission products are known to reach man to the extent that Sr-90 and Cs-137 do, the confirmation of their absence is very Important. While Project Sunshine set up a very Intensive and extensive program of Sr-90 monitoring, there was no comparable program In existence for the study of total gamma contamination. The unique qualification of the large-liquid scintillation detector for this program is the extreme speed of sample counting. The natural radioactivity of man can be measured to 8 precision of 5% in less than 4 minutes of counting time. Large samples of foodstuffs (e.g., 50 to 100 pounds of dry milk solids) can be assayed in comparably short times without any chemical treatment, The method Is conpletely nondestructive and thousands of samples can be measured per

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During 1957, the USL program measured weekly milk samples from 21 points and monthly samples from 12 additional points in the United States. Some 40,000 pounds of dry milk passed through the counter,along with 3,000 gallons of fresh milk,a totalof nearly tions on dried blood samples (25 tons) from 20 locations and 800 measurements of the radioactivity of people were made. I n spite of the comparative isolation of Los Alamos, it was possible t o measure people from 34 of the 48 states i n 1957 and 28 out of 48 I n 1956. The correlation of the Cs-137 content of people and of their food- . stuffs is excellent.This program occupied the counter less than 30% of the time ; the rest of its schedule being used for the study of the metabolism of gamma-emitting nuclides In dogs, monkeys and man and for the investigation of clinical applications of the instrument. The results of this program are being reported inthe open literature (refs ). They are very encouraging in that they confirm the relative unimportance of the fission products other than Sr-90 as limiting hazards. in addition to Ce-137, but their levels are very low and the duration of the exposure very short. Ba-140 and 1-131 have been noted occasionally, Even Cs-137, t h e most abundant and pers is tent, is present at a level 20 times smaller thn ' that of the naturally radioactive isotope of potassium, K-40. Tbe latter in turn contributes only about 20% of the total natural background radiation s m a l l amount of Cs-137 from the much larger amount of K-40. The principal problem inthe measurements is picking out the

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contamination from the natural radioactivity of the radium series can mask the Cs-137. The milk sampling network will be extended in 1958 to give better coverage of the entire United States. I t was hoped that the aonitori n g of dried blood would provide a simple and cheap method of following the activity of the country's meat supply, but the processing methods used in the preparation of the blood (it is intended for fertilizer and animal f e e d ) are such as to permit too much chance contamination, with the result that the numbers are too erratic to be interpreted. Milk, on the other hand, is processed under sterile conditions and shows no evidence of external contamination. The coverage of the human population will be greatly increased by the completion during 1958 by the Army Medical Corps of a similar installation at the WRAIR, Washington. population be accessible, but returning military personnel from overseas Not only will a more cosmopolitan will provide subjects from outside continental United States.