with a background of approximately 30 counts per have been written to relate urine assay data t minute. body content at a given time after contaminati Simpson gas flow proportional counters, acquired in May 1945, were operated originally with or at the time of contamination. an efficiency of 48 to 50 percent and a background one resorts to the convenience of computerizeca of about 1 count per minute. Modifications of these However, whe reduction and analysis or to hand calculations counters, chiefly lining the counting chamber it- practiced in the early days, the procedures ar self with electrolytic copper foil, reduced the based, at least in part, upon the systemic mod background to 0.15 + 0.1 count per minute. urinary elimination developed by Langham and c These counters, in continuous use until 1957, were sup- leagues.“ plemented in 1952 by four NMC gas flow proportional tained from studies of human subjects of short counters operating at 48 to 49 percent efficiency expectancy. with backgrounds of about 0.1 count per minute. The This model was derived from data ob These persons were given plutoniu citrate by intravenous injection in 1945.> La NTA procedure, adopted in January 1957, involved the used these data to derive a simple power funct counting of microscopic tracks instead of electronic equation to relate urinary excretion rate to b detection. This gave a background of 0.005 count per minute with an efficiency of 50 percent. The overall procedure had a sensitivity limit (50 per- content. The power function is often used to approximate a set of exponential functions cha acterized by both decreasing the amount and re cent confidence level) of about 0.05 disintegra- rate from various compartments. tion per minute per sample. yses of the data from the original patients an From April 1966 to More recent a January 1967, zinc sulfide scintillation counters from industrial exposures suggest that either were used; these devices were about 45 percent effi- power function or multiple exponential functio: cient with a background of 0.01 + 0.006 count per can be used to fit the observed excretion patt Minute. Although most of the human data were obtained Acquisition of alpha spectrometric equip-— ment in 1966 led to measurement of all samples by ing the first 140 days after injection, some alpha spectrometry after January 1967; the proce- information is available for excretion periods dure yields an efficiency of 27 percent and a back- to 5 years. ground of 0,004 + 0.003 count per minute. latter data give the following specific expres: In use Use of power functions based on t:! presently is an 8-detector system with electronic for rates of urinary and urinary plus fecal ex data processing capability, which allows one to tion in man given plutonium citrate over a per Measure simultaneously isotopes of 239-240), and 2420 of 5 years: 2 36p,, 2385, > ER. In addition to techniques such as alpha spec~ trometry and proportional counting, plutonium can be measured also in the urine by a track’etch procedure following neutron irradiation. ER = 0.002 t 0.74 ~’ = 0.008 t0°74, (Eq. (Eq. [In the lat- ter system, neutrons are used to produce fission where ER, and ER| fragments, usually in a thick plastic material injected dose exereted per day and t the days f supporting the plutonium-containing sample. lowing exposure. The damaged areas of the plastic are then etched and represent the fraction ot Following a single exposure at a known tin can be quantitated by use of optical means or spark one can estimate the body burden (Q) at time of counters .? exposure from measurement of a 24-hour urine sr Although not in wide use at present, this system is said to offer a considerable improve- men collected at a later time (t). Ment over others in terms of sensitivity. the relation ESTIMATES OF BODY BURDEN FROM BIOASSAY TECHNIQUES ER. = 0v/Q, Using Eq. 1 (Eq. Urine assay data are used as the basis for determining the body burden of internally deposited plutonium. 26 In more recent times, computer programs where U is the amount of plutonium measured in 24-hour urine sample at time t, then