47 spectrometry as applied to human beings have been previously described.*’ Thesteel room constructed at BNL in 1957 for the Mafshallese surveys has been described previously.* The “portable” 21-ton steel room, 55 x 6-ft with 4-in.-thick steel walls, was used to supply the required shielding (see Figure 49). This steel room was mounted on largetrailer along with a 78 10-ft air-conditioned wooden room, designed to house the electronic components of the counter (see Figure 50). The trailer was mounted on the tank deck of the Navy LST, and the subjects to be counted were brought aboard up the ship’s ramp from the beach on each island visited. Also available on the tank deck were shower facilities where each subject washed and then changed into an uncontaminated paper suit to avoid the possible risk of measuring any external contamination that might be present. A 5-in. NaI (Tl) crystal (Harshaw) was placed over the subject at a distance of 19 in. above the apex of the chair (see Figure 51). The pulses fom the photomultiplier were fed into a linear amplifier (Cosmic Radiation Lab. Inc., Model 101), and thence into a 100-channel analyzer (TMC-PA COUNTS /5 MINUTES / 20 Key CHANNEL 10,000 ¢ AR , 1 taken along,since considerable difficulty had been experienced during the previous year in main- taining the whole-body counting system opera- tional under the conditions of tropical heat and humidity. Housing of the electronic equipmentin an air-conditioned, dehumidified room during operation was of considerable assistance in main- taining its stability. Since the principal photopeaksin these persons were known from the previous study to be due to Cs'*7 and Zn**, and since the levels were sufficiently high, it was only necessary to countthe subjects for 5 or 10 min with the particular geometrical arrangement described above. The data were printed outon a paper tape of a Victor adding machine, and the tapes were returned to BNL for analysis. Analysis of Gamma-Ray Spectra The quantitative interpretation of the gamma- ray pulse-height data for the discrete gamma energies involved the graphical reduction of the data. A typical spectrum of a Marshallese is shown in Figure 52. The ordinate represents counts per 20-kev pulse-height increment, and the abscissa represents gammaenergy. In the graphical stripping method employed,**** the activity of the highest energy gamma-ray in the mixture, K*° (t.46-Mev), is determined directly from the cs!37 (0.66 Mev ordinate value ofits total absorption peak. Then a channel-by-channel subtraction of the distribution 7 857), 12 Mev) 1000 F corresponding to the abundance ofthis particular gamma-rayor radionuclide is made from the spectrum. When this subtraction is completed, the concentration of the gamma-ray of the next highest energy, Zn® (1.14-Mev) can be estimated from the ordinate value ofits peak. The distribu- tion corresponding to the concentration of the 100 F (1.46Mevy) second gamma-ray 1s then subtracted from the re- maining distribution, and the process is continued with Cs'?? (0.66-Mev) until all the three major gamma-ray-emitting components have been deter0 Q | 1 i 020 040 060 1 080 1. 100 oh 1.20 1.40 1.60 ENERGY (Mey) Figure 52. Gamma spectra of Marshallese male (subject #4, age 40, wt 70 kg - solid line) and normalized plastic phantom (containing 0.64 nC Zn*, 1.22 uC Cs'*’, and 140 g K - dashed line}, 1959. ‘ 1 + ‘ ‘ mined.” This stripping processis illustrated on a spectrum of the plastic phantom containing known amounts of K*°, Cs'**, and Zn* (Figure 53). It is to be noted that at the concentrations used here (approximately the mean concentrations found in the Marshallese), the Compton contribution of a od Mp» rapid and positive identification of gamma-emutting radionuclides. The principles of mn vivo gamma 100, Quartz Line Storage Pulse-Height Analyzer). Two complete detectors and analyzers with the necessary associated electronic circuitry were a. used to supplemeng.quantitative radiochemical analytical procedures,and has made possible very