47 used to supplement quantitative radiochemical analytical procedures, and has madepossible very rapid andpositive identification ofgamma-emitting radionuclides. The principles of in vivo gamma spectrometry as applied to human beings have been previously described.*’ Thesteel room constructed at BNL in 1957 for the Marshallese surveys has been described previously.® The “portable” 21-ton steel room, 5X5 100, Quartz Line Storage Pulse-Height Analyzer). Two complete detectors and analyzers with the necessary associated electronic circuitry were taken along,since considerable difficulty had been experienced during the previous year in maintaining the whole-body counting system operational under the conditions of tropical heat and humidity. Housing of the electronic equipmentin an air-conditioned, dehumidified room during x 6-ft with 4-in.-thick steel walls, was used to operation was of considerable assistance in main- with a 7x8» 10-ft air-conditioned wooden room, Since the principal photopeaks in these persons were knownfrom the previous study to be due to supply the required shielding (see Figure 49). This steel room was mounted on a large trailer along 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 sub- jects to be counted were brought aboard up the ship’s rampfrom the beach oneach islandvisited. Also available on the tank deck were shower facilities where each subject washed and then changed into an uncontaminated papersuit to avoid the possible risk of measuring any external contamination that might be present. A 3-in. NaI (TI) crystal (Harshaw) was placed over the subject at a distance of 19 in. above the apex of the chair (see Figure 51). The pulses from the photomultiplier were fed into a linear amplifier (Cosmic Radiation Lab. Inc., Model 101), and thence into a 100-channel analvzer (TMC-PA Cs'3" and Zn*5, and since the levels were sufh- ciently high, it was only necessary to count the subjects for 5 or 10 min with the particular geometrical arrangementdescribed above. The data were printed out on a papertape of a Victor add- ing machine, and the tapes were returned to BNL for analysis. Analysis of Gamma-Ray Spectra The quantitative interpretation of the gammaray 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 graphicalstripping method emploved,** °° the activity of the highest energy gamma-ray in the mixture, K*” (1.46-Mev), is determined directly from the cs'3” (0.66 Mev) COUNTS “5 MINUTES / 20 Kev CHANNEL taining its stability. ordinate valueofits total absorption peak. Then a channel-by-channel subtraction ofthe distribution et65 (Lt Mew) 4 1000 & [00 F corresponding to the abundanceofthis particular gamma-rayor radionuclide is made from the spectrum. Whenthis 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 of its peak. The distribution corresponding to the concentration of the second gamma-rayis then subtracted from theremaining distribution, and the process is continued with Cs'*" (0.66-Mev) until all the three major gamma-ray-emitting components have been deter- — oO a 0 O20 1 940 060 080 i090 ENERGY (Mev) 1.20 1.40 Figure 52. Gammaspectra of Marshallese male (subject 374, age 40, wt 70 kg - solid line) and normalized plastic phantom (containing 0.64 nC Zn®, 1.22 uC Cs’3”, and 140 g K - dashedline), 1959. 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