23 Findings. 7 Tit TTT MAY 1958 — (TOTAL 32.540 GPM) MARCH 1958 v7(TOTAL 1.213 CPM) L o CHANNEL WIDTH 0,020 Mev ! ! O02 0.4 : | O6 8 1,0 Le 1.4 GAMMA RAY ENERGY IN Mev 1.6 18 removal of unnecessary articles from within the room were ineffective, indicated that the con- ethph ph COUNTING RATE / GHANNEL IN CPM u Figure 16. Background counting rates at Rongelap Atoll. CHANNEL WIDTH 0.20 Mev \ 02 ! ' 0,4 06 O08 10 L2 GAMMA RAY ENERGY IN Mev 1.4 16 18 2.0 Figure 17. Rongelap subject +50, May 1958, total 43,260 cpm above background. : (0000 =F z O00E 4 Zz = F ° ev. . S 100e 22 kev 3 | i q ? F CHANNEL WIDTH} = 1 MAY 1958 9° ¥ — 4 =+ 4 ce? MARCH 1957 3 . ~ Ee a z E = 2 OE =3 ; ef gz 4 FE 2 c ir ° 0.2 0.4 0.6 08 1.0 2 GAMMA RAY ENERGY IN Mev 14 5901 + . a! Figure 18. Rongelap subject +79. total 66,974 cpm above background (analysis No. 4). c Ee a ° Figure 16 compares the background gamma-ray spectrum of March 1958 with that of May1958. (A few backgrounddata, plant and marine specimens, and data on one of the American subjects had been carried separately and hence were not lost at sea.) In additionto its being high, the Mav background showsa peak at 1.6 Mev, which wasattributed to Ba-La'*®. Except for this one peak, the background spectrum is essentially continuous. This, plus the fact that external procedures wereeffective in reducing the background, whereascleaning the inside of the steel room and 1000 TTT COUNTING RATE / CHANNEL IN CPM 10000 taminating radioactivity was outside the room. Figure 17 shows the net gamma-ray spectrum of a representative Marshallese subject after appropriate correction for analyzer dead time and subtraction of the background. The Cs'*' and Zn** peaks are seen to be prominent, and in this case there is also a net peak at 1.6 Mev which has been attributed to Ba-La'" and which obscures the K‘* peak. The latter was not a constant finding, but even in the spectra without it, the K*" peak was usually obscured by the high background. It had been hoped that the spectra could be examinedfor other peaks, but, since the method of analysis re- quires the high energy peaks and their associated Compton scattering spectra to be subtracted out first, the difficulties introduced by the high background,the 1.6 Mev peak, and the masking of the K"peak renderthe entire procedure very uncertain. Similar difficulties prevented examination of the spectrum for possible contributions from Sr’? bremsstrahlung. If future surveys show the presence of additional nuclides, the 1958 data may be re-examined. For the present, however, only the Cs**? and Zn* values, based on peak heights, are reported here. Figure 18 shows the spectrum for another subject in 1958 comparedwith his spectrum in 1957. Becauseof the narrower channel width used in the 1958 study, the activities are even higherrelative to the 1957 levels than the graph indicates. The body content of Cs'** and Zn*® and the urinary concentrations of Cs'*", Zn®, K'°, and Sr®° are presented in Table 15. Since the urine specimens were obtained in March, they maynotcorrespondstrictly to the body data obtained in May. The subjects are divided into groups on the basis of their island of residence. The data are presented in this wayrather than on the basis of exposure