Lat49, Accordingly, a chemical separation of Ral40 way made from a fallout sample. Nine days after the separation, Ral40 had come to transient equilibrium and a scintillation spectrometer pulse-height distribution was obtained. This distribution was used in the analysis of all the fallout spectra. Upon subtract ion of the Bat4O and Lal40, a peak at about 750 kev was fournde Since Zr?5-Nb9> vielded only one maior photo-peak at about 750 kev with only an insignificant peak at 235 kev, a standard curve for Zr95<-Nb95 was obtained and a subtraction procedure similar to that for Bal40-La140 was used. Similarly, a peak ak 500 kev was found after the subtraction of Bal40-Lal40 and Zr95-Nb95, This peak was assigned to Rul03, A standard curve was also obtained for Rul03, Two standard spectrometer curves at the two amplifier gains used for the fallout spsctra were obtained for each of the isotopes mentioned. At gamma-ray erergies of a few hundred kilovelts or mre, two pulse-height distributions per gamma ray are obtained, a bell~shaped distribution called a photo~peak and a broad, nearly flat, distribution due to Compton effect. At lower energies the amount of Compton effect becomes increasingly small compared to photo-effect,soe that at about 100 kev the Compton effect is negligible, In addition, there are secondary scattering effects which throw counts normliy in the Compton distribution into the photo-peak which for low gamma-ray energies results in a great reduction in the theoretical Compton dis- tribution. This effect is illustrated in Fige 3.26 by ihe theoretical and experimental curves of the ratio of the vhoto-peak to total area. At the low gamma-ray energies the procedure was to work first with the highest energy photo=peak left from the subtraction of known isotopes. The photo-peak was fitted with a Gaussian curve and its area determined. The Compton effect is found from the experimental curve of ratio of photo=peak to total peak. The Compton distribution was then subtracted from the peaks cf lower energy and the procedure repeated. At enerpies below about 200 kev the photo-neak of the various gamma rays overlapped. As an aid in the subtraction procedure it was assumed that the width of the peaks at one-half maximum followed the EE law, 18/ where E is the energy of the gamma ray procucing the photo=peak. Thus, three conditions were imposed upon the phcto-peaks, (1) all available counts were used, (2) the peaks were Gaussian in shape, and (3) the width of the peak followed the E} law. 3483 Detection Effictency of the Scintillation Spectroreter Assume that the gamme-ra3y source emits gamma rays of one energy only. The number, Ny, of these gamma rays detected by the crystal are N= NoeME NArKar ( . oe nar iva) . where = source strength 79 (3222)