These pulses are amplified then analyzed according to peak voltace and counted. Nal(Tl) crystals are in wide use today as cammaray detectors because of their high efficiency and linearity. The disadvantase of tneir beings nysroscopic is larsely overcome by sealing them hermetically in thin-walled aluminum containers. For this experiment a special sample holder was made for the spectrometer which allowed the bottoms of the sample containers to be placed 2 inches above the top of the collimator (a 1/2-inch hole through 6 inches of lead) and centered witnout further adjustment. The 4-inch in diameter by 4-inch long NaI(T1) crystal, 5-inch Du Mont vhotomultiplier tube, preamplifier and housing (Fig. 1) were the same as those used in the analy- sis of the data from Operation TEAPOT? and are more fully described elsewhere. * The output of the preamplifier was fed into a Tracer- lab non-overloading linear amplifier whose output pulses were analyzed by an Atomic Instrument Company Model 510 pulse heicht analyzer, me) the variable base line bias of which ott eee ee — —— was provided by a helipot, motor driven through its renge.®© The output pulses from the analyzer 4 were fed into