The 20-channel analyzer (Figure 2.9E) consisted of a scintillation detection unit, an amplification system and a multichannel pulse-height analyzer of the differential-discriminator type, using glow transfer tubes and fast registers for data storage. Two basic 10-channel units were operated together from a common control pane! to make up the 20 channels. Slit amplifiers for poth units furnished the basic amplitude-recognition function and established an amplitude sensitivity for each channel. The detection unit consisted of a 2-inch-diameter-by-2-inch-thick NalI(T1) erystal encased in Y, inch of polyethylene and joined to a photomultiplier tube. This unit was mounted in the top part of a cylindrical lead shield approximately 2 inches thick. A movable- sbelf arrangement, similar to that described for the end-window counter, was used to achieve mown geometries in the counting chamber, and a collimating opening Y, inch in diameter in the base of the shield was used for the more active samples. The laboratory on Site Elmer was used to gamma-countall IC trays and follow the gamma tonization and beta decay of selected samples. All of the instruments described for the YAG 40 laboratory were duplicated in a dehumidified room in the compoundat this site, except for the well counter and 20-channel analyzer, and these were sometimes utilized when the ship was anchored at Eniwetok. Permanent standards prepared at NRDL were used with each instrument. Operations such as sample dissolving and aliquoting were performed in a chemical laboratory trailer located near the counting room. Rough monitoring of OCC and AOC samples was also accomplished in a nearby facility (Figure 2.9F); this consisted of a wooden transportainer containing a vertically adjustable rack for a survey meter and a fixed lead pad for sample placement. Laboratoryfacilities at NRDL were used for the gamma-counting of all OCC and AOC samples, continuing decay and energy-spectra measurements on aliquots of these and other samples, and all physical, chemical, and radiochemical studies except the single-particle work performed in the YAG 40 laboratory. Each type of instrumentin the field laboratories, including the monitor- ing facility on Site Elmer, also existed at NRDL and, in addition, the instruments described be- low were used. Permanentcalibration standards were utilized in every case, and different kinds af counters were correlated with the aid of various mononuclide standards, U?™ slow-neutron fission products, and actual cloud and fallout samples. All counters of a given type were also normalized to a sensibly uniform response by means of reference standards. The doghouse counter (Figure 2.9G) was essentially an end-window scintillation counter with 2 Counting chamber large enough to take a complete OCC tray. It consisted of a detection unit containing a 1-inch-diameter-by-l~inch-thick Nal(T1) crystal and a phototube, which was shielded with 1/4 inches of lead and mounted over a 7-inch-diameter hole in the roof of the counting chamber. The chamber was composed of a %4-inch-thick plywood shell surrounded by a 2-inch-thick lead shield with a power-operated vertical sliding door. The detector was connected through a Preamplifier and amplifier to a special scaler unit designed for high counting rates. trays were decontaminated and placed in a fixed position on the floor of the chamber. Were counted with their '4-inch-thick aluminum covers in place. Sample All trays This instrument was used for basic gamma measurements of cloud samples and OCC, AOC,, and AOC,-B trays. The dip counter (Figure 2.9H) consisted of a scintillation-detection unit mounted on a long, metal pipe inserted through a hole in the roof of the doghouse counter and connected to the same amplifier and scaler system. The detection unit consisted of a 1'4,-inch-diameter-by-',-inchthick Nal(T1) crystal, a photomultiplier tube, and a preamplifier sealed in an aluminum case. This probe was positioned for counting by lowering it to a fixed level, where it was suspended by means of a flange on the pipe. A new polyethylene bag was used to protect the probe from contamination during each measurement. The sample solution was placed in a polyethylene con- fainer that could be raised and loweréd on an adjustable platform to achieve a constant probe pth. A magnetic stirrer was utilized to keep the solution thoroughly mixed, and all measure- ments were made with a constant sample volume of 2,000 ml. The instrument was used for famma measurements of all AOC, and water samples, as weil as aliquots of OCC samples of Inown fission content. _The Single-channel analyzer (Figure 2.91) consisted of a scintillation-detection unit, an amification System, a pulse-height analyzer, and an X-Y plotter. After amplification, pulses Om the detection unit were fed into the pulse-height analyzer. The base line of the analyzer 23