The survey-meter readings were used to establish the gamma-ionization decay above a surface approximating a uniformly contaminated infinite piane. 2.2.4 Laboratory Facilities. Samples were measured and analyzed in the shielded laboratory aboard the YAG 40, the field laboratory at Site Elmer and the U.S. Naval Radiological Defense Laboratory (NRDL). The laboratories in the forward area were equipped primarily for making early-time measurements of sample radioactivity, all other measurements and analyses being performed at NRDL. Instruments used in determining the radiation characteristics of samples are discussed briefly below and shown in Figure 2.9; pertinent details are given in Section A.2, Appendix A. Other special laboratory equipment used during the course of sample studies con- sisted of an emission spectrometer, X-ray diffraction apparatus, electron microscope, ionexchange columns, polarograph, flame photometer, and Galvanek-Morrison fluorimeter. The YAG 40 laboratory was used primarily to make early-gamma and beta-activity measure- ments of fallout samples from the SIC trays. All trays were counted in an end-window gamma counter as soon as they were removed from the elevator; decay curves obtained from a few of these served for corrections to a common time. Certain trays were examined under a widefield stereomicroscope, and selected particles were sized and removed with a hypodermic needle thrust through a cork. Other trays were rinsed with acid and the resulting stock solutions used as correlation and decay samples in the end-window counter, a beta proportional counter, a 4-7 gamma ionization chamber and a gamma well counter. Each particle removed was stored on its needle in a small glass vial and counted in the well counter. Occasional particles too active for this counter were assayed in a special holder in the end-window counter, and a few were dissolved and treated as stock solutions. Gamma-ray pulse-height spectra were obtained from a Selection of the described samples using a 20-channel gamma analyzer. Sturdy-energy calibration and reference-counting standards were prepared at NRDL and used continuously with each instrument throughout the operation. The end-window counter (Figure 2.9A) consisted of a scintillation detection unit mounted in the top portion of a cylindrical lead shield 1Y, inch thick, and connected to a preamplifier, amplifier and scaler unit (Section A.2). The detection unit contained a 144-inch-diameter-by-'/,- inch-thick Nal(T1) crystal fitted to a photomultiplier tube. A / -inch-thick aluminum beta absorber was located between the crystal and the counting chamber, and a movable-shelf arrangement was utilized to achieve known geometries. The beta counter (Figure 2.9B) was of the proportional, continuous-flow type consisting of a gas-filled chamber with an aluminum window mounted in a 1'4-inch-thick cylindrical lead shield (Section A.2). A mixture of 90-percent argon and 10-percent CO, was used. The detection unit was mounted in the top part of the shield with a l-inch circular section of the chamber window exposed toward the sample, and connected through a preamplifier and amplifier to a conventional scaler. A movable-shelf arrangement similar to the one described for the end-window counter was used in the counting chamber. Samples were mounted on thin plastic film stretched across an opening in an aluminum frame. The 4-7 gamma ionization chamber (GIC) consisted of a large, cylindrical steel chamber with a plastic-lined steel thimble extending into it from the top (Figure 2.9C). The thimble was sur- rounded by a tungsten-wire collecting grid which acted as the negative electrode, while the chamber itself served as the positive electrode. This assembly was shielded with approximately 4 inches of lead and connected externally to variable resistors and a vibrating reed electrometer, which was coupled in turn to a Brown recorder (Section A.2). Measurements were recorded in millivolts, together with corresponding resistance data from the selection of one of four possible scales, and reported in milliamperes of ionization current. Samples were placed in lusteroid tubes and loweredinto the thimble for measurement. The gamma well counter (Figure 2.9D) consisted of a scintillation detection unit with a hollowed-out crystal, mounted in a cylindrical lead shield 14 inches thick, and connected through a preamplifier to a scaler system (Section A.2). The detection unit contained a 1%, -inch-diameter- by-2-inch-thick Nal(T1) crystal, witha ¥,-inch-diameter-by-1'4-inch well, joined to a phototube. Samples were lowered into the well through a circular opening in the top of the shield. 22