Response of "Total Absorption" Spectrometers to Gamma Rays

A single crystal of sodium iodide 9-1/4 inches in diameter and 9 inches high with the top bevelled at 450 was recently obtained from Harshaw Chemical Company. A half-inch hole was drilled in the bevelled end to the center of the crystal. Three 5-inch diameter Dumont 6364's were optically connected directly to the flat end of the crystal. Sources were placed inside the crystal and γ spectra obtained, taking advantage of full geometry. A 4-3/4 inches diameter sodium iodide crystal 5-1/2 inches high with the top bevelled at 45° has a 1/4 inch hole drilled to the center. The crystal is optically connected to a Dumont 6364. The crystal is placed inside a 28-inch tank of liquid scintillator which uses four Dumont 6364's to detect pulses in the liquid. Samples are placed inside the crystal and the pulses from the crystal and liquid scintillator are placed in anticoincidence to reduce the Compton portion of the γ spectra. Typical spectra with these counters are shown along with ae comparison of data taken with these and smaller crystals.