TOTAL-ABSORPTION GAMMA-RAY SPECTROSCOPY 197 The replacement of the matrix-reduction method by the leastSquares method is being evaluated. The improvement by use of the least-Squares technique is insignificant if routine calculations are being made With known spectra, whereas the cost per spectrum is approximately four times greater than with the use of the matrix technique. If . unknown inputs are involved, the least-squares technique is Superior. ’ Investigations and comparisons are being made by Bruce Foster using techniques similar to those of Trombka.’ Current computer-reduction costs for the matrix technique are about $0.15 per spectrum. It is felt that field gamma-ray measurements offer the most rapid method for the determination of the presence, the type, and the amount of radioactive fallout. The equipment is compact and portable, permitting transportation by aircraft or other vehicle to any location. REFERENCES 1. R. S. Foote, Measurement of Radioactive Fall-Out by Field Total Absorption Gamma Ray Spectroscopy, Report No.1, AEC Contract AT(40-1)-3147, Texas Instruments, Inc., Sept. 30, 1963. 2. J. 1. Trombka, Least-Square Analysis of Gamma-Ray Pulse Height Spectra, Technical Report No. 32-373, Jet Propulsion Laboratory, California Institute of Technology, Dec. 15, 1962.