184 FOOTE for data accumulation. Each counting period was followed by data read- out on punched paper tape and initiation of the subsequent counting period. All data were tape-to-card converted and supplied to a computer for réduction. The field-instrumentation enclosure with its detector pod is shown in Fig. 1. An example of the change in time of the Fig. 1—-Field instrumentation for total-absorption gamma-ray spectrometer. field gamma-ray energy spectral shape caused from decay of surface nuclear fallout is given in Fig, 2. Proper and adequate methods of data reduction mustthen beutilized to determine what radionuclides provide the gammaradiation of which the field spectrum is composed. The precise energy spectral calibration standard of each radionuclide composing the field gamma‘ray spectrum must be determined. The optimum computer method for the determination of the amounts of each radionuclide must be resolved on the basis of the computer time requirement and results. Energy calibration of all spectral data is required. The radionuclides that create the most intense gamma-ray energy lines can initially be lo- cated. The selection of two energy lines such as the 2.615-Mev line from 787] and a line of lesser energy, preferably of low energy, allows energy calibration to a high degree of accuracy and consistency.! There are many ways of locating the photopeak energy positions, Texas In- struments’ method of locating is indicated in Fig. 3, where the sides of a near-Gaussian-shaped curve are matched by two straight lines; the 16h