Computer-coupled Ge(Li) spectroscopy in neutron activation analysis of semiconductor silicon

The spectrometer system developed in this work consists of a Ge(Li) detector and a 4096-channel multichannel analyzer interfaced directly to a computer with 16,384 24-bit words. The restrictions imposed by a medium-sized core have been circumvented by performing the data reduction in successive steps which are called from a disk file while the data remain in core. Since the analyzer memory is not used to store data during reduction, new data can be acquired while data reduction is in progress. The disk file includes routines for energy calibration, efficiency calibration for each of the geometries used in counting, smoothing, and peak location and integration. The output options include linear or semilogarithmic plots of the spectra. Calibration in the energy region 40-1600 keV is done with a mixed source 57Co, 137Cs, and 60Co. Since the samples are routinely irradiated under reproducible conditions in the same reactor, the flux can be derived from a single flux value obtained from a gold and cobalt monitor. Analysis of standard mixtures indicates an accuracy ranging from ±4.9 to ±7.5%, depending on the counting statistics. Silicon analyses using this system are compared to the more classical NaI(Tl) system. The increased Ge(Li) detector resolution makes possible analyses of silicon samples which could not be performed on a NaI(Tl) detector.