Ṡtabilization of a gamma scintillation spectrometer against zero and gain drifts

Abstract

In this paper is described the theory, design, and performance of a device which corrects zero and gain drifts of any origin in a gamma-ray scintillation spectrometer consisting of NaI(Tl) crystal and multichannel pulse-height analyzer. This correction is automatic and continuous througout operation of the spectrometer. Stability of peak channel numbers to 0.1 percent or better seems attainable over indefinite periods of time without important penalties. Reference gamma rays, having low and high energies, respectively, and accompanied always by coincident beta rays which uniquely distinguish them from all other gamma rays, are emitted from a special source close to the detector. The spectrometer determines the channel number of these reference gamma rays as for other gamma rays, but does not store the counts in its memory. The stabilization device adjusts zero and gain, by means of feedback voltages applied to analyzer window threshold and photomultiplier dynode voltage, respectively, so as to hold the two reference peaks always in the preassigned channels. Thus the same reference spectrum is used for all experimental spectra (without, however, contributing appreciably to background), and the stabilization feedback loop encompasses the entire analogue portion of the spectrometer.