Reducing Pulse Height Spectral Distortion by Means of DC Restoration and Pile-Up Rejection

The problem of pulse height spectral distortion created by pile-up effects of randomly distributed events in nuclear spectrometry systems has become extremely important since the advent of the use of germanium detectors in gamma-ray spectrometry. The study of this problem is complicated by the fact that the pulse height response of the detector to incident gamma-rays contains a photopeak and a Compton continuum, which represents a broad spectrum of pulse heights. Analysis of spectrum distortion must involve the complicated separation of all possible combinations of the involved pulse heights and pulse period overlap. Indeed, almost all sources of signals which might be used for such a study as this are either non-random or have a broad distribution of pulse heights. There is one notable exception, which is the charged particle source and semiconductor detector combination, e.g., an alpha source and a surface barrier diode in vacuum; however, sources of sufficient strength to provide the high count rates necessary for definitive testing are difficult to handle and may present a personnel hazard. Presented here is a method of assembly, from standard laboratory equipment, of a monoenergetic, random time-interval, pulse generator with variable pulse height and count rate for the study of count rate spectral distortion in nuclear electronics. The necessary equipment consists of a noise source, a discriminator, a time-to-pulse-height converter (non-shaping type), and a section of coaxial cable for delay.