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A γ-ray spectrometer has been constructed based on the use of a PDP-8/e computer. The system operates in the singles or coincidence pulse-height analysis mode from one, two or three analog-to-digital converters (ADC). Any one of the ADC outputs can be stored separately or any two can be stored simultaneously in the so called dual-singles storage mode. The interface also allows the storage of two- or three-parameter coincidence data the output of which is recorded event-by-event on industry compatible magnetic tape. Input to the computer is made via an external patch panel connection which allows total flexibility in the selection of data formating to magnetic tape. A simple circuit has been developed to allow the PDP-8/e to be held at memory cycle time TP4 so that the rather restrictive timing requirements of the processor can be easily met. The circuit often allows the saving of a complete memory cycle period (≈ 1.4 μ s) by delaying the processor at TP4 by only a few nanoseconds.

A three-parameter coincidence data collection system has been constructed based on the use of computer compatible magnetic tape. The system was designed for use at the thermal neutron capture gamma-ray facility at the Georgia Institute of Technology Research Reactor. Up to three 12 bit words can be used to describe the coincidence event. The first two words consist of the output from two analog-to-digital converters (ADC) e.g. two 2048 channel energy spectra. The third word consists of the output of a 256 channel ADC e.g. time spectrum, plus four “status registers”. The system is highly versatile and operates in the one-, two- or three-parameter mode. The interfacing logic is based on the use of commercially available circuit boards. Each function of the logic can be tested via commands from a PDP-8 series computer although the device is completely independent of the computer when operating in the data acquisition mode.

A new technique has been developed to determine precisely the fraction of all counting losses suffered in counting and pulse height analysis systems. Of particular significance is the applicability of this method to time-dependent counting rates. The method is based on a technique in which the rate of radiation incident upon the detector is sampled continually. Upon the detection of a preset number of counts, a pulser signal is injected into the preamplifier. At the end of the experiment, the total number of injected pulses is compared with the number of these pulses that are recorded in the multichannel analyzer or scaler. Since the pulser peak suffers the same fractional losses as the spectral components of the detected nuclear events, such a comparison provides an accurate representation of the counting losses due to all loss-producing effects. These include losses incurred in ADCs, computers, pileup rejectors, etc. Losses suffered due to pileup may not be negligible compared with those due to the ADC and memory of fast multichannel analyzers. The application of this technique to constant counting rates, and to varying counting rates encountered in charged-particle-induced reactions and in radioactive-decay studies are treated in detail.