Development of a minicomputer system for on-line processing of gamma--gamma coincidence events and measurements of E2/M1 mixing ratios in /sup 110/Cd and /sup 134/Ba

A megachannel pulse-height analysis system using a 32,000-word PDP-8/E minicomputer and two moving-head disk memories was developed. The system has a storage capacity of 2/sup 18/ events at any of 2/sup 20/ data locations, is capable of processing 1,040 events/s, and provides on-line sorting and disk storage. An X- or Y- pulse-height spectrum in coincidence with one to four arithmetically combined pulse-height windows can be assembled in core for scope display and spectral analysis within 2 to 20 seconds. The software for the system was written extensively in machine language. Excellent energy and timing resolution were achieved. An energy resolution of 2.3 keV fwhm and a timing resolution of 8.5 ns fwhm were obtained for /sup 60/Co at a singles rate of 10,000 counts/s. The prompt timing peak remained Gaussian down to the fwtm by gating the TAC with SCAs which discriminated against low-energy events. The coincidence electronics also allowed on-line subtraction of accidental coincidence events. Alignment of the detectors and tests of the system's performance were made by measuring solid-angle correction factors for the Ge(Li) detectors through the correlation measurements of the 0/sup +/--2/sup +/--0/sup +/ cascade in /sup 106/Pd, and by measuring the angular spread of positron annihilation radiation coincidences. These experimental results were in excellent agreement with theoretical solid-angle correction factors calculated. Directional correlation data were obtained for gamma-ray cascades in /sup 134/Ba and /sup 110/Cd. Analyses of these data gave E2/M1 mixing ratios which are in excellent agreement with results obtained by other investigators. The improved resolution and data processing capabilities of this system gave new results for the 563-keV transition in /sup 134/Ba and the 1505-keV transition in /sup 110/Cd. E2/M1 mixing ratios of 13.3/sup +2.3/sub -1.8/ for the 563-keV transition and -1.24 +- 0.20 for the 1505-keV transition were measured