An improved method of correlation counting using a bi-dimensional data acquisition system

A bi-dimensional data acquisition system has been developed in order to carry out correlation counting experiments. The data, comprising pulse height and input timing with a resolution order of 100 ns for all beta and gamma signals, are simultaneously recorded on a static random access memory (SRAM). The coincidence resolving time and the various gamma windows are selected by a computer analysis program, and the efficiency functions are obtained by the computer discrimination method. The method is particularly well applicable to activity determination in cases where radionuclides decay by cascade processes with relatively long-lived intermediate states. The fraction of the delayed events in the decay of 75Se has been studied by means of a pressurized proportional counter and NaI(Tl) detector system. The measurement time was 9000 s for each sample, sufficient not only to obtain the total electron capture detection efficiencies but also to find the efficiency variation curve for the fraction of the correlated event pairs detected in the proportional counter. These fractions have been determined by sequentially sorting the data in 2 × 105 intervals of 45 ms duration, at each discrimination level assigned to the pulse height spectrum in the proportional counter. The results are discussed and compared with previous results.