Development of high-counting-rate measurement system for 3He position sensitive detector

We developed a high-counting-rate PSD system whose maximum counting rate is about four times higher than conventional PSD systems. By considering the RMS noise characteristics of the PSD, the shaping time was reduced to 0.1 μs, one fourth the time of conventional systems. In a PSD system, the trailing edge of the shaped pulse overshoots or undershoots depending on the neutron incident position, resulting in degradation of the position resolution at higher counting rates. The circuit constants were therefore optimized to keep the trailing edge constant. Moreover, the baseline fluctuation due to the ion current was eliminated by data processing. We evaluated the performance using PSDs of 6 to 25.4 mm diameter whose rise time was shortened with additive gas. Position resolution of 3.5 mm FWHM was obtained using a PSD with 12.7 mm diameter and 60 cm effective length at the value 1850V and 0.1 μs shaping time. For PSDs with diameters of 12.7 mm or less, better position resolution was obtained with 0.1 μs shaping time, and for PSDs with diameters exceeding 12.7 mm, better position resolution was obtained when the shaping time was larger than 0.1 μs. For a 0.1 μs shaping time, the position resolution obtained at 100 kcps was the same as that obtained at a low counting rate.