Three-dimensional tracking multi-segmented proportional gas counter for β-decay spectroscopy of unstable nuclei

We report on the performance of a recently developed high-efficiency, low-background, three-dimensional tracking multi-segmented proportional gas counter (3DT-MSPGC), intended for β -decay spectroscopy of neutron-rich nuclei in the vicinity of neutron magic number N =126 at the KEK Isotope Separation System (KISS) facility. The 3DT-MSPGC uses two concentric cylindrical layers of proportional gas counters (16 per layer, 32 in total) featuring resistive anode wires (3 k Ω /cm). By independently measuring the charge deposition from both ends of each counter, we constrain β particle trajectories and determine where they intersect with the central axis of the 3DT-MSPGC. New compact charge-sensitive pre-amplifier modules, along with shaping amplifier and fast-timing amplifier modules, were developed to deduce the hit position by precisely measuring the charge deposition and timing. We have studied the performance of the 3DT-MSPGC in on- and off-line experiments. A longitudinal position resolution of ≤ 3.5 mm (FWHM) was achieved for each counter. The determination of the event trajectories allowed for suppression of background events, resulting in the background-event rate reaching 0.020(3) count-per-second (cps) while still maintaining a high-detection efficiency. This reduction of background is shown to improve the signal-to-noise ratio in determination of the half-life of 196Ir by a factor of 2.3(6), resulting in a significant improvement in achievable precision.