Controlling low-rate signal path microdischarge for an ultra-low-background proportional counter
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Controlling low-rate signal path microdischarge for an ultra-low-background proportional counter E. K. Mace • C. E. Aalseth • R. M. Bonicalzi A. R. Day • E. W. Hoppe • M. E. Keillor • A. W. Myers • C. T. Overman • A. Seifert
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Received: 16 July 2012 / Published online: 5 September 2012 Ó Akade´miai Kiado´, Budapest, Hungary 2012
Abstract Pacific Northwest National Laboratory (PNNL) has developed an ultra-low-background proportional counter (ULBPC) made of high purity copper. These detectors are part of an ultra-low-background counting system (ULBCS) in the newly constructed shallow underground laboratory at PNNL (at a depth of *30 m water-equivalent). To control backgrounds, the current preamplifier electronics are located outside the ULBCS shielding. Thus the signal from the detector travels through *1 m of cable and is potentially susceptible to high voltage microdischarge and other sources of electronic noise. Based on initial successful tests, commercial cables and connectors were used for this critical signal path. Subsequent testing across different batches of commercial cables and connectors, however, showed unwanted (but still low) rates of microdischarge noise. To control this noise source, two approaches were pursued: first, to carefully validate cables, connectors, and other commercial components in this critical signal path, making modifications where necessary; second, to develop a custom lownoise, low-background preamplifier that can be integrated with the ULBPC and thus remove most commercial components from the critical signal path. This integrated preamplifier approach is based on the Amptek A250 low-noise charge-integrating preamplifier module. The initial microdischarge signals observed are presented and characterized according to the suspected source. Each of the approaches for mitigation is described, and the results from both are
compared with each other and with the original performance seen with commercial cables and connectors. Keywords Ultra-low-background Microdischarge Proportional counter Low noise
Introduction Pacific Northwest National Laboratory (PNNL) has developed ultra-low-background proportional counters (ULBPC) made of high purity copper [1]. In ultra-low-background measurements, it is critical that the microdischarge or noise rate be extremely low. Sources of noise can come from microdischarge events in dielectrics in the electronics, cables, and connectors [2], from microphonics due to the motion of conductors [3], and from fluctuations in the high voltage supply. Each type of noise event has a characteristic pulse shape which can be excluded during the analysis using pulse shape discrimination (PSD). However, the fact remains that a noisy environment can significantly increase the amount of dead time for a detector as well as interfering with the low rate signal being measured in the detector. Therefore, it is imperative to identify sources of noise and eliminate them where possible from the critical signal path of an ultra-low-background detector.
Experimental E. K
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