Advancements in microstructured semiconductor neutron detector (MSND)-based instruments

Abstract

Microstructured semiconductor neutron detectors (MSNDs) represent a compact, low-cost, high-efficiency means of solid-state thermal neutron detection. Trenches are etched into a 1-cm2 or 4-cm2 active area pn-junction diode and backfilled with 6LiF neutron converting material. Charged-particle reaction products produced from neutron capture within the conversion material can be measured to indicate the presence of neutrons. MSNDs can be arranged into larger instruments due to their small size, high-efficiency, and low power consumption. A small, inexpensive electronics package named the ‘Domino’ was developed to facilitate the deployment of the MSND™ technology. The Domino is a complete electronics package that supports a single MSND™ with all necessary signal processing electronics. The Domino electronics were tiled together to form large-area arrays and portable detector arrays. Both were characterized with a small 252Cf source. A hand-held portable ‘Briefcase’ detector with 84 Dominoes™, forming a 30 cm × 38 cm array, weighed 21 lbs. A vehicle-portable ‘Panel Array’ detector with 480 Dominoes formed a 1 m × 1 m. For a bare 252Cf source, the ‘Briefcase’ detector and the ‘Panel Array’ detector yielded 0.27 ± 0.01 cps ng−1 (at 2 m) and 0.45 ± 0.01 cps ng−1 (at 5 m), respectively. Modified Domino packages (with upgraded MSNDs) were arranged into a 2-in. diameter, 6-in. long cylindrical form factor (HeRep Mk II) for direct 3He replacement, matching the efficiency of a 4-atm 3He with similar dimensions. A third generation helium replacement (HeRep Mk III) was constructed to replace more compact 3He form factors, with a 0.75-in. diameter and 4.5-in. length. Populated with dual-sided MSNDs, this detector yielded 0.293 ± 0.003 cps ng−1 for bare 252Cf at 0.2 m.