A modular large-area lithium foil multi-wire proportional counter neutron detector

摘要

Several Li foil multi-wire proportional counters were constructed with five layers of 75 gm thick Li-6 foils spaced 1.63 cm apart. Each detector had 1250 cm(2) of active area and was backfilled with 1.0 atm of P-10 gas. Two of these detectors were positioned back-to-front with 5.0 cm of high-density polyethylene (HDPE) positioned between the two detectors and on the front and back. Additional 2.54 cm thick HDPE sheets were added to the remaining sides. The detectors were operated with a single electronics unit and were delivered to a test facility where multiple neutron and gamma-ray sensitivity experiments were completed. First, a Cf-252 neutron source was positioned at various distances from the front of the detector and the absolute detection efficiency (cps ng(-1)) was recorded at each distance. Second, a transient test was completed by moving the neutron source in front of the detector at a constant rate while recording the change in count rate (cps). Third, the lateral sensitivity and symmetry of the detection system was investigated by positioning a Cf-252 source up to 5.0 m away from the centerline of the arrayed detectors in 1.0 m increments in both outward directions. The angular response was investigated by positioning the Cf-252 source 2.0 m from the center of the device and recording the count rate at each stationary position in 15 degrees increments from 0 degrees to 360 degrees. The count rate varied 15% from minimum to maximum during the angular response test. Additionally, the arrayed system was modeled in MCNP6 and had an intrinsic neutron detection efficiency of 12.6% for a bare Cf-252 source, less than the experimentally determined efficiency of 13.9 +/- 0.03%, as expected. The gamma-ray sensitivity of the detection system was also investigated and pulse-height spectra were collected and plotted against a neutron response spectrum for comparison. (C) 2015 Elsevier Ltd. All rights reserved.