Studies of neutron detection and backgrounds with the DRIFT-IIa dark matter detector

摘要

Data from the DRIFT-IIa directional dark matter experiment are presented, collected during a near continuous 6 month running period. A detailed calibration analysis comparing data from gamma-ray, X-ray and neutron sources to a GEANT4 Monte Carlo simulations reveals an efficiency for detection of neutron induced recoils of 94 +/- 2(stat.) +/- 5(sys.)%. Software-based cuts, designed to remove non-nuclear recoil events, are shown to reject (CO)-C-60 gamma-rays with a rejection factor of better than 8 x 10(-6) for all energies above threshold. An unexpected event population has been discovered and is shown here to be due to the alpha-decay of Rn-222 daughter nuclei that have attached to the central cathode. A limit on the flux of neutrons (< 4 neutrons recoils day(-1)) in the Boulby Underground Laboratory is derived from analysis of unshielded and shielded data. (c) 2007 Elsevier B.V. All rights reserved.