The Characteristics of B4C Coated Scintillators

Abstract: The characteristics of Boron Carbide (B4C) coated polyvinyltoluene scintillators with a sputtered B4C coating ranging between 200 and 1000 nm have been studied using a photomultiplier - Lanthanum Bromide detector setup with a PuBe neutron source. The raw data from the detectors was analysed by imposing a detector coincidence condition. The coated scintillators have been compared with a commercial homogeneously doped B4C scintillator. Furthermore, a measurement of the homogeneity of the B4C coating has been performed using a proton beam at the Lund Ion Beam Analysis Facility (LIBAF) accelerator at the division of nuclear physics, at Lund university. Alpha - gamma coincidence measurements on the 1000 nm coated scintillator showed a discernible alpha signal in the 480 keV gamma region. The gamma-ray count rate for the coated scintillator was found to be 0.25 CPS compared to 16 CPS for the commercial scintillator at a time resolution of 3.7 ns and 7.9 ns respectively. The drastically lower count rate can be attributed several factors, though mainly due to the lower amount of Boron-10 in the B4C layer of the coated scintillator. The coincidence measurements showed that B4C coated scintillators are, under the conditions set up in the study, a feasible way of detecting moderated neutrons. The lower resolution of the coated scintillator can be attributed to the need for a highly amplified signal, which generated more electronic noise. The measurement time was also substantially longer. Due to the lower count rate the area of application of these scintillators would best suit a measurement where the count rate is not of principal importance. Boron-11 proton probing of the 200 and 600 nm coated scintillators showed that the counts followed a Poisson distribution with a discrepancy of 25 and 11%, respectively, this data was however not normalised for beam charge fluctuation.