Development of a handheld thermal neutron detector (GAMBE) using stacked silicon sensors coated with 6LiF films

Abstract

Thermal neutron detectors, which are based on semiconductor material such as silicon coated with neutron reactive material like 6LiF have been discussed for many decades. The performance of the thermal neutron detector system, GAMBE (GAMma Blind neutron Efficient), which is based on two silicon sensors in a sandwich configuration is investigated. This detector is able to achieve a total and a coincidence detection efficiency of 4% and ~1% respectively. The thermal neutron detection efficiency of the detector is enhanced by using a stacked detector configuration and high-density polyethylene (HDPE) sheets, as neutron moderators and reflectors. The GAMBE detector is positioned inside a box of HDPE with a lead window in the direction of the neutron flux for neutron moderation and a reduction of the effect of gamma-rays on the detector. The experimental layout was modeled in MCNP4C to investigate the contribution of HDPE to the thermal neutron flux (n/s/cm2). In this research a stack of 4 silicon semiconductor sensors with (2.6 ± 0.6) and (2.9 ± 0.6) mg/cm2 thick 6LiF film in a configuration of two sandwiches is shown to achieve a total and a coincidence detection efficiency of 27% and 4% respectively. This represents a significant improvement compared to a single detector. The effect of these stacked detectors for the development of a handheld thermal neutron detector, using 4 coated Si detectors is shown to have a 22% efficiency. This information is used to deduce the optimised design of the handheld detector. The results based on Geant4 and MCNP simulations indicate that the total detection efficiency of this portable detector with a stack of 7 sandwich detectors will increase up to 52% by using an optimal thickness of 6LiF of 3.95 mg/cm2 (≈17 μm).