Characterisation of a medium-size-area high-rate multi-layer boron-coated GEM detector for thermal neutrons

During the last 10 years, the 3He crisis has brought to the development of new thermal neutron detection technologies and one of them is based on gas electron multiplier (GEM) principle. To detect neutrons, standard triple GEM detectors are usually coupled with a suitable converter, such as a 10B4C, where neutrons are converted via the nuclear reaction 10B(n,α)7Li. The number of converted neutrons can be enhanced by increasing the amount of boron present in the detector. A recent work has shown the possibility to cover the GEM foils on both sides with a double layer of 10B4C, and the device has been realised using 3 small-area GEM foils (3x3 cm2) coupled with the TimePix electronic readout. A new triple GEM coupled with 3 boron-GEM (BGEM) foils with a larger active area of 10×10cm2 has now been produced and characterised. The new detector is equipped with a 16×16 padded anode and with the GEMINI ASIC, a custom chip for GEM detectors. The device has been characterised with a thermal neutron beam provided at the Triga MARK II reactor in Pavia, to determine the working point, the detection efficiency, the counting rate and the imaging capability, showing similar performances to the previous smaller detector. In addition, the absolute detection efficiency respect to a reference 3He detector has been estimated.