New Neutron Beam Monitor Based on GEM

The high-intensity neutron total diffractometer (NOVA) constructed in BL21 of MLF [1] in J-PARC is one of the world’s most intense diffractometers. Since NOVA can observe structural changes in a very short time, it is a very powerful system for in-situ measurements. Because a time-slice measurement is usually performed in in-situ measurements, NOVA has to monitor the amount of incident neutrons with high accuracy. Therefore, an incident neutron beam monitor with the ability to monitor high counts is one of the key components of NOVA. We had already developed a two-dimensional neutron detector with a Gas Electron Multiplier (GEM) [2] as the incident neutron beam monitor of NOVA [3]. The GEM-based detector is a good neutron detector, but its electronics is obsolete and it is becoming more difficult to offer it as a new purchase. To overcome this problem, we developed a new neutron beam monitor (nGEM), which is an upgraded system that follows the basic design concept of the GEM-based detector. The nGEM is a gas-flow radiation detector that can measure charged particles from a n( 10 B, ) 7 Li nuclear reaction. The nGEM has a compact body of dimensions 524 mm × 254 mm × 50 mm. An Application Specific Integrated Circuit (ASIC) for pulse shaping and a Field Programmable Gate Array (FPGA) for online processing are also installed in the onboard electronics of the nGEM, which is able to transfer data directly to a PC via a network. The thermal neutron efficiency of the nGEM depends on the thickness of an ■■■ JPS Conf. Proc. , 036019 (2015)