Monte Carlo Simulation Study on the Physical Process of the Boron-coated GEM Neutron Beam Monitor

Key words: 
• neutron beam monitor /
• GEM /
• boron convertor /
• Geant4

Abstract: The performance of a boron-coated GEM (Gas Electron Multiplier) neutron beam monitor is outstanding, with the counting rate up to 10 MHz, radiation resistance, flexible readout patterns, high resolution in position and time, which is considered as a good candidate for the next generation of neutron beam monitor. This new kind of neutron beam monitor mainly consists of boron convertor, GEM and two-dimensional readout electrode. In this paper, the Monte Carlo simulation on the physical process of the detector has been carried out by using Geant4 package, including the conversion efficiency of the boron layer influenced by the thickness and the neutron wavelength, the spectrum of emitted ions, and the energy deposition of the ions and the gamma in the different gas thickness of several gas volume ratio. Besides, the effect by the fast neutrons with GEM foils has also been calculated. The results show that the ions energy deposited in the drift region is almost independent of the gas volume ratio, the thickness 6 mm of the drift region is adequate for the full energy deposition and the boron thickness smaller than 0:1 m is the best choice for n/ separation. This work would be helpful for the detector design and provide an optimized option for the development of the boron-coated GEM neutron beam monitor.