Monte Carlo simulations for high-rate fast neutron flux measurements made at the RAON neutron science facility by using MICROMEGAS

Abstract

RAON is a Korean heavy-ion accelerator complex that is planned to be built by 2021. Deuterons (53 MeV) and protons (88 MeV) accelerated by using a low-energy driver linac (SCL1) are delivered to the neutron production target in the Neutron Science Facility (NSF) to produce high-energy neutrons in the interval from 1 to 88 MeV with high fluxes of the order of 10(12) n/cm(2)-sec. The repetition rate of the neutron beam ranges from 1 kHz to 1 MHz, and the maximum beam current is 12 mu A at 1 MHz. The beam width is 1 2 ns. The high-energy and high-rate fast neutrons are used to estimate accurate neutron-induced cross sections for various nuclides at the NSF. A MICROMEGAS (MICRO Mesh Gaseous Structure), which is a gaseous detector initially developed for tracking in high-rate, high-energy physics experiments, is tentatively being considered as a neutron beam monitor. It can be used to measure both the energy distribution and the flux of the neutron beam. In this study, a MICROMEGAS detector for installation at the NSF was designed and investigated. Li-6, B-10, U-235 and U-238 targets are being considered as neutron/charged particle converters. For the low-energy region, Li-6(n,(alpha))t and B-10(n,(alpha))Li-7 are used in the energy range from thermal to 1 MeV. U-235(n,f) and U-238(n,f) reactions are used for high-energy region up to 90 MeV. All calculations are performed by using the GEANT4 toolkit.