Preliminary FLUKA simulations of the Changvan Neutron Monitor

A neutron monitor (NM) is a ground- (or sea-) based detector of the flux of cosmic ray particles in space. The high-energy cosmic rays in the GeV primary range interact in the upper atmosphere, producing a cascade of subatomic particles, some of which reach Earth’s surface. A neutron monitor is mostly sensitive to the neutron component of the atmospheric cascade. The standard-design neutron monitor (NM64) contains lead, the nuclei of which fragment when struck by a high-energy particle. Some of the fragments are neutrons which are moderated and trapped by polyethylene acting as a reflector and moderator. These neutrons can then be detected by induced nuclear fission of 10B in a 10BF3 gas proportional counter. The Changvan neutron monitor is a portable neutron monitor assembled in Thailand and housed in a standard insulated shipping container to conduct long-term research in polar regions. There are three proportional counters in the Changvan, but the central counter lacks the lead producer. Since the detector has a non-standard semi-leaded design, we examine the detection efficiency of the Changvan for neutrons and other atmospheric secondary particles. We are also developing an electronic board and a highly sensitive control module to reduce dead time to a minimum, for monitoring neutrons in the GeV energy range. Simulation results accounting for the dead time will also be reported.