Monte Carlo Simulation of BP28 and LND Boron Trifluoride Tube Responses in Neutron Monitors at PSNM

Neutron monitors are essential instruments for studying cosmic rays, requiring accurate response modeling for interpreting flux variations. A new boron trifluoride (BF$_3$) proportional counter from LND Inc. matches the geometry, gas volume, and pressure of the standard NM64 BP28 counter but differs in anode and cathode thickness. At the Princess Sirindhorn Neutron Monitor (PSNM) in Chiang Mai, Thailand, an LND tube temporarily replaced one of three bare BP28 tubes between September 2022 and October 2023. This substitution enabled a direct comparison of their responses. Using Monte Carlo simulations with monthly solar modulation parameters from Usoskin et al.\ (2017), we modeled secondary particle interactions within these detectors. Simulated responses were benchmarked against actual count rates, confirming that the LND tube’s sensitivity was consistently about 0.93–0.95 relative to the BP28, aligning closely with laboratory calibrations. These findings validate the LND tube as a viable alternative for neutron monitor networks