Modelization of the MiniCaLMa neutron monitor based on Geant4 and Garfield++

This paper describes the simulation of a portable neutron monitor suited for cosmic ray observation by detecting secondary particles, mainly neutrons, produced in the interaction of cosmic rays and solar energetic particles with the atmosphere. These instruments are known as mini neutron monitors and we focus on one of these detectors called MiniCaLMa from mini Castilla-La Mancha Neutron Monitor which is based on BF 3 for neutron detection. The model was developed using Geant4 to characterize the detector response to neutron beams and Garfield++ to simulate the ion/electron pair avalanches produced by these interactions. Incremental tests have validated the accuracy of the Geant4 model with calibrated measurements from standard NM64 neutron monitors. In addition, the raw pulses generated by the combined Geant4 and Garfield++ simulations show a qualitative alignment with the experimentally measured pulses in the detector. The simulations successfully reproduced the proportional region providing accurate pulse height spectra.