Monte Carlo simulation of the neutron monitor yield function

• Published in: Journal of geophysical research. Space physics 2016-08, Vol.121 (8), p.7435-7448
• Main Authors: Mangeard, P.‐S., Ruffolo, D., Sáiz, A., Madlee, S., Nutaro, T.
• Format: Article
• Language: English
• Subjects: Alpha particles; Alpha rays; Atmosphere; Atmospheres; atmospheric showers; Coefficients; Computer simulation; Cosmic rays; Counting; Data assimilation; Data base management systems; Data collection; Design analysis; Design engineering; Design standards; Detectors; Electronics; Estimates; Geomagnetic field; Geomagnetism; Geophysics; Incoherent scatter radar; Mathematical models; Monitors; Monte Carlo methods; Monte Carlo simulation; Navy; neutron monitors; Neutrons; Radar; Rigidity; Solar minimum; Tubes
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1002/2016JA022638

Neutron monitors (NMs) are ground‐based detectors that measure variations of the Galactic cosmic ray flux at GV range rigidities. Differences in configuration, electronics, surroundings, and location induce systematic effects on the calculation of the yield functions of NMs worldwide. Different estimates of NM yield functions can differ by a factor of 2 or more. In this work, we present new Monte Carlo simulations to calculate NM yield functions and perform an absolute (not relative) comparison with the count rate of the Princess Sirindhorn Neutron Monitor (PSNM) at Doi Inthanon, Thailand, both for the entire monitor and for individual counter tubes. We model the atmosphere using profiles from the Global Data Assimilation System database and the Naval Research Laboratory Mass Spectrometer, Incoherent Scatter Radar Extended model. Using FLUKA software and the detailed geometry of PSNM, we calculated the PSNM yield functions for protons and alpha particles. An agreement better than 9% was achieved between the PSNM observations and the simulated count rate during the solar minimum of December 2009. The systematic effect from the electronic dead time was studied as a function of primary cosmic ray rigidity at the top of the atmosphere up to 1 TV. We show that the effect is not negligible and can reach 35% at high rigidity for a dead time >1 ms. We analyzed the response function of each counter tube at PSNM using its actual dead time, and we provide normalization coefficients between count rates for various tube configurations in the standard NM64 design that are valid to within ∼1% for such stations worldwide. Key Points We calculated the neutron monitor (NM) yield function by Monte Carlo simulation of cosmic ray‐induced interactions in the atmosphere and NM The simulated count rate due to cosmic rays for an NM at Doi Inthanon, Thailand, matches observations to within 9% We calculated effects of the geomagnetic field and dead time and normalization coefficients for common NM64 detector configurations