Atmospheric effect on cosmic ray produced neutron: mini neutron monitor experimental results

Primary cosmic rays (PCRs) interact with atmospheric nuclei producing a myriad of secondary particles known as secondary cosmic rays (SCRs) that can be measured with ground-based detectors such as neutron monitors. Neutrons, protons, pions or muons are some of the particle species of these SCRs. Their flux is related to the kinetic energy of the PCRs and shows a strong dependence on the pressure level at the observation site reflecting their dependence on the amount of matter they have to pass through the atmosphere. In addition, the air column above the observation point evolves continuously introducing temporal changes in the SCR flux due to atmospheric conditions. This atmospheric effect is taken into account by the β factor, which is the exponent of the exponential relationship between the atmospheric pressure and the SCR count rate, being mostly neutrons in the case of neutron monitors. On the other hand, pressure shows an inverse dependence with height above sea level and this should be reflected in the neutron monitor count rate as it is measured at different altitude levels. Altitude surveys with a mobile neutron monitor are essential for understanding how the atmosphere affects SCR production and for cross-checking models describing the interaction between cosmic rays and atmospheric atoms. From October 2023 to September 2024, one such survey was carried out with a mini neutron monitor on the island of Tenerife. Four sites were visited at the altitudes of 20, 868, 2390 and 3355 meters above sea level, respectively. A control point to monitor solar activity during altitude sounding has been established at the 2390 m site where a standard 3NM64 neutron monitor has been operating since early 2023 at the Izaña Atmospheric Observatory. The results of the experiment are presented and discussed and the dependence of the β factor on the multiplicity in the mini neutron monitor is noted, suggesting an energy dependence of the β factor.