Physics of auroral phenomena : proceedings of the 33rd Annual seminar, Apatity, 02 - 05 March, 2010 / [ed.: A.G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 206 с. : ил.

*P hysics o f Auroral P henom ena’’, Proc. XXXIII A n nu al Seminar, A patity, pp. 83 - 86, 2011 Polar © Kola Science Centre, Russian Academy of Science, 2011 GeoPhysical Institute MODELLING OF HADRON INTERACTIONS IN THE NEUTRON MONITOR E.A. Maurchev, B.B. Gvozdevskij, J.V. Balabin, E.V. Vashenjuk (Polar Geophysical Institute KSCRAS, 26a, Academgorodok Str., Apatity, 184209, Russia; E-mail: maurchev@pgai.ru ) Abstract. We have carried out two modelling experiments with a software package GEANT4, allowing investigating the neutron monitor (NM) response function to various kinds of radiation. In the first experiment the system of layers (the polythene-lead-polythene) simulating the parts o f a neutron monitor was irradiated with particle beams with random incident direction. As a result of calculations spectra of secondary neutrons which have reached the detector have been obtained. In the second experiment the whole neutron monitor was simulated, with geometry as much as possible approached to a reality. The particle flux simulating the basic components o f secondary cosmic radiation at the ground surface fell on the top surface of the instrument. For each particle the basic processes o f its interaction inside the neutron monitor were traced: 1 ) interaction with lead resulting to birth o f secondary neutrons, 2 ) moderation of them in polythene and 3) interaction with boron (10) nuclei which are a part of gas BF3, filling the neutron counter tube CNM-15. Responses and the relative contribution to the neutron monitor count rate of all kinds of secondary cosmic rays are calculated. In this work calculation results of the neutron response function are presented. Also the spectra of secondary neutrons obtained at modeling in the polythene-lead-polythene system, simulating the NM structure are presented. Introduction The neutron monitor section (NM, fig. 1, b) consists of six proportional counter tubes filled by the l 0 BF 3 gas. These counters are surrounded by a cylindrical polyethylene moderator (thickness of 2.5 cm). This inner moderator is installed inside of a great lead volume, so-called lead generator. Finally, the outer walls o f the NM again consist of polyethylene (7.5 cm thick) that forms the so-called reflector, because of which low-energy neutrons are scattered back into the NM from within or into space when they are going outside. In this work a series of modeling experiments aimed to investigate physics of interactions of cosmic ray particles in the neutron monitor with a software package GEANT4 were carried out. In the first experiment the system of layers polythene-lead-polythene was simulated with the purpose to improve understanding of physics of particle interaction in the matter surrounding the detector. The system was irradiated with beams of monoenergetic particles (n, p, n ) with energy 100 MeV, 300 MeV, 1 GeV and 10 GeV, as shown in fig. 1, a. lead producer / / detector у/ , polyethylene plates beam with RID* counter tube Fig. 1. A. The system used at the first modeling stage and simulating the construction of a neutron monitor. It consists of polyethylene plates, a lead plate (lead producer) and a detector of secondary neutrons. RID* is random incident directions. B. Real construction of the neutron monitor section 6-NM-64 used at the second modeling stage. It consists of six cylindrical proportional counter tubes (200 cm in length and 15 cm in diameter) surrounded by a cylindrical polyethylene moderators by thickness 2.5 cm. This construction is placed inside the lead producer (5 cm thick) and surrounded by the polyethylene reflector of 7.5 cm thickness. As a result multiplicity spectra o f secondary neutrons reaching a detector as well as their energy spectra in dependence on species and energies of primary particles were obtained. In the second experiment the whole neutron monitor was simulated for calculating the response function and tracking of secondary neutrons in the lead producer. The neutron monitor was irradiated with a particle flux incident perpendicularly to a surface with a random incident position, Fig. 2. As the results secondary neutrons typical tracings in a NM were obtained. Also the NM response function was calculated. 83