Abstract
Abstract. Ground-based measurements of neutrons from secondary cosmic rays are affected by environmental parameters, particularly hydrogen content in soil. To investigate the impact of these parameters, in particular snow cover, Geant4 Monte Carlo simulations were carried out. In a previous study the model used for the Geant4 Monte Carlo simulations was already validated by measurements performed with an extended-range Bonner sphere spectrometer (ERBSS) at Zugspitze, Germany, and at Jungfraujoch, Switzerland. In the present study a sensitivity analysis including different environmental parameters (i.e. slope of mountain, snow height, and soil moisture) and their influence on the flux of neutrons from secondary cosmic rays was performed with Geant4. The results are compared with ERBSS measurements performed in 2018 at the Environmental Research Station Schneefernerhaus located at the Zugspitze, Germany. It is shown that the slope of the Zugspitze mountain reduces the neutron flux from secondary cosmic rays between about 25 % and 50 % as compared to a horizontal surface, depending on neutron energy and snow cover. An increasing height of snow cover, simulated as snow water equivalent (SWE), reduces the total neutron flux exponentially down to a factor of about 2.5 as compared to soil without any snow cover, with a saturation for snow heights greater than 10 to 15 cm SWE, depending on neutron energy. Based on count rates measured with the individual spheres of the ERBSS, SWE values were deduced for the whole year 2018. Specifically, mean SWE values deduced for the winter months (January to March) are between 6.7 and 10.1 cm or more, while those for the summer months (July to September) are between 2.1 and 3.6 cm. Soil moisture of 5 % water mass fraction in limestone leads to a decrease of the total neutron flux by about 35 % compared to dry limestone. It is concluded that the measurement of neutrons from secondary cosmic radiation can be used to gain information on the height of snow cover and its seasonal changes, on soil moisture, and on local geometry such as mountain topography. Because the influence of such parameters on neutron flux from secondary cosmic rays depends on neutron energy, analysis of the whole neutron energy spectrum is beneficial.
Highlights
Neutrons from secondary cosmic rays (CRs) are always present at the Earth’s surface as a component of natural radiation background
The neutron flux spectra simulated in the previous paper for a slant angle of 45◦ (Brall et al, 2021) could be compared with those obtained in the present study using horizontal ground
The simulations described in the present paper were done for the UFS at an altitude of 2661.5 m a.s.l. on a limestone ground assuming a horizontal surface
Summary
Neutrons from secondary cosmic rays (CRs) are always present at the Earth’s surface as a component of natural radiation background. These neutrons are produced during cascade reactions in the Earth’s atmosphere by primary CRs (mainly protons and helium nuclei). The CR particles interact with the atoms of the air (basically oxygen and nitrogen atoms) and are continuously slowed down due to ionization They interact with the nuclei of these atoms, and new particles like protons, neutrons, and and K mesons are produced and characterized by a wide spectrum of energies extending up to several GeV. The transport of fast neutrons through soil is strongly influenced by the presence of hydrogen, which has the ability to rapidly moderate neutrons due to its large elastic scat-
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