Preprints
https://doi.org/10.5194/tc-2021-152
https://doi.org/10.5194/tc-2021-152

  15 Jun 2021

15 Jun 2021

Review status: a revised version of this preprint was accepted for the journal TC and is expected to appear here in due course.

Assessment of neutrons from secondary cosmic rays at mountain altitudes – Geant4 simulations of environmental parameters including soil moisture and snow cover

Thomas Brall1, Vladimir Mares1, Rolf Bütikofer2, and Werner Rühm1 Thomas Brall et al.
  • 1Helmholtz Zentrum München, Institute of Radiation Medicine, Ingolstädter Landstr. 1, 85764 Neuherberg, Germany
  • 2University of Bern, Space Research & Planetary Sciences, Sidlerstrasse 5, 3012 Bern, Switzerland

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, 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, soil moisture, and range of albedo neutrons) 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 cm 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. At a height of 1.5 m above ground, 86 % of the total albedo neutron fluence at the detector position are from a ground area with a radius of about 75 m. It is concluded that measurement of neutrons from secondary cosmic radiation can be used to gain information on height of snow cover and its seasonal changes, soil moisture, but also information on local geometry such as mountain topography. Because the influence of such parameters on neutron fluence from secondary cosmic rays depends on neutron energy, analysis of the whole neutron energy spectrum is beneficial.

Thomas Brall et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2021-152', Anonymous Referee #1, 23 Jun 2021
    • AC1: 'Reply on RC1', Thomas Brall, 08 Aug 2021
  • RC2: 'Comment on tc-2021-152', Anonymous Referee #2, 30 Jun 2021
    • AC2: 'Reply on RC2', Thomas Brall, 08 Aug 2021

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2021-152', Anonymous Referee #1, 23 Jun 2021
    • AC1: 'Reply on RC1', Thomas Brall, 08 Aug 2021
  • RC2: 'Comment on tc-2021-152', Anonymous Referee #2, 30 Jun 2021
    • AC2: 'Reply on RC2', Thomas Brall, 08 Aug 2021

Thomas Brall et al.

Thomas Brall et al.

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Short summary
Neutrons from secondary cosmic rays, measured at 2660 m a.s.l. at Zugspitze, Germany, are highly affected by the environment in particular by snow, soil moisture and mountain shielding. To quantify these effects, computer simulations were carried out, including a sensitive analyses on snow depth, soil moisture, and range of back scattered neutrons. This provides a possibility for snow depth estimation based on measured number of secondary neutrons. This method was applied at Zugspitze in 2018.