Numerical analysis of 2010 high-mountain (Tien-Shan) experiment on observations of thunderstorm-related low-energy neutron emissions

Abstract

The high-mountain experiment in a thunderstorm atmosphere, in which "extraordinary high flux of low-energy neutrons" was detected, is analyzed. Due to the lack of data on the radiation source, we do not analyze directly measured absolute count rates. Instead, we address the experimental configuration, namely, simultaneous measurements by shielded and unshielded helium counters, which allow a comparison of relative count rates and, thus, verifying the species of the detected radiation. Results of Monte Carlo simulations of neutron transport executed without aprioristic assumptions, using only data on the experimental configuration, have raised strong doubts as to whether the detected increases of the count rates can be attributed to neutrons. Results of simulations allowing for the neutron transport in atmosphere from distant (100-500 m) photoneutron source with spectrum in the range 0-20.1 MeV produced by relativistic runaway electron avalanche bremsstrahlung demonstrate that ratios R of the count rates of shielded and unshielded counters below 1 keV are manyfold higher than the ratios Rexp ≈ 0.34-1.06 of the measured count rates. In the total range 0-20.1 MeV, the R magnitudes vary from 0.14 to 0.84 depending on the distance to the neutron source. Results of simulations of γ rays transport executed without aprioristic assumptions demonstrate that, most likely, hard γ rays with energies εγ > 1 MeV were detected. We note that in thunderstorm environment, a selection is required of neutrons and γ rays, for which the time-of-flight technique is the most adequate. Key Points The experiment of Gurevich et al. (2012) is analyzed Monte Carlo simulations of neutron transport are performed Results of simulations demonstrate that gamma rays were detected © 2013. American Geophysical Union. All Rights Reserved.