Thunderstorm neutrons in near space: Analyses and numerical simulation

Abstract

In this paper we perform a theoretical analysis of the direct passage of neutrons in the atmosphere from an altitude of about 5 km up to several hundred kilometers. We consider that these neutrons are generated during thunderstorms in what favor there is some experimental evidence. Two main mechanisms of the neutrons generation in thunderstorms appeared in the literature: the nuclear synthesis directly in the lightning channel and the photonuclear synthesis owing to production of gamma‐rays by the runaway electrons. Both of them are discussed in the present work. For the qualitative analysis we considered the process of neutrons propagation in the atmosphere as consisting of three stages: initial neutron deceleration to thermal energies, then diffusion, and further free propagation. Absorption of neutrons was neglected. Also, in modeling the atmospheric matter only nitrogen and oxygen were considered as the main atmospheric components. With these conditions and taking into account the predicted parameters of the neutron generation source, it is shown that the estimated flux well corresponds to the known experimental results. On this basis the preferred mechanism of the neutron generation is indicated. For a more rigorous picture of the neutrons propagation, capable for description of the slowing down, thermalization, and diffusion processes, one has to perform a numerical calculation and for this we propose a computer simulation scheme based on the cellular automation method. The corresponding plain analysis of the neutrons passage confirms the estimation mentioned above. The proposed scheme can be used for modeling the real neutron source. On the basis of our results we discuss some characteristic features of the observed neutron fluxes. The obtained results are to be tested by the “Radioskaf” experiment based on the scientific device called “RAZREZ.” One of the experiment objectives is detection of neutrons with different energies at altitudes of 200–400 km aiming to reveal the nature and characteristics of the neutron radiation source.