scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
The gamma-ray source input for the numerical simulation of the lightning neutron
generation
Malyshkin Yury
Lomonosov Moscow State University Skobeltsyn Institute of Nuclear Physics
There exist a number of experimental data favoring to the idea of correlation between the
thunderstorm discharge activity and growth of the neutron count rate in on-ground as well as
space detectors [1,2]. Furthermore, registered are the flashes of the gamma-ray photons in the
atmosphere (TGFs) also associating with thunderstorm discharges [3]. These are usually
accounted for by the bremsstrahlung radiation of the relativistic run-away electron avalanches
moving in the generated during thunderstorms electromagnetic fields. According to the theory
first proposed by Babich [4], in interaction of the TGF photons with the atmospheric nuclei
the neutrons are born. The question of possibility to detect such neutrons at orbital altitudes is
still disputed and various authors get opposite results (see [5,6] and references therein).
Though there appeared a lot of works devoted to these phenomena, the complete enough
account of the neutron source is lacking. This is, mostly, due to the fact, that for simulation of
the neutron source formation extremely simplified models of gamma-ray source are usually
used. However the spatial shape of the source (first of all its vertical size) can play rather
crucial role for the formation of neutrons and, possibly, for the total neutron flux at low
satellite orbits.
In the present study, we give corresponding analysis of the characteristics of bremsstrahlung
photons, generated by relativistic run-away electron avalanche. Using the Monte-Calro
numerical simulation package Geant4 we perform modeling of neutron generation process
owing to photonuclear reactions that take place during the thunderstorm discharges in the
atmosphere. At that, we take into account the most important features of the energetic and
spatial distributions of the gamma-ray photons, as well as atmospheric conditions. It is, in
particular, shown that the neutrons source can span up to several tens of kilometers, that leads
to some re-estimation of the neutron flux at low orbits.
References:
1. A.N.Shyam, et al.,(1999), Observation of neutron bursts associated with atmospheric lightning discharge,
J.Geophys.Res. v.104. p.6867–6869.
2. L.S.Bratolubova-Tsulukidze, et al.,(2004), Thunderstorms as the probable reason of high background neutron
fluxes at L < 1.2, Adv.Sp.Res 34. p.1815-1818.
3. D. M.Smith, et al.,(2005), Terrestrial gamma-ray flashes observed up to 20 MeV, Science, 307, p.1085–1088.
4. L.P.Babich, (2006), Generation of neutrons in giant upward atmospheric discharges, JETP Lett., 84, p.285–
288.
5. A.V.Grigoriev, O.R.Grigoryan, A.Drozdov, Yu.M.Malyshkin, Yu.V.Popov, E.A.Mareev, D.Iudin (in press),
Thunderstorm neutrons in near space: analyses and numerical simulation, J.Geophys.Res.
6. B.E.Carlson et al.,(in press), Neutron production in terrestrial gamma-ray flashes, J.Geophys.Res.
STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010