Solar neutron transport in the Earth's atmosphere

Abstract

The neutron flux per unit energy induced in the earth's atmosphere by solar neutrons has been calculated as a function of atmospheric depth for depths of less than 300 g/cm² (∼30,000 ft). The calculated flux is compared with estimates of the cosmic‐ray neutron flux per unit energy, and it is found that for many flares the solar neutron flux per unit energy is sufficiently above the cosmic‐ray neutron flux per unit energy to produce a measurable effect at both balloon and aircraft altitudes.

A search for solar neutrons during solar flares

“…Let the total solar neutron count rate be N= N a + ND, where the subscript A refers to the contribution from atmospheric leakage and D to the contribution from solar neutrons directly incident on the detector. The calculations of Alsmiller and Boughner (1968) for the differential neutron flux produced at various depths in the atmosphere by solar flare neutrons can be used to estimate the resulting neutron leakage flux. The resulting neutron flux per unit energy versus energy at different atmospheric depths has the same spectral shape, in the neutron energy range 0.5-20 MeV, as the neutron energy spectrum calculated by Hess et al 0961) for cosmic-ray neutron production.…”

Upper limit to the 1?20 MeV solar neutron flux

“…In fact, no lower limits have been assigned in the 100-300 MeV energy interval than the early ones deduced by Webber and Ormes (1967). Although the calculations of Alsmiller and Boughner (1968) suggest that efficiency used by Webber and Ormes for the production of secondary protons by solar neutrons in the first few gm cm-z of the atmosphere might have been 50% too large, the value deduced for the solar neutron flux is still close to these new lower limits because the count rate limits set were very conservative. In the 2-20 MeV the OGO-6 solar neutron results set an order of magnitude lower upper limit than the measurements of Forrest and Chupp (1969) and Cortellessa et al (1971) in the overlapping energy range.…”

“…Let the total solar neutron count rate be N = N a + No, where the subscript A refers to the contribution from atmospheric leakage and D to the contribution from solar neutrons directly incident on the detector. The calculations of Alsmiller and Boughner (1968) for the differential neutron flux (neutrons cm -2 s -1 MeV -~) produced at various depths in the atmosphere by solar flare neutrons can be used to estimate the resulting neutron leakage flux. Then, the corresponding solar neutron fluxes (see Equation (2)) in the energy interval covered by the OGO-6 detector are: FD=ND/g D and FA=NA/2gA, since C=2 for a flux isotropic over a hemisphere.…”

A search for neutrons of solar origin using balloon borne detectors 1967?69

“…The limit (f) given by Webber and Ormes (1967) was obtained by observing secondary protons in the energy range 60-320 MeV at 12 gm cm -z residual atmosphere with a rotating detector telescope oriented at a zenith angle of 50 ~ and comparing the intensities when the detector was pointing towards and at 90 ~ away from the Sun. Forrest and Chupp (1969) have pointed out that the conversion efficiency of the overlying atmosphere for solar neutrons in the above energy range as deduced by Webber and Ormes is almost an order of magnitude higher than that indicated by the Monte Carlo calculations of Alsmiller and Boughner (1968). When extrapolating the atmospheric conversion efficiency from 320 MeV to 60 MeV Webber and Ormes assumed that the efficiency decreased as E ~'5, and we would like to suggest that the discrepancy between the Monte Carlo calculations and the extrapolated efficiency may be partly accounted for by a more rapid decrease in efficiency below 320 MeV than was assumed.…”