Neutron measurements in space

Abstract

The experimental measurements of the neutron flux and energy spectrum in space since 1964 are reviewed and related to the theoretical predictions. A discussion of the neutron sources is presented. The difficulties associated with neutron measurements of both the atmospheric neutron leakage flux and solar neutrons are included. Particular emphasis is placed upon the neutron leakage flux and energy measurements at energies greater than about 1 MeV. The possibilities of CRAND as a source for the energetic trapped protons are discussed in light of recent measurements of the 10-100 MeV neutron flux. The current status of the solar neutron flux observations is also presented.The primary purposes of neutron measurements in space have been to determine the neutron leakage flux from the atmosphere of the Earth and the solar neutron flux. As a consequence of the inefficient methods for neutron detection and the difficulties of conducting the measurements in the presence of the galactic and solar cosmic-ray backgrounds, the experimental results are very conflicting. It is the purpose of this review to interpret and discuss recent neutron measurements. In order to understand these results the theoretical predictions of the neutron fluxes and energy spectra from possible neutron sources will be briefly presented. Since comparisons of the different neutron measurements depend critically upon the experimental techniques, we will briefly discuss neutron detection methods applicable to space measurements. The emphasis will be upon measurements since 1964 made outside the Earth's atmosphere, but considerable reference will be made to high energy neutron experiments conducted within the Earth's atmosphere at <10 gcm -2 altitude. A review of earlier neutron measurements of terrestrial and solar neutrons has been made by Haymes (1965).

Space Storms and Space Weather Hazards

“…This dependence is in good agreement with the data of different experiments (see e.g. Lockwood, 1973).…”

Evaluation of the neutron radiation environment inside the International Space Station based on the Bonner Ball Neutron Detector experiment

“…Albedo neutrons have higher flux in the high-latitude region (e.g. Lingenfelter, 1963;Lockwood, 1973;Lobakov et al, 1992a) so that the neutron flux in the high-latitude region is higher after the relocation in this energy range, even though its spectrum is harder, resulting in a reduced effect of the relocation. On the other hand, in the SAA region, where secondary neutrons produced by trapped protons are the major source, the neutron flux is least affected by the relocation.…”

Pre-engineering spaceflight validation of environmental models and the 2005 HZETRN simulation code

“…Such models will not be adequate for the ISS mainly oriented in the local horizontal plane along the velocity vector (minimum drag) except during battery charging. In a previous paper, we developed a dynamic/anisotropic trapped proton environment and general Hampshire (Lockwood et al 1972) geomagnetic cutoff model (Wilson et al 2006b). These models are placed in a suitable form for evaluation of the incident radiation on the bounding surface of the six-degree of freedom motion of an orbiting spacecraft for shield evaluation.…”

“…The ratio of leakage flux to integrated flux is given by the New York University (NYU) group (Korff et al 1979) in Table 1 that we use in the present model. The leakage flux was measured on the OGO-6 satellite by the University of New Hampshire (Lockwood 1972) during June 1969. The leakage flux spectrum was measured (Jenkins et al 1971, Preszler et al 1972) and calculated (Korff et al 1979) by various groups over Palestine, Texas during September 1971 and approximated by Wilson et al (1999) as…”