Neutron Environment Calculations for Low Earth Orbit

Abstract

The long term exposure of astronauts on the developing International Space Station (ISS) requires an accurate knowledge of the internal exposure environment for human risk assessment and other onboard processes. The natural environment is moderated by the solar wind, which varies over the solar cycle. The HZETRN high charge and energy transport code developed at NASA Langley Research Center can be used to evaluate the neutron environment on ISS. A time dependent model for the ambient environment in low earth orbit is used. This model includes GCR radiation moderated by the Earth's magnetic field, trapped protons, and a recently completed model of the albedo neutron environment formed through the interaction of galactic cosmic rays with the Earth's atmosphere. Using this code, the neutron environments for space shuttle missions were calculated and comparisons were made to measurements by the Johnson Space Center with onboard detectors. The models discussed herein are being developed to evaluate the natural and induced environment data for the Intelligence Synthesis Environment Project and eventual use in spacecraft optimization.

3DHZETRN: Shielded ICRU spherical phantom

“…This was first accomplished by Clowdsley et al (2000Clowdsley et al ( , 2001 and later improved by Slaba et al (2010a) with demonstrated improved results (Slaba et al, 2010aHeinbockel et al, 2011aHeinbockel et al, , 2011b. In this case, propagation of the isotropic neutrons is represented in two directions by Ω 1 = Ω 0 and Ω 2 = −Ω 0 .…”

“…Yet, the low-energy protons and other light ions produced in tissue through neutron collisions contribute significantly to biological injury and must be accounted. This was the basis of the studies of Heinbockel et al (2003) starting with Clowdsley et al (2000Clowdsley et al ( , 2001 using the NUCFRG2 database and the light ion cross sections of Cucinotta (Cucinotta and Dubey, 1994;Cucinotta et al, 1998), with recent improvements provided by Slaba et al (2010a). Herein, we will concentrate on extending the transport formalism to full 3D using the NUCFRG3 database.…”

“…as first investigated by Clowdsley et al (2000Clowdsley et al ( , 2001 using multigroup methods and recoupling to the light ions using an analytic solution as a quadrature over the induced light ion source term. These types of approximations were further studied and improved by Slaba et al (2010aSlaba et al ( , 2010b and tested by Heinbockel et al (2011aHeinbockel et al ( , 2011b.…”

Earth-Moon-Mars Radiation Environment Module (EMMREM)

“…Several nuclei with smaller primary abundances or production cross-sections of scientific interest are also included in the expanded HZETRN code. More recently, HZETRN has been extended to include angular deflection of heavy ions through multiple scattering [32] and bi-directional neutron transport [33]. The ESMD is making a large investment in HZETRN developments for engineering shielding analysis applications.…”

Ion Beams for Space Applications

“…It should be mentioned that sometimes considerable amounts of neutrons can be encountered in Low Earth Orbit (less than 1000 km altitude). When they occur, they are albedo neutrons coming from earth as a result of the interaction of GCR with the earth atmosphere [6].…”