Analytical solution to the galactic cosmic ray cascade with applications to spacecraft shielding

摘要

As spacecraft and people venture into space, they must be protected from damaging radiation in the form of heavy, fast ions called galactic cosmic rays, coming from deep space and our own sun. Unfortunately, the material used to shield the spacecraft's interior creates a secondary radiation field that is potentially more damaging than the original radiation. The secondary radiation is caused by the collision and fragmentation of ions and shield nuclei which create lighter ions. These collisions and subsequent fragmentation continue until protons and neutrons are created. The total process is called the galactic cosmic ray cascade, and the prediction of the radiation dose from this cascade is important for the design of space vehicles. The personnel in the Environmental Interactions Branch at NASA Langley Research Center have created the HZETRN computer program to predict the dose from the galactic cosmic ray cascade. It is based on analytical and empirical high energy interaction simulations and a numerical solution to the continuous slowing down formulation of the integral Boltzmann transport equation for each ion in the and straight ahead approximation. An analytical solution to the galactic cosmic ray cascade, GIT, was created and used as a benchmark for the predecessor to HZETRN. However, all these codes assume that neutrons do not scatter. An extension to the original benchmark was created to treat neutrons realistically by coupling the GIT program to an analytical neutron transport solver based on the F(sub N) method called MGSLAB. This work will use MGSLAB and GIT to benchmark HZETRN using three sets of shield materials: lead, aluminum, and water. The resultant particle fluxes will be plotted as the comparison values since the algorithms to calculate the dose levels from the particle fluxes are not being benchmarked. This paper will describe the models and solutions used to generate the MGSLAB and GIT programs and their coupling.