Benchmark Studies of the Effectiveness of Structural and Internal Materials as Radiation Shielding for the International Space Station

Abstract

Accelerator-based measurements and model calculations have been used to study the heavy ion radiation transport properties of materials in use on the International Space Station (ISS). Samples of the ISS aluminum outer hull were augmented with various configurations of internal wall material and polyethylene. The materials were bombarded with high energy iron ions characteristic of a significant part of the Galactic Cosmic Ray (GCR) heavy ion spectrum. Transmitted primary ions and charged fragments produced in nuclear collisions in the materials were measured near the beam axis, and a model was used to extrapolate from the data to lower beam energies and to a lighter ion. For the materials and ions studied, at incident particle energies from 1037 MeV/nucleon down to at least 600 MeV/nucleon, nuclear fragmentation reduces the average dose and dose equivalent per incident ion. At energies below 400 MeV/nucleon, the calculation predicts that as material is added, increased ionization energy loss produces increases in some dosimetric quantities. These limited results suggest that the addition of modest amounts of polyethylene or similar material to the interior of the ISS will reduce the dose to ISS crews from space radiation; however the radiation transport properties of ISS materials should be evaluated with a realistic space radiation field. 2

Status of Experimental Data Base Development Relevant to Space Radiation Transport and Protection

“…1 is the "odd-even" effect, where elements with even atomic number are produced in greater numbers than their odd-atomic-numbered neighbors. This effect has been noted in other data sets as well [1][2][3]5,6 , and is believed to be a consequence of nuclear structure effects manifested in final-state interactions. The ratio of fragment-production cross sections to total charge-changing cross sections for the indicated targets.…”

“…The majority of the measurements were done at 0 degrees (relative to the incoming direction of the beam). Some off-axis measurements were also made out to 10° [1][2][3][4][5] .…”

Heavy ion carcinogenesis and human space exploration

“…In fact, computer models (such as the HZETRN used by NASA or Geant4 used by ESA), accelerator and flight measurements, clearly show that light, highly hydrogenated materials provide the best protection against space radiation [104][105][106][107][108] . Liquid hydrogen should display the maximum performance as shield material.…”

Emerging Areas of Shielding Research—a Bird’s Eye View

“…However, heavy shielding does not necessarily provide better protection against the higher levels of galactic cosmic radiation in deep space, because of the secondary radiation that it might produce [24,25]. Furthermore, increasing the overall mass load of the spacecraft leads to an increase in overall costs of the mission.…”