MEASUREMENTS OF THE SECONDARY PARTICLE ENERGY-SPECTRA IN THE SPACE-SHUTTLE

Measurements of the energy spectra of secondary particles produced by galactic cosmic rays and trapped protons due to the nuclear interactio ns of these particles with the Shuttle shielding provide a powerful to ol for validating radiation transport codes. A code validated in this way can be used to better estimate the dose and dose equivalent to bod y organs, measurements that cannot be made directly. The principal cau se of single event upsets in electronic devices in the region of the S outh Atlantic Anomaly is secondary particles, and even in the region o f galactic cosmic radiation a significant fraction is produced by seco ndary particles. In this paper, we describe the first direct measureme nts of the energy spectra of secondary protons, deuterons, tritons, 3H e and 4He produced by galactic cosmic rays inside the Space Shuttle us ing a charged particle spectrometer. A comparison of these spectra wit h radiation transport code HZETRN showed reasonably good agreement for secondary protons. However, the code seriously underestimated the flu x of all other light ions. The code has been modified to include pick- up and knock-on processes. The modified code leads to good agreement f or deuterons and 3He but not for other light ions. This revised code l eads to about 10% higher dose equivalent than the original code under moderate shielding, if we assume that higher charge ion fluxes are cor rectly predicted by the model.