EFFECTS OF TARGET FRAGMENTATION ON EVALUATION OF LET SPECTRA FROM SPACE RADIATIONS - IMPLICATIONS FOR SPACE RADIATION PROTECTION STUDIES

We present calculations of linear energy transfer (LET) spectra in low earth orbit from galactic cosmic rays and trapped protons using the H ZETRN/BRYNTRN computer code. The emphasis of our calculations is on th e analysis of the effects of secondary nuclei produced through target fragmentation in the spacecraft shield or detectors. Recent improvemen ts in the HZETRN/BRYNTRN radiation transport computer code are describ ed. Calculations show that at large values of LET (> 100 keV/mu m) the LET spectra seen in free space and low earth orbit (LEG) are dominate d by target fragments and not the primary nuclei. Although the evaluat ion of microdosimetric spectra is not considered here, calculations of LET spectra support that the large lineal energy (y) events are domin ated by the target fragments. Finally, we discuss the situation for in terplanetary exposures to galactic cosmic rays and show that current r adiation transport codes predict that in the region of high LET values the LET spectra at significant shield depths ( > 10 g/cm(2) of Al) is greatly modified by target fragments. These results suggest that stud ies of track structure and biological response of space radiation shou ld place emphasis on short tracks of medium charge fragments produced in the human body by high energy protons and neutrons. Published by El sevier Science Ltd