Mv. shamRcr. Vol. 17, No. 2,pp.(2)53-&2&;= zyxwvutsrqponm 0273-l 177(!S)OO512-4 Ritdaiin~Btitain. 0273-l177196 $9.50 + 0.00 SECONDARY RADIATION ENVIRONMENTS IN HEAVY SPACE VEHICLES AND INSTRUMENTS C. S. Dyer,* P. R. Truscott,* H. Evans,* A. J. Sims,* N. Hammond** and C. Comber** * zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Space and Communications Deparbnent,Defence Research Agency, Famborough, Ham GU14 MD, U.K. ** EDS(UK), Fleet, Ham, U.K. ABSTRACT Secondary radiations produced by the interactions of primary cosmic rays and trapped protons with spacecraftmaterials and detectorsprovides an important,and sometimesdominaut, radiation environment for sensitive scientific instruments and biological systems. In this paper the success of a number of calculations in predicting a variety of effects will be examined.The calculationtechniques include Monte Carlo transport codes and semi-empirical fragmentation calculations. Observations are based on flights of the Cosmic Radiation Environment and ActivationMonitor at a number of inclinations and altitudes on Space Shuttle. The Shuttle experimentsincluded an active cosmic-raydetector as well as metal activation foils and passive detector crystals of sodium iodide which were counted for induced radioactivity soon after return to earth. Results show that cosmic-raysecondariesincrease the fluxes of particles of linear energy transfer less than 200 MeV/(gm cm-‘),while the activationof the crystals is enhanced by about a factor of three due to secondary neutrons. Detailed spectra of induced radioactivity resulting from spallation products have been obtained.More than a hundred sign&ant radioactivenuclides are included in the calculation and overall close agreementwith the observationsis obtained. INTRODUCTION The increasing use of heavy space vehicles and payloads means that it is no longer adequate to predict radiation effects based on primary radiationalone. Pathlengthscan readily approach and exceed 100 gm cm-*,which is of the order of the depth at which the Pfotzer maximum of cosmic-ray secondaries is produced in the atmosphere.Thus while shielding can be beneficial against radiation belt and solar flare particles of energies up to a few hundred MeV,it can be detrimentalwhen consideringthe very energetic cosmic rays of several GeV. Effects of concern include biological dose to astronauts, where secondary neutrons and cosmic ray fragments are important,as well as induced radioactivityand secondary particle background in sensitive spaceborne instrumentation. To assess secondary particle effects, radiation transport codes must be employed. These may be either stochastic or deterministicand associatedcross-sections may be determined either semi-empiricallyor by simulation. In this paper we compare such calculations with measurements obtained using the Cosmic Radiation Environment & ActivationMonitor(CREAM) carriedon Space Shuttle missions.The CREAM experiment has also been carried on supersonic and subsonicaircraftat 55000 and 35000feet respectively thus extending observations to the full range of shielding depths. CALCULATIONS Primary and secondary particle propagationand interactionsare modelled using the lntegrated Radiation (C)British Crown Copyright Published withthe permission of Her Britannic Majesty’s Stationery Office (2)53