Hermann J. Schaefer’s scientific contributions

Nuclear emulsion recordings of radiation exposure of Apollo 11 astronauts on moon

Ilford G.5 emulsions in radiation packs carried by the astronauts in their space suits on the Earth-orbital mission Apollo VII and the first lunar mission Apollo VIII were scanned for tracks of heavy nuclei. As the 'microbeam' effects of heavy nuclei in living tissue center upon the high Z numbers, the scan was limited to Z numbers of 20 and higher. Greatly different fluxes are found on the two missions. The findings demonstrate the great difference in the make-up of the radiation environment in a near-Earth orbital and a deep-space mission and point out the need for a better understanding of the radiobiological significance of total body irradiation with heavy nuclei if the exposure status of an astronaut from accumulated exposures to the deep-space radiation environment is to be assessed accurately.

Earlier evaluations of small nuclear emulsion sheets flown on the astronauts' bodies during the 14-day Gemini VII mission had been limited to grey tracks which allowed grain counting. This report provides data on the population of heavy tracks. By comparing visual appearance of the diameter of the solid silver core and of the delta ray aura with tracks of known Z, tracks of Z > or = 20 were identified and counted. A total of 287 such tracks yielded a mission flux of 38.4 nuclei/sq cm of Z > or = 20, corresponding to a tissue dose of 1.35 millirads. Theoretical assessment of the flux by considering the geomagnetic latitude profile of the mission leads to 74.8 nuclei/sq cm of Z > or = 20. The difference closely matches the expected attenuation due to the inherent shielding of the vehicle and the self-shielding of the astronauts' bodies if one assumes a collision mean free path of 14 g/sq cm for nuclei of Z > or = 20. The results confirm earlier estimates that galactic heavy nuclei contribute less than 5 per cent to the total absorbed dose. (Author)