Calibration and Flight Testing of a Low-Field pMOS Dosimeter

This paper presents the results obtained from pMOS dosimeters in the Geostationary Orbit for a period of 7 years, on board European spacecraft. One dosimeter monitored radiation dose in a microwave experiment on the OTS spacecraft and five others formed a self contained `dose vs depth' monitor on the GEOS 2 spacecraft. The doses deduced from the measurements show good agreements with standard environmental prediction models for the case of thickly shielded devices (thickness above 3 mm aluminium). However, for thinner shields, dose values are generally lower than predicted. Furthermore, a large annual variation in dose is observed and this appears to have an inverse correlation with solar activity. Parallel laboratory studies included many experiments on the operation of pMOS dosimeters in "zero bias (VIO)" modes. At low doses, good linearity for threshold voltage shift vs. dose was found in this mode. These results were unexpected and may broaden the use of the MOS structure as a general-purpose dosimeter.