Variability of the minimum detectable energy of an APD as an electron detector

The purpose of this study is to evaluate the variability of the minimum detectable energy of the avalanche photodiode which would be applied for measurements of medium-energy (∼10–100keV) electrons in future magnetospheric exploration. The minimum detectable energy is affected by temperature variations as well as radiation. Our experiments and theoretical considerations show that the minimum detectable energy is significantly deteriorated at room temperature after proton irradiation of >10krad mainly due to an increase in the dark current, whereas such a degradation is less prominent when the device is cooled down to <5°C. These results provide a guideline for the thermal design of the medium-energy electron instruments especially for harsh-radiation space missions.