Comparison of Radiation Induced Noise Levels in Two Ion Detectors for Shielded Space Instruments in High Radiation Fields

Radiation shielding performance and radiation induced noise levels in ion detection instruments were investigated for a high radiation field. The intensity of primary and secondary radiation behind simple shields of aluminum and tantalum were determined by Monte Carlo computer simulations. Two ion detectors were evaluated: a micro-channel plate and a custom discrete dynode electron multiplier. Europa, an icy moon of Jupiter, was selected because it is one of the most intense radiation environments in our solar system. Based on the combination of computer simulation results and experimental measurements of detector responses to electron and photon radiation, the relative radiation induced background noise was assessed to inform further instrument design considerations and performance optimization, such as anticipated signal-to-noise ratio and minimum detectable concentrations for mass spectroscopy during specific missions. Radiation detection efficiencies between the two detectors were comparable for photons and higher energy electrons, but significant differences were found for electrons with energies less than 0.5 MeV. Higher radiation induced count rates are expected for the micro-channel plate detector owing to its larger cross-sectional area. Superior instrument performance is anticipated for the custom discrete dynode electron multiplier detector in high radiation environments with the same or slightly less shielding.