Determination of 7-30 MeV electron intensities: ULYSSES COSPIN/KET Results

Abstract

The COsmic and Solar Particle INvestigation Kiel Electron Telescope was designed to measure electrons from a few MeV up to a few GeV using particle energy loss and particle velocity measurement techniques. Unfortunately the KET channel measuring electrons in the energy range from 7-170 MeV is contaminated by a γ-ray background (Ferrando et al., 1996). Besides a possible slight contribution from the RTG radiation, we have shown that this background is mainly generated by high energy protons interacting with the spacecraft matter. Such γ-rays can enter "unseen" the instrument and are partially converted into electrons in the calorimeter consisting of a high Z lead fluoride Cherenkov detector. Such electrons could be counted in the 7-170 MeV electron channels. In this paper we present a method to quantify this background and thus determine lower and upper limits for the intensities of electrons with energies from 7 to 30 MeV. Our analysis shows that above 30 MeV the background in this specific channel is so dominant, that no correction is possible.