Observations and Analysis of Deep Penetrations of MeV Electrons from REPT PHA Data

The Relativistic Electron and Proton Telescope (REPT), consisting of a stack of nine aligned silicon detectors onboard Van Allen Probes, has contributed a great number of discoveries based its nominal data. However, the REPT Pulse Height Analysis (PHA) data set, which was taken every 12 milliseconds (ms), including the pulse height that is proportional to the energy deposit of each individual particle from all nine REPT detectors, has been seldom-tapped. Here we show that this data set actually provides higher energy resolution particle measurements than the typical binned data from REPT. Geant4 simulations are used to extend and improve the electron detecting capabilities of REPT using the PHA data. After replicating the nominal characteristics of REPT in the Geant4 toolbox, new channels for REPT, going from 12 electron channels to 47 and lowering the minimum energy to ~1 MeV, have been formulated. The deep storm-time penetration of MeV electrons into the slot region (2<L<3) and inner belt (L<2) has been investigated. Clear dynamic variations of MeV electrons in these regions are revealed and substantiated by quantitative analysis. This is only an example of how the REPT PHA data will enable us to quantitatively address many more various science questions.