Deriving SEP Proton Fluxes with the JUICE Radiation Environment Monitor: Response-Matrix Inversion and Near-Conjunction Validation with IREM

Radiation environments driven by solar energetic particle (SEP) events are a key risk for deep-space missions, and robust flux retrievals are essential for both operations and long-term environment models. We present an end-to-end proton flux inversion pipeline for the Radiation-Hard Electron Monitor (RADEM) on ESA’s JUICE mission, focusing on the proton detector channels in the nominal configuration. We apply a normalization that converts Geant4 simulation counts into calibrated response-matrix elements, consistent with the General Particle Source (GPS) setup (surface source on a sphere) and a cosine-weighted angular distribution within a finite cone. The response matrix is then used with multiple inversion approaches and time-averaging schemes to retrieve proton intensities in predefined energy bands.

To validate absolute scaling and spectral behavior, we compare RADEM-derived proton time series for selected SEP events with contemporaneous IREM (INTEGRAL Radiation Environment Monitor) Level-2 proton differential fluxes integrated over matching energy bands. The comparison includes quiet-time intervals before and after each event and focuses on periods when JUICE and IREM were in close spatial proximity. We discuss practical sensitivities across the tested inversion approaches and outline next steps. This work provides a reproducible foundation for SEP analyses with RADEM and supports broader heliospheric energetic particle studies across missions.