The basic idea of EPT is to constitute a block with only a small number of active detectors (around 10) separated by layers of well chosen (and less expensive) inert materials (not active) with calibrated widths that we call digital absorber modules.
The measurement of the penetration distance is obtained by counting simply the number of detectors that gave a signal or more precisely by registering the so-produced binary number. We know then that the energy of the particle is included in a specific energy range called channel.
The electronic treatment of the signal onboard the satellite is then simply the registered number (of hit detectors) corresponding to the energy of each incident particle. The conversion of this binary number in energy is known by the calibrations realized at the ground with particle accelerators before the launch.
In the space radiation belts the EPT instrument will measure the high energy fluxes of:
Due to the widely varying fluxes of electrons, protons and heavy ions within the radiation belts, the instrument has a stunning in-flight particle discrimination capability that provides more precise measurements than those made by previous detectors.
The observations will be used to complete the empirical dynamic model of the space radiations developed at UCL and BIRA-IASB to predict the flux variations during geomagnetic storms.
This spectrometer will also provide new measurements of the spectra of electrons, protons and heavier ions at high energy ranges. This is crucial because a considerable part of the range of the NASA radiation belt models (especially at high energy) was achieved by extrapolation.