This experiment package was changed before launch and then became a group of Cerenkov and solid-state silicon sensors based on earlier Pioneer 10/11 experiments (NSSDC ID 72-012A-05 and 73-019A-05). It was designed to measure energetic electrons above 200 keV and higher energy electrons and protons in trapped radiation belts. The two Cerenkov sensors employed alcohol-water and fused-silica radiators, viewed by photomultiplier tubes, with respective refractive indices of 4/3 and 3/2 and with corresponding proton energy thresholds of 440 and 320 MeV. These sensors were also sensitive to electrons above 7-8 MeV. An electron scatter sensor measured electrons above 200 keV by using a V-shaped brass collimator and a gold aperture plug to guide scattered electrons into the silicon E detector. A similar detector (M) behind E was heavily shielded and responded to penetrating electrons above 35 MeV and protons above 80 MeV. A photometer system was also included in this package to view GTO chemical releases and measured narrow-band emissions from lithium, barium, and europium in four wavelength channels simultaneously using a split-anode microchannel plate photomultiplier tube. This experiment was part of the SPACERAD project sponsored by AFGL.