(a) The geometry of the sensitive cube: two layers of Si pixel detectors are placed on each facet of a Ti box, which contains a plastic scintillator. At the bottom, a silicon photomultiplier in touch with the plastic scintillator and beneath them one layer of Si. (b) The die of the Si active pixel sensor. (c) Visualization of the tracks of secondary particles produced when a 10 GeV ⁵⁶Fe ion hits the device. Gray: the ⁵⁶Fe track; red: photon tracks; green: neutron tracks; blue: proton tracks.