Phonon mediated position resolved detection of alpha -particles with superconducting tunnel junctions

The authors report that 5-MeV alpha -particles bombarding the back of a silicon wafer (3-mm thick) through two collimating holes of 0.75-mm distance were simultaneously detected with three Al tunnel junctions (5-mm separation) at the opposite face of the wafer. Signals from the junctions originated from phonons traveling ballistically from the region of absorption to the crystal surface. The highly anisotropic phonon flux that arise from phonon focusing effects and the relative timing of pulses from different junctions allowed a clear separation of events from alpha -particles passing through different holes. >