We are developing silicon crystal acoustic detectors (SiCADs), which operate at cryogenic temperatures and use thin-films of superconducting titanium (Tc = 435 mK) to sense phonons generated when an incident particle scatters off a nucleus or electron in pure and cold (< 1 K) silicon. Our motivation for developing SiCADs includes their many direct applications to neutrino physics (e.g. to perform neutrino oscillation experiments), particle astrophysics (e.g. to measure the solar neutrino spectrum or search for the hypothetical dark matter in the universe) and solid state physics (e.g. to study phonon dynamics and focusing effects).

We have fabricated and characterized multi-channel SiCADs with phonon sensors instrumented on both sides of a Si wafer substrate, and have used these devices to detect radioactive sources of gamma and X-rays, alpha particles and neutrons with incident energies of < 6 keV to 10 MeV. We discuss our results in terms of ballistic and quasi-diffusive phonon propagation, and show evidence for ballistic phonon focusing effects in [100] silicon.