Acoustic detection of single particles

We describe a new type of particle detector based on ballistic phonon generation in large single crystals of silicon or other low acoustic loss insulating crystals, operated at temperatures below a few kelvin. For contained events depositing an energy greater than about 1 keV, such silicon crystal acoustic detectors (SiCADs) could have spatial resolution in three dimensions of the order of ≅ 1 mm3 and energy resolution ≅ 200 eV. Superconducting tunnel junctions would be used to sense the phonons at the crystals surfaces. The improvement in tunnel junction performance with decreasing thermal quasiparticle density upon cooling would determine the detector operating temperature (≅ 50 mK). SiCADs may be particularly useful for low energy neutrino detection experiments. If a large mass could be instrumented with keV sensitivity, the coherent neutral current scattering from silicon nuclei, which is neutrino-flavor independent, could be detected, and provide a measurement of the total neutrino flux independently of complex mixing, e.g. due to the MSW effect. Other uses would include high resolution charged particle and gamma ray spectroscopy. (orig.)