One interesting use of germanium detectors is in the study of coherent neutrino scattering. The way existing neutrino detectors work is that they wait for a neutrino to collide with a nucleon, destroying the neutrino and transferring all of its energy into the target material. This process (called inverse beta decay) makes for a bright signal, but it doesn’t happen often, which is why neutrino detectors have to be huge.
However, there’s another interaction we can exploit to find neutrinos. In coherent neutrino scattering (shown schematically at left), a neutrino interacts coherently with all the nucleons in a target nucleus, transferring just a little of its kinetic energy to the nucleus before continuing on its way. This happens much more often than inverse beta decay, but results in a smaller energy deposition. Therefore, a detector sensitive enough to measure the deposition of tiny amounts of energy (just 10’s or 100’s of eV) could be used as a neutrino detector much smaller than existing technology allows.
An especially important application of this technology is in the field of nuclear safeguards. Since nuclear reactors make copious antineutrinos, an easy-to-transport neutrino detector would make it possible to monitor nuclear reactors for compliance without interfering with–or relying on–the reactor’s operators. The graph at right shows a calculation of how many neutrinos could be detected per kg of germanium in the detector for a typical reactor installation.