Transition-edge microcalorimeter for tritium beta decay

We are conducting a new tritium beta-decay experiment using a cryogenic microcalorimeter. The microcalorimeter consists of a copper foil with an implanted tritium source. The foil is soldered to a thin film gold pad on a silicon wafer that is in thermal contact with an aluminum/silver bilayer transition-edge sensor. The device is voltage biased with current pulses read out using a SQUID magnetometer. The device has been tested with external sources as well as an implanted tritium source. The device is currently too slow to set a meaningful limit on the square of the neutrino mass, but can be made fast enough to set a limit on the order of 10 eV.