Thermal properties of holmium-implanted gold films

The effective mass of the electron neutrino can be probed by studying the163Ho electron capture decay with cryogenic microcalorimeters. The goal is to perform a calorimetric experiment, where all the energy released in the decay is measured except for the kinetic energy of the neutrino. To achieve such a goal, multiple approaches are being investigated to enclose the radioactive source in a microcalorimeter absorber without affecting the thermal properties of the absorber material. One such approach is to implant the radioactive isotope into a gold absorber, as gold is successfully used in similar applications. We measured the heat capacity of gold films, implanted with various concentrations of holmium and erbium (a byproduct of the163Ho fabrication), in the temperature range 70-300 mK. Our results show that the specific heat capacity of the films is not affected by the implant, making this a viable option for a future experiment. We also verified that the implant does not affect the crystal structure of the gold film. © 2014 Springer Science+Business Media New York.