We are developing a device for measuring the heat capacity of candidate absorber materials for gamma-ray microcalorimeters with the goal of finding materials with low heat capacity and high stopping power to improve detector efficiency. To date, only Sn has been effective as an absorber, and speculation is that other materials suffer from anomalously high heat capacities at low temperatures. The key component of the device is a low heat capacity 17 mm x 17 mm silicon platform suspended by Kevlar fibers designed for accepting 1-2 gram samples, and whose heat capacity can be characterized prior to attaching a sample. The platform has a thin film Pd/Au heater deposited directly on the silicon, and a semiconducting thermometer bonded to the surface. The heat capacity is determined from C=Gτ, where G is the in-situ measured conductance and τ is the measured temperature decay time from a step change in applied heat. For a platform without samples, decay times on the order of 0.1 to 0.05 seconds were measured, while with samples, decay times of several seconds are projected, allowing good resolution of the heat capacities. Several thermometers have been tested, including a commercial thick-film Ruthenium-oxide surface mount resistor, a germanium NTD, and a Zirconium Oxy-Nitride thin film thermometer.
July 19-24, 2009
Palo Alto, CA
Low Temperature Detectors 13
Microcalorimeter, absorber, gamma-ray spectroscopy, heat capacity, thermometry