Innovations in low-temperature calorimeters: surface sensitive bolometers for background rejection and capacitive bolometers for higher energy resolution

Abstract

In this contribution, we describe two innovations of the structure of large mass bolometers, proposed by the cryogenic group of the Insubria University (Como) and developed in collaboration with the Firenze group. First, up to now, low temperature calorimeters do not have any sort of spatial resolution. This means that it is not possible to reject events coming from the material that faces the detectors (holder, refrigerators shields, ...). In order to cope this problem, we developed a new kind of composite bolometers able to discriminate, by means of active ultra-pure semiconductor shields, external surface events from those coming from the absorber bulk. A second innovation that we discuss here concerns the temperature sensors. Presently, neutron transmutation doped Ge thermistors are the most common kind of phonon sensors. Unfortunately, this kind of readout dissipates power on the detector because of the thermistor biasing and also introduces a Johnson noise term. To improve energy resolution we studied and test the application of capacitive sensors that in principle could allow us to achieve a better signal-to-noise ratio. Modeling, simulations and first encouraging measurements on surface sensitive bolometers will be discussed along with preliminary results on capacitive sensors.