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We report on the superconducting properties of amorphous NbSi thin films. The normal-state resistance and critical temperatures can be separately adjusted to suit the desired application. Notably, the relatively low electron-phonon coupling of these films makes them good candidates for an 'all electron bolometer' for Cosmological Microwave Background radiation detection. Moreover, this device can be made to suit both high and low impedance readouts. [ABSTRACT FROM AUTHOR]

We report the performance of two prototype TeO2 macrobolometers, operated at ∼25 mK, able to identify events due to energy deposited at the detector surface. This capability is obtained by thermally coupling thin Ge active layers to the main energy absorber of the bolometer, and is demonstrated by irradiating the detectors with α particles. The temperature variations of the main absorber and of the active layer are measured independently with doped Ge thermistors. These results show clearly that an intrinsic limitation of monolithic low temperature calorimeters, e.g., the impossibility to give information about event position, can be efficiently overcome using composite structures. [ABSTRACT FROM AUTHOR]

Abstract: Experiments searching for rare events, such as neutrinoless double beta decay and interactions of dark matter candidates, require extremely low levels of background. When these experiments are performed using macro-bolometers, radioactive contamination near the surfaces is of particular concern. For a bolometric neutrinoless double beta decay experiment, it can cause counts in the spectral region where the signal is expected, while for a dark matter experiment which exploits ionization signals for particle identification, it originates an incomplete charge collection simulating a nuclear recoil. In order to control the effects of surface contamination, we developed a novel technique that uses composite macro-bolometers to identify energy depositions that occur close to the surfaces of materials immediately surrounding the detector. The composite macro-bolometer proposed and studied here consists of a main energy absorber that is thermally coupled to and entirely surrounded by thin absorbers that act as active shields. Surface energy depositions can be rejected by the analysis of simultaneous signals in the main absorber and the shields. In this paper, we describe a full thermal model and experimental results for three prototype detectors. The detectors consist of Ge, Si, or TeO2 thin absorbers as active shields, all with TeO2 crystals as main absorbers. In all cases, the surface event rejection capability is clearly demonstrated. In addition, simulations and preliminary results show that it is possible to detect energy depositions that occurred on the shields without separate readout channels for them. The energy depositions in the shields are distinguished from those in the main absorber through pulse shape discrimination. This simplification makes this technique a viable method for the rejection of surface energy depositions in next-generation bolometric double beta decay searches, such as possible extensions or upgrades of the CUORE experiment. [Copyright &y& Elsevier]

In this work, we report on the Czochralski growth of Li 2 MoO 4 crystals up to 230 g for heat-scintillation cryogenic bolometers likely to be used in astroparticle physics and neutron spectroscopy. Their transmission properties, radiopurity levels and detector behavior characterizations were carried out in order to validate the crystal growth process. The melting characteristics, the partition coefficients of a broad range of impurities, the thermal expansion (lattice parameters and dilatometry) and specific heat properties of the crystals were measured, over a broad temperature range for the last two, providing new data likely to be used in crystal growth process numerical simulations. We also investigated the crystal growth of Li 4 Mo 5 O 17 and determined its melting behavior and specific heat. The physical properties directly relevant to heat-scintillation cryogenic bolometers of Li 2 MoO 4 and Li 4 Mo 5 O 17 are discussed in the context of the current materials developed for such applications. [ABSTRACT FROM AUTHOR]

Abstract: One of the critical issues while operating bolometric detectors over periods of time of 1 year or more consists of keeping their response stable within a 0.1% level, despite the unavoidable temperature fluctuations of the cryogenic set-up. By using an energy pulser, which periodically delivers a fixed amount of energy in the absorber, it is possible to stabilize the response of the bolometers. A stabilization technique using heating devices, made up of heavily doped semiconductor material (well above the metal-to-insulator transition), has been developed in the framework of the CUORE experiment. In this paper we describe in detail the procedure for the realization of the heating elements, based on silicon planar technology. We then report on the multi-step low temperature characterization (77K, 4.2K, 1.5K, 35mK) of the heaters. Finally, an example of achieved stabilization for a CUORE-like detector is reported. The heaters tested at show less than 0.5% change in resistance between and 3mV, and less than 1% change in value between 50mK and 800mK. In particular, the resistance change between 4.2K and 1.5K is less than 0.1%. [Copyright &y& Elsevier]