Scintillating bolometers: a technique promising zero background

Bolometers are amongst the most interesting nuclear detectors for the conduction of next-generation Double Beta Decay searches. A bolometer consists of an energy absorber linked to a temperature sensor. The signal, collected at very low temperatures (typically <20 mK for large bolometers), consists of a thermal pulse registered by the sensor, which can be either a small semiconductor crystal, a thin superconductive film or a metallic magnetic thermometer. The majority of the most promising high Q-value candidates can be studied with the bolometric technique in the so-called “source=detector” approach, joining high energy resolution and large efficiency. High Q-values are preferred, as they lead to larger phase space and to lower background.The highest relevant gamma line in natural radioactivity is the 2615 keV line of 208Tl in the 232Th decay chain.

Therefore, a detector based on a Double Beta emitter with a Q-value above 2615 keV represents an optimal starting point for a future experiment. However, the energy region above 2615 keV is dominated by alpha particles. Hence derives the power of scintillating bolometers, the technology proposed for LUMINEU. Since the alpha light yield is generally appreciably different from the beta/gamma light yield at equal deposited energy, while the bolometric thermal response is substantially equivalent, the simultaneous detection of scintillation (light channel) and thermal signals (heat channel) can reject fully alpha background. The isotope proposed for LUMINEU is Mo-100, with a Q-value of 3034 keV. The scintillating crystals to be operated as bolometers are based on the compound ZnMoO4.