Surface sensitivity in large mass bolometers: Discrimination of the origin of events

During the last decades, low temperature detectors have undergone a considerable growth and are now widely acknowledged as useful instruments in many fundamental physics experiments. In this field, the phonon mediated particle detectors known as bolometers are remarkable and are successfully used in various branches of physics research for their good sensitivity, energy resolution and flexibility in the choice of the constituting materials. Bolometers have proved to be powerful devices for radiation detection; in particular, they are able to detect Gamma rays with resolutions comparable to those obtained with the best Ge diodes. They are also suited for applications in the area of nuclear and particle physics, like the study of rare events or dark matter. Although an effective technique, the use of bolometers in the specific field of the search for neutrinoless double beta decay is affected by the lack of spatial resolution. This results in the expected signal of this rare decay hidden under an indistinguishable background due to possible surface radioactive contaminations in the materials facing the detectors. An approach to this problem is to make bolometers surface sensitive by applying ultra-pure crystalline foils on the main detector through direct thermal contact and by operating them as active shields. In this contribution we present for the first time surface sensitivity achieved with large mass TeO2 bolometers (similar to 800 g) operated underground at similar to 10 mK, dedicated to the detection of neutrinoless double beta decay of Te-130. Our encouraging measurements suggest that this could be a viable method for the discrimination of background events.