The thermal detection efficiency for recoils induced by low energy nuclear reactions, neutrinos or weakly interacting massive particles

We report the first direct measurements on the energy dependence of the thermal detection efficiency for heavy recoiling nuclei. Two bolometers made by TeO2 crystals facing each other were operated at low temperature and read-out independently, while coincidence-anticoincidence techniques were used for particle discrimination. The experiment was carried out underground after implantation of both crystals with a source of 228Ra. The relative response for alpha particles and nuclear recoils with respect to electrons of the same energy (Quenching Factor) was found to be compatible with or slightly larger than unity. Deviations from constancy with energy of the QF for nuclear recoils in α decays of 224Ra, 220Rn, 216Po, 212Po and 212Bi were not observed.