Sound and light from fractures in scintillators.

Prompted by intriguing events observed in certain particle-physics searches for rare events, we study light and acoustic emission simultaneously in some inorganic scintillators subject to mechanical stress. We observe mechanoluminescence in Bi4Ge3O12, CdWO4, and ZnWO4, in various mechanical configurations at room temperature and ambient pressure. We analyze the temporal and amplitude correlations between the light emission and the acoustic emission during fracture. A novel application of the precise energy calibration of Bi4Ge3O12 provided by radioactive sources allows us to deduce that the fraction of elastic energy converted to light is at least 3×10(-5).

A 2.8 K cryogen-free cryostat with compact optical geometry for multiple photon counting.

Interest in solid scintillators down to liquid helium temperature and below has grown recently, fuelled by searches for exotic processes in particle physics. We describe a closed-cycle optical cryostat with a 2.8 K base temperature and a compact optical geometry for multiple photon counting. The large numerical aperture achieved, of the order of 0.79 from the optical center to each of the two windows and amounting to 40% of the total solid angle, allows a significant gain in the efficiency of photon collection. This and the relatively big sample size that can be used facilitate the study of scintillators under gamma irradiation. These features should be an asset for multiple photon counting techniques at low temperatures.