Abstract
We have studied the acoustic behavior of an a-SiO2 composite torsional oscillator in the temperature range between 1 and 100 mK. At higher temperatures, the acoustic properties of amorphous solids are well described by the ‘tunneling model’. However, below 10 mK it was found that the resonance exhibited a non-Lorentzian shape and was highly distorted by random ‘noise’. We attribute this stochastic noise—‘transients’ to interactions of a-SiO2 with ambient γ quanta present in the laboratory. By shielding the cryostat with a 5 cm thick lead wall we were able to reduce the number of transients. On the other hand, a deliberately introduced 6.1μCi 22Na source of γ radiation caused the opposite effect. We interpret the transients in the framework of local heating caused by the interaction between photons and amorphous SiO2 which changes the elastic properties of the oscillator. Our findings have potential applications for particle detection.
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