New insights into particle detection with superheated liquids

We report new results obtained from calibrations of superheated liquid droplet detectors used in dark matter searches with different radiation sources (n, α, γ). In particular, detectors were spiked with α-emitters located inside and outside the droplets. It is shown that the responses have different temperature thresholds, depending on whether α-particles or recoil nuclei create the signals. The measured temperature threshold for recoiling ²¹⁰Pb nuclei from ²¹⁴Po α-decays was found to be in agreement with test beam measurements using mono-energetic neutrons. A comparison of the threshold data with theoretical predictions shows deviations, especially at high temperatures. It is shown that signals produced simultaneously by recoil nuclei and α-particles have more acoustic energy than signals produced by one or the other separately. A model is presented that describes how the observed intensities of particle-induced acoustic signals can be related to the dynamics of bubble growth in superheated liquids. A growth scenario that is limited by the inertia of the surrounding liquid shows a trend that is supported by the data. An improved understanding of the bubble dynamics is an important first step in obtaining better discrimination between particle types interacting in detectors of this kind.