Acoustic Response Of Superheated Droplet Detectors To Neutrons

The existence of dark matter (DM) was theoretically put forward more than seventy years ago. More recently, astronomical observations indicated the existence of dark matter. However, so far DM has not been experimentally detected. The search for dark matter is now one of the most active research areas for deepening our knowledge on the unknown universe. A number of innovative methods and techniques are emerging. Superheated droplet technique is relatively mature. However, it is recently revitalized in a number of frontier fields including the search for DM.In this work, the acoustic response of Superheated Droplet Detectors (SDDs) to neutrons was studied by using a252Cf neutron source and the SDDs developed by China Institute of Atomic Energy (CIAE). A sound record and analysis system was developed for the study on the characteristics of acoustic response of SDDs to neutrons.Bubble sound is one of the ways for a SDD to send out signals when liquid droplets are transformed to bubbles. The acoustic signals emitted from a detector are recorded by the sound sensor and then analyzed to distinguish the system noises and the desirable signals from all signals. Only all signals are fully characterized, can those from the real bubbles be identified and picked up from large number of noise signals originated from the system and environment. In this work, signals were characterized using a series of analytical tools, such as short-time energy calculation, FFT spectrum analysis, power spectrum analysis, decay time constant calculation, etc, and the real ones from neutron-induced bubbles identified.The frequency of bubble signals below6.5kHz was analyzed in this work, and the frequency peaks for majorities of bubbles are in the range of1-6.5kHz. There are three peaks in AR model power spectra generally, the function of AR model power density vs frequency is smoother than the one of FFT vs frequency, it is useful to distinguish frequency characteristic of signals. The duration of bubble sound is within10ms, and the value of time constant is4.1ms approximately. In addition, the group of parameters is used to pick up the bubble sound from the recorded signals in experiment.