Study of low frequency acoustic signals from superheated droplet detector

Abstract

The bubble nucleation process in superheated droplet detector (SDD) is associated with the emission of an acoustic pulse that can be detected by an acoustic sensor. We have studied the neutron and gamma-ray induced nucleation events in a SDD with the active liquid R-12 (CCl 2 F 2 , b.p. -29.8 o C) using a condenser microphone sensor. A comparative study in the low frequency region (~ 0-10kHz) for the neutron and gamma-ray induced nucleation is presented here. From the analysis of the waveforms we observe a significant difference between the neutron and gamma-ray induced acoustic events.

Study of acoustic emission due to vaporisation of superheated droplets at higher pressure

“…Here the primary harmonic frequency (f), defined as the frequency corresponding to the highest peak in the fast Fourier transform (FFT) of the waveform, is obtained for all the acquired waveform data. For a particular SDD at a given operating condition the primary harmonic shows a distribution [13]. Here we observe that pulses from different SDDs have primary harmonics in different frequency regions [Fig.…”

“…4). For a particular type of detector, at a given operating temperature and pressure, τ usually shows a distribution [13]. The average values of τ at different pressure for R-12, R- we observe that for all the SDDs at a given operating temperature τ initially decreases with increase in operating pressure up to about 3 kg cm -2 and then it does not change much with increase in pressure.…”

“…To obtain the decay time constant (τ) of the signal, first the amplitude envelope of the waveform is calculated using the Hilbert transform of the waveform [11,13]. The decaying part of the envelope is then fitted to an exponential function , where t is the time and A is a constant.…”

“…The bubble nucleation and subsequent vaporization of superheated droplet generate an acoustic pulse which can be detected by transducers [7]. Though different techniques have been used for the detection of droplet vaporisation in superheated emulsions [7][8][9][10], acoustic detection of nucleation is still one of the important techniques used in this field [11][12][13][14]. Acoustic detection is important because of its ability to detect vaporization of a single droplet, which also could enable one to identify the nature of the particle triggering the bubble nucleation [12][13][14].…”

“…Though different techniques have been used for the detection of droplet vaporisation in superheated emulsions [7][8][9][10], acoustic detection of nucleation is still one of the important techniques used in this field [11][12][13][14]. Acoustic detection is important because of its ability to detect vaporization of a single droplet, which also could enable one to identify the nature of the particle triggering the bubble nucleation [12][13][14]. This technique can be used in discriminating bubble nucleation events due to different types of radiation [12][13][14], which already has proved it's applicability not only in studying the bubble nucleation in SDD but also in the study of bubble nucleation events in detectors used in dark matter search experiment [14][15].…”