Determination of nucleation efficiency of polydisperse superheated emulsions using an active device Method

Abstract

Superheated emulsion detector (SED), a well-known detector for neutrons, photons etc., is the emulsion of superheated liquid droplets dispersed in visco-elastic gel (known as superheated drop detector, SDD) or in soft polymer matrix (known as bubble detector, BD). The present work has been performed by using SDD, fabricated in our laboratory by simple method of emulsification, which produces polydisperse sample (droplets of different sizes). When SED is exposed to energetic radiations, sufficient amount of energy deposition inside the liquid can cause droplet nucleation. In the present work we have studied nucleation in some of the SEDs by an indigenously designed activedevice using 241 Am-Be neutron source and 241 Am and 137 Cs gamma sources. One of the important observations of the present investigation is the droplet volume distribution in SED. The effect of volume distribution on the droplet lifetime distribution is proposed here. The proposed model although can explain most of the features of the experimental data, but to explain the presence of initial sharp rise in the data one needs more clarifications to understand the physics of nucleation. The most important observation is the presence of more than one metastable state (here two states are considered) in SED. To the best of the author’s knowledge, present investigation is completely new and never been observed in the past. A new model known as the “isolation approximation” model is proposed considering the effect of second metastable state. The model corrected the existing model to get the nucleation efficiency and obtained vi the temperature threshold neutron energy relationship for R-12 and R-114 SED. The gamma energy dependence of detection efficiency of R-12 has also been studied by varying temperature. The present work gives new concept of two metastable states of SED and gives a more complete picture in understanding the physics of nucleation of superheated droplets. Although not as a part of the investigation proposed in the thesis, we have made some theoretical investigation to estimate the limit of superheat of the liquid. A simple model based on a more valid premise and without having any adjustable parameter has been proposed and verified with other existing model.