Gamma ray Sensitivity of Superheated Liquid

INTRODUCTION The superheated drop detector (SDD) is composed of droplets of a sensitive liquid with low-boiling point and a medium supporting the droplets dispersed throughout the medium. The SDD has been mainly used for neutron dosimetry and recently also for γ -rays. However the conditions of bubble formation have been discussed for neutrons but there have been a little works for gamma-rays. We have been investigated the conditions for low LET radiation, such as protons and gamma-rays and showed octafluoropropane (C3F8, boiling point –36.7°C) as an advantageous liquid (1). The bubble formation condition is given by the energy and energy density imparted from the charged particle to the sensitive liquid. The energy density requirement means that the energy must be deposited over a definite region length, effective to produce the vapor nucleus that becomes the visible bubble. Recently for γ rays, Evans and Wang proposed the model that the energy deposition in a “cluster” including many events in proximity in a superheated liquid triggered the vaporization (2). Measurements of the γ -ray sensitivity have not been sufficiently carried out and therefore the effective length or the cluster model has not been established well. We have been developed a device to evaluate the radiation detection sensitivity by measuring the lifetime of a single liquid drop exposed to radiations. The superheated liquid drop is trapped at a specified position in its supporting material and decompressed by an acoustic standing wave field in the device and then is exposed to radiation(3). The neutron detection sensitivity of superheated liquid, trans-2-butene, has been studied by this device(4). In this study the γ -ray detection sensitivity of trans-2-butene(C4H8, boiling temperature =0.8 °C) was evaluated by the same method. The detection sensitivity was calculated also for the trapped drop irradiated with γ -rays by using Monte Carlo code, ITS3.0 and was compared to the experimentally evaluated ones.