The status of the bubble-damage polymer detector

Abstract

Abstract In the preceding meeting on solid state nuclear track detectors, a qualitative description was given (Ing and Birnboim, 1984) of a novel neutron detector consisting of microscopic droplets of superheated liquid dispersed in a firm elastic polymer. When neutrons interact with the detector, visible bubbles immediately appear which are immobilized by the medium to give a lasting image. Experiments showed that these detectors were insensitive to gamma radiation, but were very sensitive to Pu-Be neutrons - allowing for the measurement of less than 1 mrem of fast neutrons. In the intervening two-year period, many studies have been made into the qualitative and quantitative properties of these “bubble detectors”. Much of the work has been done in connection with the development of a personal neutron dosimeter for radiation protection purposes. These studies include the effect medium elasticity and differnt types of detector liquids, the behaviour of detectors with storage, the effect of time (during use) on detection sensitivity and on bubbles formed by neutron irradiation, the influence of ambient temperature on detector response and the effect of the volume of dispersed detector liquid on absolute detection efficiency. Studies have also been made on the neutron energy response of such detectors having different types of detector liquids. It was found that the low energy threshold of bubble detectors is determined by a particular property of detector liquids, so that detectors of desired thresholds can be produced. One type of detector, which is attractive for personal neutron dosimetry, can detect fast neutrons to below 50 keV and can also detect thermal neutrons probably because of (n,p) reactions in the detector. When worn on the body, this detector provides an essentially flat dose equivalent response from thermal to 20 MeV. Although a theoretical model of the bubble detector is still under development, the experimental results indicate that the detector is extremely promising for neutron dosimetry and other applications.