Bd-100: the Chalk River Nuclear Laboratories’ Neutron Bubble Detector*

The BD-100 is a neutron bubble detector which is available commercially from Chalk River Nuclear Laboratories, Canada. The detector consists of tiny superheated liquid droplets that are dispersed throughout a firm elastic polymer. The polymer is contained in a small capped and sealed glass (glass detector) or plastic (plastic detector) test tube. A low boiling point liquid floating above the polymer exerts adequate pressure on it so as to keep it in a radiation insensitive state. The detector is sensitized by removing the cap and discarding the liquid. Upon neutron irradiation visible bubbles are formed in the detector, the number of bubbles being a measure of the neutron dose equivalent. One hundred percent of the sensitivity is obtained when the detector is used within eight hours after sensitization. The sensitivity is dependent upon temperature at the time of irradiation. Studies performed with the glass detectors indicate that bubble size distribution and concentration are nonuniform within the irradiated detector. The bubbles continue to grow in size with time. Plastic and glass detectors exposed on an ICRU phantom to PuBe neutrons had sensitivities within 16 percent of the claimed values. The response of the glass BD-100 was fairly linear between neutron dose equivalents of 40 and 170 ~SU. --Studies on the effect of storage time prior to and after irradiation showed that the detector did not undergo any fading for a period of five months. The sensitized detector is sensitive to impact and thermally unstable at temperatures of 48” C or greater. The BD-100 is insensitive to 6oCo-gamma ray s but responds to photons of energies 6 MeV or greater. Results of irradiation in electron beams of energies 9 to 20 MeV are also presented. Exposure of detectors mounted on a phantom to neutron sources of average energies ranging from 0.5 to 4.5 MeV indicates that the dose equivalent response of BD-100 exhibits some energy dependence. L.. ;.rSubmitted for Publication *Work supported by the Department of Energy, contract DE-AC03-76SF00515. r