Electronic neutron personal dosimetry with superheated drop detectors

The prototype of an electronic personal neutron dosemeter based on superheated drop detectors is presented. This battery operated device comprises a neutron sensor, bubble-counting electronics and a temperature controller ensuring an optimal dose equivalent response. The neutron sensor is a 12 ml detector vial containing an emulsion of about 50,000 halocarbon-12 droplets of 100 microns diameter. The temperature controller is a low-power, solid-state device stabilising the emulsion at 31.5 degrees C by means of an etched foil heater. The microprocessor controlled counting electronics relies on a double piezo-electric transducer configuration to record bubble formation acoustically via a comparative pulse-shape analysis of ambient noise and detector signals. The performance of the dosemeter was analysed in terms of the requirements presently developed for neutron personal dosemeters. The detection threshold is about 1 microSv, while the personal dose equivalent response to neutrons in the thermal to 62 MeV range falls within a factor 1.6 of 13 bubbles per microSv.