Neutron detection based on superheated materials

The environmental and radiation responses of the active personnel dosimeter/superheated drop detector (APD/SDD) combination have been evaluated at the Pacific Northwest Laboratory (PNL) for the US Department of Energy's Neutron Measurement and Evaluation Program. Results of the evaluation and possible improvements for the current system are discussed. The APD/SDD system provides real-time indication of dose equivalent resulting from neutron exposure. The APD/SDD has good neutron sensitivity and a practical readout system. The SDD is insensitive to moderate pressure changes and vibration and is not affected by M150 and H150 X-rays or intermittent use within a reasonable time period. The energy response of the SDD agrees well with recommended response. The linearity of the SDD decreases with increasing accumulated dose equivalent due to the reduction of superheated droplets. The SDD is also severely temperature-dependent. The useful range is roughly 0-150 mrem; use at higher levels requires a manufacturer-supplied calibration curve. The temperature sensitivity requires use in a relatively stable thermal environment, or the use of a thermal isolation chamber to keep the APD at a relatively constant temperature. >