Neutron Ambient Dosimetry with Superheated Drop (Bubble) Detectors

A prototype neutron area monitor was developed which improves the performance of superheated drop detectors based on halocarbon-12. The detectors are thermally controlled: this removes external temperature effects while ensuring dose equivalent response optimised with respect to its energy dependence. The system was first characterised through calibrations with monoenergetic neutron beams. In the intermediate energy range, where experimental investigations were not possible, Monte Carlo response calculations were carried out. The prototype was then extensively tested by means of simulated and in-field irradiations with broad neutron spectra. All these tests indicated a remarkably constant dose equivalent response regardless of the neutron energy distributions. The current device is a fairly delicate system which can be operated reliably when environmental conditions are not extreme. Nevertheless, when it was possible to employ it, this monitor demonstrated an accuracy far superior to that of conventional meters used in routine surveillance.