ACTIVE NEUTRON SPECTROMETRY WITH SUPERHEATED DROP (BUBBLE) DETECTORS

A new approach to neutron spectrometry has been developed in a joint p roject by DCMN Pisa and PTB Braunschweig. The system relies on the use of superheated drop (bubble) detectors and the thermodynamic control of their detection thresholds. This is the result of investigations in to the physics of these detectors combined with extensive experimental work on their response to neutrons. These studies indicate that the h igher the degree of superheat of a detector, the lower the minimum ene rgy that secondary charged particles, and therefore primary neutrons, must impart to the droplets in order to nucleate their evaporation. Th erefore, by controlling the temperature of the detectors, accurately d efined detection thresholds, virtually any desired one, can be generat ed in the 0.01-10 MeV neutron energy range. An active prototype instru ment has been developed: bubbles are counted acoustically and temperat ure regulation is achieved by means of thin heating strips. Tests with reference neutron spectra show that the system is suitable for few-ch annel spectrometry and may be useful for radiation protection dosimetr y. Appropriate unfolding algorithms are currently investigated, to be ultimately implemented in an automatic device.