Effect of lead converter on superheated drop detector response to high-energy neutrons

The response of superheated drop detectors or bubble detectors (BDs) was measured for quasi-monoenergetic neutron beams in the 40–75 MeV range and the effects of a lead-converter enclosing the detector introduced to extend the response to the high-energy region were discussed. The experiments were performed in the quasi-monoenergetic neutron beam field at the AVF cyclotron facility, TAKASAKI Ion Accelerator for Advanced Radiation Application (TIARA) of Japan Atomic Energy Research Institute(JAERI). Monte Carlo calculations by MCNPX code were carried out to estimate the lead-converter effect on neutron spectra in a detector exposed to 40–75 MeV quasi-monoenergetic source neutrons. The calculations indicated an increase in the energy ranges of the neutrons of 0.1–10 MeV and this can be expected to increase the number of bubbles produced in the detector. Experimental results showed that the sensitivity was lowered to about a half the nominal sensitivity and that a 3 cm thick lead-converter could compensate for the sensitivity decrease in the experimental energy region.