Calibration and Response of Neutron Bubble Dosimeters from Thermal Energies to 60 MeV
T.D. McLean; L.L. Romero; D.T. Seagraves; R.H. Olsher; and R.T. Devine (Los Alamos National Laboratory)
Neutron dosimeters based on superheated emulsions offer many advantages such as high neutron sensitivity, photon insensitivity (at normal operating temperatures), excellent energy response and real-time visual indication of dose. This study presents a performance evaluation of the PND* and BDT bubble dosimeters. The PND dosimeters were calibrated (bubbles/μSv) at the Los Alamos Central Health Physics Calibration Facility (CHPCF). Unlike the manufacturer's free-in-air calibration, the dosimeters were calibrated at Los Alamos on a 40x40x15cm lucite phantom. For an AmBe irradiation, the phantom albedo is found to contribute about 20% of the observed bubbles leading to a corresponding increase in the manufacturer-stated sensitivity. This finding is confirmed through experiment and Monte Carlo simulation and shown to be consistent with prior estimates of albedo response. This study also investigated the response of these bubble dosimeters over a wide range of neutron energies using well-characterized metrology-grade fields: thermal neutron data from the Geesthacht Neutron Facility (GKSS), monoenergetic data ranging from 140 keV to19 MeV from the Physikalisch-Technische Bundesanstalt (PTB) Neutron Metrology Laboratory and quasi-monoenergetic 33 and 60 MeV data from the Universite Catholique de Louvain (UCL) cyclotron. Energy response data obtained from these studies is presented and compared to previous measurements and also with the energy dependence of the Hp(10) and maximum dose equivalent (NCRP-38) dosimetric quantities. It is shown that the albedo effect on the BDT dosimeter in the thermal field is particularly pronounced. In addition, data collected at the CHPCF facility using 252Cf, D2O-moderated 252Cf and polyethylene-moderated 252Cf sources are presented and discussed. It is shown that even in heavily moderated fields, the PND-measured and calculated doses are in good agreement. * Bubble Technology Industries Inc.