Comparison of different methods of estimating the effective dose and the ambient dose equivalent for neutrons from measured prompt gamma intensities

摘要

Estimations of the ambient dose equivalent H* (10) and the effective dose (anterior-posterior) E_(AP) from prompt gamma intensities are investigated theoretically using Monte Carlo simulations. The system considered consists of a NaI(Tl) gamma detector to measure prompt gamma intensities emitted due to neutron irradiation from a high density polyethylene (HDPE) cylinder embedded in a hollow borated-HDPE cylinder and covered by a layer of lead. A comparative evaluation of different computational techniques of dose estimation, such as, the multiple linear regression method, the detector response-matrix inversion method and the convolution of the unfolded neutron energy distributions with the fluence to dose conversion coefficients (DCC) provided by the International Commission on Radiological Protection (ICRP) is done. The dose estimations are done using the prompt gamma responses (response matrix) obtained for the five distinct gamma peak intensities (boron, hydrogen, carbon and 2 from lead) emitted from the system for incident mono-energetic neutrons ranging from 0.01 eV to 1 GeV. Different workplace neutron spectra are used for the estimation of ambient dose and effective dose to evaluate performances of these three dose estimation methods. The doses (H* (10) and E_(AP)) estimated using the convolution of the unfolded neutron spectra with the DCC-ICRP result in satisfactory and accurate agreement with the actual dose, followed by the estimated dose obtained from the regression analysis.