Determination of the conventional true value of gamma-ray air kerma in a minitype reference radiation

Abstract

To develop mobile calibration equipment for gamma-ray dose or dose rate meters in the field of radiation protection, a minitype reference radiation (MRR) of 0.5m×0.5m×0.5m cube was set up and used for investigation. Two types, which add up to 12 daily used gamma-ray dose rate meters, were used as samples to determine the conventional true value of air kerma (CAK) at the point of test in the MRR. A gamma-ray spectrometer was also used to monitor the scattering gamma rays in the MRR, which were applied further to characterize the disturbance of scattering gamma ray in CAK determination. On the basis of the sample data sets of CAKs, scattering gamma spectra and air kerma values at the point of test without sample meters, a CAK prediction model at the point of test was developed by the least square support vector machine, which is a multiple nonlinear regression method. For reducing the amount of data and improving the regression efficiency, principal component analysis (PCA) was used to extract feature components from the scattering gamma-ray spectra before regression. A relative standard uncertainty of 4.65% was achieved in determining CAK in the MRR using the constructed prediction model.