Abstract
High-energy neutrons (En > 10 MeV) are relatively penetrating and give a significant dose contribution due to the high fluence-to-dose conversion coefficients, but lead to a negligible response in most conventional moderated-type neutron detectors. A dose correction approach following ISO-8529 calibration method with was proposed based on response functions of Bonner spheres, fluence-to-dose conversion coefficients, and various spectra in workplaces presented in IAEA Technical Reports Series No. 403. By comparing 252Cf-calibrated dose responses with reference values based on fluence-to-dose conversion coefficients, the effects of the neutron spectrum on the accuracy of dose measurements were investigated and workplace-specific correction factors were suggested for conventional neutron dosemeters when used in environments with high-energy neutrons. The suggested spectral correction factors were first established according to the flux percentages of high-energy neutrons in workplaces. Alternatively, another high-energy neutron (HEN) index was also established to facilitate the dose correction in practical situations, where the workplace-specific HEN index was determined based on quick measurements, the ratio between the measured responses of two Bonner spheres (the 4P6_8 extended-range sphere versus the 6” standard sphere) was suggested. A series of sensitivity studies indicated that (1) the spectral correction factors are quite universal and independent of the selection of the following three neutron calibration sources: 252Cf, 241Am and 239Pu; (2) the spectral correction factors for the following four neutron dosemeters (6”, 7”, 8”, and 9” Bonner spheres) are similar in trend; (3) the HEN-index can have several choices, e.g. the ratio of 4P6_8/6” or 3P5_7/5”, provided that the extended-range spheres are lead embedded and have the same thickness of polyethylene as that of the corresponding standard sphere. In the end of this study, similar spectral correction factors were established for the home-made Bonner cylinders, which, although not fully symmetric in geometry, exhibit an efficiency of about 20 times higher than that of the Bonner spheres.