Spectral correction factors for conventional neutron dosemeters used in high-energy neutron environments

Abstract

High-energy neutrons (>10 MeV) contribute substantially to the dose fraction but result in only a small or negligible response in most conventional moderated-type neutron detectors. Neutron dosemeters used for radiation protection purpose are commonly calibrated with (252)Cf neutron sources and are used in various workplace. A workplace-specific correction factor is suggested. In this study, the effect of the neutron spectrum on the accuracy of dose measurements was investigated. A set of neutron spectra representing various neutron environments was selected to study the dose responses of a series of Bonner spheres, including standard and extended-range spheres. By comparing (252)Cf-calibrated dose responses with reference values based on fluence-to-dose conversion coefficients, this paper presents recommendations for neutron field characterisation and appropriate correction factors for responses of conventional neutron dosemeters used in environments with high-energy neutrons. The correction depends on the estimated percentage of high-energy neutrons in the spectrum or the ratio between the measured responses of two Bonner spheres (the 4P6_8 extended-range sphere versus the 6″ standard sphere).

Spectral Correction Factors for Conventional Neutron Dose Meters Used in High-Energy Neutron Environments—Improved and Extended Results Based on a Complete Survey of All Neutron Spectra in IAEA-TRS-403

“…Through a systematic study of this effect, the relationship between the neutron field characterization and the dose response of a 252 Cf-calibrated detector can be derived accordingly. Compared with our previous result (5) , the value of this work lies in providing an in-depth analysis of spectral correction factors based on a much larger database and sensitivity studies of key parameters. The result leads to a more rigorous and useful correction scheme than that previously provided.…”

“…In addition, standard Bonner spheres of diameters of 6", 7" and 8" were considered as alternative candidates of conventional type neutron dose meters in order to investigate the effect of various choices of neutron dose meters on the resulting correction factors. The response functions of Bonner spheres were calculated using the continuous-energy Monte calculations and validation, please refer to our previous papers (5,10) . Figure 1 shows the calculated response functions of five standard Bonner spheres of diameters ranging from 5" to 9" and two extended-range spheres 3P5_7 and 4P6_8.…”

“…Alternative spectral indices that replaces the flux percentage of high-energy neutrons have to be established. In our previous study (5) , the pair of an extended-range sphere 4P6_8 and a standard 6" sphere was selected for the purpose of constructing a spectral index, indicating the significance of high-energy neutrons in workplaces. The selection was based on an observation that the response functions of the 4P6_8 and 6" spheres are nearly overlap for low-energy neutrons and deviate substantially for neutron energies above 10 MeV (see Fig.1).…”

“…The phenomenon is well known to many health physics practitioners, especially those working at high-energy accelerator facilities. Improved detector designs, such as the so-called extended-range neutron dose meters, or suggested corrections for the responses of conventional neutron dose meters have been discussed in several studies (1)(2)(3)(4)(5) . For example, Klett et al.…”

“…In addition, Monte Carlo simulations were used to determine field specific correction factors for the 252 Cf-calibrated WEND-II, which resulted in a better agreement between calculations and measurements. In our previous study (5) , the effect of the neutron spectrum on the accuracy of dose measurements was systematically investigated by considering a set of ten selected neutron spectra representing various neutron environments. A simple correction scheme was provided for users to correct the dose underestimation of conventional neutron dose meters used in radiation fields with high-energy neutrons.…”