Neutron spectrometry with DIAMON detector for characterisation of a newly built neutron calibration facility at SCK CEN

Personal neutron dosimeters often experience significant overestimation or underestimation when used in neutron fields that differ from those in which they were calibrated. This discrepancy highlights the highly field-dependent nature of these dosimeters and the necessity for precise neutron field characterisation to ensure accurate calibration and reliable dosimetry. In this study, we conducted a comprehensive neutron field characterisation at the newly constructed neutron room of the Secondary Standard Dosimetry Laboratory (SSDL) of SCK CEN, Belgium, using 252Cf and 241Am-Be sources.
The DIAMON neutron spectrometer and Bonner Sphere Spectrometer (BSS) were employed, alongside Monte Carlo simulations. The primary objectives were to evaluate the performance of the DIAMON spectrometer against the BSS, which serve as the gold standard, and to validate the simulation model of the neutron room. The shadow cone method was utilised to separate direct and scattered neutron components. Monte Carlo simulations using the PHITS code, which mimicked the actual neutron room geometry, materials, and sources, were conducted to develop the neutron room model which is validated by the measurements. Analysis of neutron ambient dose equivalent rates from both sources, in terms of direct neutron under controlled scatter conditions (in this case, below 3 m), revealed that DIAMON measurements agreed with LNK reference values within a 16% margin. The deviations of BSS measurements and PHITS simulations from the LNK reference values were kept within 19% and 10%, respectively. These findings demonstrate the reliability of the DIAMON spectrometer and the robustness of the PHITS simulation model.