Fast neutron dose rate monitoring using off the shelf Helium-4 scintillation detectors
The capability to measure neutron dose rate with an accuracy of +/- 20% is demonstrated for the helium-4 fast neutron scintillation detector model s670 by Arktis Radiation Detectors. Measurements were performed utilizing quasi-monoenergetic neutron fluxes in an energy range between 0.144 and 14.8 MeV as well as using calibrated Cf-252 and Americium-Beryllium (Am-Be) sources.
The elastic scattering reaction between neutrons and (_^4)He enables detection of neutrons whilst preserving the information about their energy. This measurement technique does not require neutron moderators, resulting in a remarkably lighter configuration. The readings from the detector were plotted against neutron energy to obtain energy calibration curves. Neutron fluence rates measured by certified laboratory detectors were used to calculate intrinsic efficiency values for various irradiation energies.
Fluence per unit dose equivalent factors were used to derive the ambient dose equivalent rate values from the measured neutron energy spectra. The results are used to implement a dose rate calculation in the system software, capable of providing neutron ambient dose equivalent rate values. The accuracy of the computed values is validated with calibrated Cf-252 and Am-Be sources. This work highlights the versatility of such a system, which extends to applications where not only simple neutron counting is required but neutron energy information is also of interest to assess the radiological risk caused by a neutron flux. This system can be used in a variety of applications ranging from dose monitoring in nuclear power plants to risk-assessment of nuclear waste drums coming from the decommissioning of nuclear facilities.
Keywords: neutron; safety; helium-4; dose