A New Neutron Dosimetry System at Soreq Nuclear Research Center

A new Landauer® neutron dosimetry system was recently installed in the External Dosimetry Laboratory (EDL) of the Radiation Safety Division at Soreq Nuclear Research Center (SNRC). The system permits dosimetry for two types of neutron dosimeters: a fast neutron dosimeter and a dosimeter for a combination of fast, intermediate, and thermal neutrons. The dosimeters are made of poly-allyl diglycol carbonate (PADC), also known as CR-39.

CR-39 dosimeters can measure H_p(10) doses for thermal neutrons in the range 0.10 mSv - 20 mSv and for intermediate and fast neutrons (40 keV to 14 MeV) in the range 0.10 mSv - 250 mSv, showing linear response for these dose ranges.

The dosimetry workflow in the EDL is hereby described: the CR-39 dosimeters are first immersed into an etching bath which contains a 5.5 mol/L NaOH solution warmed to 74° C for 15.5 hours. The CR-39 sensitive areas are then read using an automatically fed Zeiss microscope coupled to a CCD camera. For each CR-39, the microscope captures 15 different images of the fast neutrons region and 3 images of the thermal neutrons region. A detection software of tracks then analyzes these images. Track detection is based on morphological criteria. For double check, dosimeters the doses of which are found above the EDL reporting threshold by the analysis software are systematically reviewed manually.

The new system is presently undergoing a process of validation in order to meet the requirements for ISO/IEC 17025, so the EDL at SNRC will be able to provide a neutron dosimetry service accredited by the Israeli Laboratory Accreditation Authority.

Additionally to the neutron dosimetry service, the EDL plans to perform some research activities using the new system, such as heavy ion interaction studies, space dosimetry studies and cross section studies. The possibility of discriminating energies of neutrons by their dosimetric properties will also be investigated.