Neutron dosimetry is still far less developed than gamma dosimetry. At present there is no neutron personal dosimetry system available that measures with the same precision as photon dosemeters. Currently, a factor of 2 difference with the reference value is accepted. This lack of precision is mainly caused by the fact that the neutron dose is strongly depended on the neutron energy. A change in the neutron spectrum therefore leads to an important change in the neutron dose. Knowledge of the neutron spectrum is therefore indispensable for a good estimation of the neutron dose.
SCK•CEN is performing research to characterize the neutron fields in several situations and in several workplaces to be able to introduce a simple and accurate personal dosimetry system, based on an active dosimetry system, in mixed neutron/gamma fields to achieve adequate protection for radiological workers. SCK•CEN was a partner in the EVIDOS project, an international project for the Evaluation of Individual Dosimetry in Mixed neutron-gamma workplace fields. Within the EVIDOS project, all kinds of neutron personal and ambient dosemeters available were applied in real workplace fields and compared to well determined reference values, allowing the introduction of correction factors.
Although neutrons contribute not that much to the personal dose, the applications go from nuclear power plants, particle accelerators, space dosimetry to radiation therapy, where a specific number of workers can be exposed to non-negligible neutron doses.
Next to the development of a routine neutron dosimetry system, SCK•CEN has developed a system for neutron dosimetry in the case of a criticality accident among radiological workers. This system is based on the activation of gold foils, indium foils and sulphur tablets and is at the moment distributed among several partners. Criticality accidents occur, luckily, very rarely but the knowhow must be retained, therefore, every two years the system is tested with a well characterised reference dose.