Personal dosimetry is of primordial importance for adequate protection of radiation workers. However, neutron dosimetry is still far less developed than photon dosimetry. This lack of precision is mainly caused by the fact that both the personal neutron dose and the dose assessed by a personal neutron dosimeter are strongly dependent on the neutron energy and angular distribution. It is very challenging to tune the personal neutron dosimeter response such that it provides an accurate assessment of the personal neutron dose for all possible neutron fields. For the moment, a factor of 2 difference from the reference is considered as acceptable. However, for most neutron dosimeters it is not possible to provide a response within a factor 2 from the reference for all possible neutron fields. Hence, in order to provide adequate protection of radiation workers, advancements in personal neutron dosimetry are required.
The goal of this PhD is to advance neutron dosimetry and thus to improve the protection of radiation workers in neutron workplace fields. This will be achieved by means of two complementary approaches.
1) The first approach is aimed at improving conventional personal neutron dosimetry with personal dosimeters by establishing and fully characterizing more realistic and flexible reference simulated neutron workplace fields. With flexible we mean that the simulated workplace field should be tuneable in terms of energy and angular distribution so that it can be adapted to match the real workplace fields. In the end this work will result in the availability of one or more facilities to calibrate personal neutron dosimeters more accurately for a wide range of possible neutron workplace fields. These facilities will be opened to the community on a service base.
2) The second approach is an innovative approach for personal neutron dosimetry using computational methods instead of a physical personal dosimeter. This method involves tracking of staff position and posture by means of 3D cameras and then by knowledge of the radiation field calculation of the personal dose in terms of Hp(10) or effective dose. Within this PhD the objective is to move computational neutron dosimetry to a level at which it can be used in practice. Within the European PODIUM project a limited feasibility study was performed. The neutron fields were characterized in detail by measurements and simulations to provide pre-calculated dose rate maps as input for the dose calculations. However, the methods for characterization used within PODIUM were very time-consuming. This is not realistic for application in real neutron workplace fields because the cost would be too high and often not all the necessary data will be available. Therefore, within this PhD it will be investigated how the field characterization can be made more efficient yet still sufficiently accurate for personal dosimetry. This will be done by the use of novel directional spectrometers, and simplified set-ups with personal dosimeters.
In the end the PhD will lead to significantly improved personal neutron dosimetry. For some workplace fields it will be possible to replace physical personal dosimeters with computational dosimetry. This computational dosimetry has the potential to be significantly more accurate than personal neutron dosimeters. However, in some complex and time dependent neutron workplace fields this approach might not be possible. Therefore, personal neutron dosimeters can probably never be completely avoided. But by establishing the flexible reference simulated neutron workplace fields also the accuracy of personal neutron dosimetry with personal dosimeters will be greatly enhanced.