Neutron dosimetry

Introduction

In comparison to gamma dosimetry, neutron dosimetry is still far less established. For the moment no neutron personal dosemeter is available that measures the neutron personal dose equivalent within a 50% uncertainty level.

This lack of precision is mainly caused by the fact that the neutron dose is strongly energy and angular dependent. Moreover neutron energies in typical workplace fields vary with at least 10 orders of magnitude, demanding challenging requirements on neutron dosemeters and detectors.

Complete neutron field characterization in terms of energy and directional distribution is therefore indispensable for a reliable estimation of the neutron dose equivalent.

Main activities

  • Several measurement campaigns for neutron field characterization are being organised in several locations where the neutron dose can make a significant contribution to the occupationally received dose. Such locations can be found inside the containment structure of nuclear reactors and in the near environment of particle accelerators. Commercial devices are used for determination of the energy distribution and the total neutron fluence.
  • In case of a criticality accident, occupationally exposed workers can be the victim of severe neutron exposure. In such cases, specialized neutron dosimetry techniques are necessary, which differ markedly from those used in routine radiological protection. Therefore SCK•CEN has developed a system for criticality dosimetry based on activation detectors.

Applications

  • One of the most important applications of the research performed in neutron dosimetry is the establishment of local correction factors for neutron personal dosemeters. When neutron field characterization is performed in terms of energy and directional distribution, the neutron personal dose equivalent Hp(10) can be calculated. This allows us to compare the calculated value with the measured values by personal dosemeters and to propose site specific correction coefficients improving routine personal dosimetry.
  • Prepardness in the case of the event of a criticality accident. A big advantage of the current system based on activation detectors is that the neutron dosemeters do not require any maintenance or periodical read-out. Because criticality accidents occur, luckily, very rarely, therefore, a yearly test is performed in a well quantified neutron field in order to keep the knowledge and procedures up to date.

Projects

  • Neutron field characterization campaign in Tihange NPP.
  • The use of PIN-diodes in criticality dosimetry.

Contact

Filip Vanhavere

dosimetry@sckcen.be


Criticality dosemeter based on the activation detectors 197Au, 115In and 32S.