Development of new reference beams for calibration and control of radiation protection dosimeters
In recent years, the LNHB has initiated and carried out a research program to produce a reference radiation field for the calibration and control of high energy (several MeV) radiation protection dosimeters from its medical linear accelerator (LINAC).
For this purpose, a combination of a target and filter (flattening filter-attenuator) has been designed by the LNHB to produce a reference photon beam from the electron beam delivered by the LINAC, meeting the requirements of ISO 4037-1 standard. The main objective of this work was to provide secondary calibration laboratories with traceability to a national reference in the field of high energies. The average energy in terms of fluence of the radiation field thus created is approximately 7 MeV, with average dose equivalent rates compatible with the requirements of radiation protection. Passive dosimeters and ionization chambers are calibrated in this radiation beam, dosimeters based on scintillators and proportional counters cannot be calibrated due to the high instantaneous dose equivalent rate per radiation pulse. The transfer of the reference to a more suitable facility is currently under study to overcome this difficulty.
The scarcity of radioactive source producers (irradiator type using 60Co and 137Cs) and the increasing regulatory constraints linked to their possession led the laboratory to question the medium-term sustainability of this type of radiation source in order to make dosimetric references.
A study is currently under way to examine the possibility of producing reference photon beams from an electron accelerator, characterized in terms of dose equivalent in the energy range comparable to 60Co or 137Cs and capable of replacing these sources.