Improvement of 93mNb and 103mRh activity measurement methodology for reactor dosimetry

Reactor dosimetry is based on the analysis of the activity of irradiated dosimeters, such as 93m Nb and 103m Rh. The activity measurement of these dosimeters is conventionally performed by X-ray spectrometry, but the low-energy of emitted photons makes it difficult to derive reliable results with low uncertainties. Approaches to improve these characterisations are presented: they include high accuracy efficiency calibration of a HPGe detector using both experiments and Monte Carlo simulation, calculation of corrective factors for the geometry (selfabsorption) and self-fluorescence effects. Improvement of the knowledge of the 103m Rh decay scheme is also required and a specific experiment is proposed, including activity measurement of a 103m Rh solution by liquid scintillation, and measurement of the photon emission intensities by X-ray spectrometry. A method for calculating coefficients to take into account the self-fluorescence effects in dosimeters is also suggested to improve the uncertainties on activity measurements.