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

Abstract

Abstract. 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.

Improvement of the activity measurement method for solid dosimeters emitting X-rays

“…This section focuses on the additional fluorescence induced in niobium dosimeters (Riffaud et al, 2016b). As already mentioned, the (n,n′) reaction on Nb-93 is sensitive to fast neutrons with E > 1 MeV.…”

“…This work involved simulating the decay scheme for each radionuclide, taking into account the branching ratios, the electron and photon emission intensities and their interactions with the material and the atomic relaxation processes. The study (Riffaud et al, 2016b) gives a comprehensive description of the self-fluorescence coefficient calculation for each impurity based on spectra obtained through simulation for the niobium peaks.…”