Fluorescence correction for activity measurement of $^{93}$mNb in niobium dosimeters: calculation and experimental validation

Marie-Christine Lépy (1) , Jonathan Riffaud (1) , Christophe Domergue (2) , Herve Philibert (2) , Christophe Destouches (3) , Hubert Carcreff (4)

1 LNHB (CEA, LIST) - Laboratoire National Henri Becquerel (CEA, LIST)
2 LDCI - Laboratoire de Dosimétrie, de Contrôle-commande et Instrumentation
3 SPESI - Service Physique EXpérimentale, d'essais en Sûreté et d'Instrumentation
4 DM2S - Département de Modélisation des Systèmes et Structures

Niobium is a reference dosimeter for the survey of neutron damage to nuclear reactor vessels. Its characterization is based on the activity of $^{93}$mNb resulting from the $^{93}$Nb(n,n') activation reaction. The decay of $^{93}$mNb results mainly in the emission of niobium K X-rays which are used to determine the activity of $^{93}$mNb. Direct measurement using X-ray spectrometry does not require any sample preparation, but fluorescence effects, due to impurities which are activated during irradiation, must be taken into account. Indeed, some of these radioactive impurities, in particular $^{182}$Ta, and other niobium isotopes remain present during the measurements and disturb the X-ray spectra. The fluorescence effect induces an additional X-ray emission from niobium to that due only to the decay of $^{93}$mNb, leading to an overestimation of the dosimeter activity. It is therefore necessary to assess the contribution of fluorescence effects to provide accurate values of $^{93}$mNb activity. Fluorescence correction factors were established by Monte Carlo simulation. The calculated fluorescence correction factors were validated by an experimental approach, using activated niobium dosimeters with different tantalum concentrations

Keywords: radioactivity; ionizing radiation; dosimetry; neutrons; nuclear reactor; instrumentation; nuclear instrumentation; 93mNb; X-rays; Primary activity measurement; spectrometry; radioactive impurities; fluorescence effects; Monte Carlo; particle transport; simulation; modelling

Domains: Instrumentation and Detectors [physics.ins-det]; Nuclear Experiment [nucl-ex]

Marie-Christine Lépy, Jonathan Riffaud, Christophe Domergue, Herve Philibert, Christophe Destouches, et al.. Fluorescence correction for activity measurement of $^{93}$mNb in niobium dosimeters: calculation and experimental validation. 17th International Symposium on Reactor Dosimetry (ISRD 2023), May 2023, Lausanne, Switzerland. 01001 (9 p.), ⟨10.1051/epjconf/202327801001⟩. ⟨cea-04122563⟩