Speaker
Description
Accurate neutron-capture cross sections are essential ingredients for improving stellar nucleosynthesis models and resolving discrepancies between predicted and observed isotopic abundances. In particular, the $^{94}$Nb(n,$\gamma$) reaction plays a key role in the s-process production of $^{94}$Mo in asymptotic giant branch (AGB) stars, where traditional models fail to reproduce the isotopic ratios observed in pre-solar grains [1]. However, no experimental data have been available so far for this reaction beyond thermal energies, mainly due to the challenges associated with producing high-quality radioactive samples and the count rate limitations of conventional detection systems.
To address this issue, the $^{94}$Nb(n,$\gamma$) cross section was measured in 2022 [2] at the CERN n_TOF facility EAR2 [3]. The experiment employed a hyper-pure $^{93}$Nb sample activated at the high-flux reactor of ILL-Grenoble, combined with a state-of-the-art detection setup based on an array of small Total-Energy Detectors, sTED, arranged in a compact ring configuration [4,5]. This setup, together with the high instantaneous neutron flux of EAR2, enabled a significant improvement in the signal-to-background ratio and sensitivity to the $^{94}$Nb capture signal. Additional C$_{6}$D$_{6}$ and LaCl$_{3}$(Ce) detectors were used to control systematic effects.
The experimental $^{94}$Nb(n,$\gamma$) cross section results in the neutron energy range from thermal up to 1 keV neutron energy will be presented, along with a discussion of their implications for s-process nucleosynthesis in the Mo region.
[1] M. Lugaro et al. APJ (2003) 486.
[2] J. Balibrea-Correa et al: EPJ Web Conf. 279 (2023) 06004
[3] C. Weiss et al., NIM-A 799, 90-98 (2015)
[4] V. Alcayne et al., Radiat.Phys.Chem. 217 (2024) 111525
[5] J. Balibrea-Correa et al: Nucl.Instrum.Meth.A 1064 (2024) 169385