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First $^{94}$Nb($n,γ$) Measurement: Constraining the Nucleosynthetic Origin of $^{94}$Mo in Presolar Grains

J. Balibrea-Correa, J. Lerendegui-Marco, C. Domingo-Pardo, V. Babiano-Suarez, I. Ladarescu, M. Krtivcka, G. Cescutti, S. Cristallo, D. Vescovi, N. Liu, E. A. Maugeri, U. Köster, I. M\önch, A. Casanovas, V. Alcayne, D. Cano-Ott, E. Mendoza, O. Aberle, J. Andrzejewski, S. Altieri, S. Amaducci, M. Bacak, C. Beltrami, S. Bennett, A. P. Bernardes, E. Berthoumieux, R. Beyer, M. Boromiza, D. Bosnar, M. Caamaño, F. Calviño, M. Calviani, D. M. Castelluccio, F. Cerutti, S. Chasapoglou, E. Chiaveri, P. Colombetti, N. Colonna, P. Console Camprini, G. Cortés, M. A. Cortés-Giraldo, L. Cosentino, S. F. Dellmann, M. Diakaki, M. Di Castro, M. Dietz, S. Di Maria, R. Dressler, E. Dupont, I. Durán, Z. Eleme, S. Fargier, B. Fernández, B. Fernández-Domínguez, P. Finocchiaro, S. Fiore, V. Furman, F. García-Infantes, A. Gawlik-Ramikega, G. Gervino, S. Gilardoni, E. González-Romero, C. Guerrero, F. Gunsing, C. Gustavino, J. Heyse, W. Hillman, D. G. Jenkins, E. Jericha, A. Junghans, Y. Kadi, K. Kaperoni, G. Kaur, A. Kimura, I. Knapová, M. Kokkoris, Y. Kopatch, N. Kyritsis, C. Lederer-Woods, G. Lerner, A. Manna, T. Martínez, A. Masi, C. Massimi, P. Mastinu, M. Mastromarco, A. Mazzone, A. Mengoni, V. Michalopoulou, P. M. Milazzo, R. Mucciola, F. Murtas, E. Musacchio González, A. Musumarra, A. Negret, N. Patronis, J. A. Pavón, M. G. Pellegriti, P. Pérez-Maroto, A. Pérez de Rada Fiol, J. Perkowski, C. Petrone, E. Pirovano, J. Plaza del Olmo, S. Pomp, I. Porras, J. Praena, J. M. Quesada, R. Reifarth, D. Rochman, Y. Romanets, C. Rubbia, A. Sánchez-Caballero, M. Sabaté-Gilarte, P. Schillebeeckx, D. Schumann, A. Sekhar, A. G. Smith, N. V. Sosnin, M. E. Stamati, A. Sturniolo, G. Tagliente, A. Tarifeñoo-Saldivia, D. Tarrío, P. Torres-Sánchez, S. Urlass, E. Vagena, S. Valenta, V. Variale, P. Vaz, G. Vecchio, V. Vlachoudis, R. Vlastou, A. Wallner, P. J. Woods, T. Wright, R. Zarrella, P. Zugec, The n\_TOF Collaboration

Abstract

Isotopic measurements of presolar silicon carbide grains from dying stars have revealed a puzzling overabundance of $^{94}$Mo that stellar nucleosynthesis models have failed to reproduce for two decades. This discrepancy challenged our understanding of the slow neutron-capture process ($s$-process) that forges approximately half of the elements heavier than iron. The key uncertainty lies at $^{94}$Nb, a radiactive branching point where competition between neutron capture and beta decay governs the $^{94}$Mo production, yet the neutron-capture cross section had never been measured. Here we report the first experimental determination of the $^{94}$Nb(n,$γ$)$^{95}$Nb cross section important for Mo isotopic abundances. The measurement was enabled by a coordinated effort involving high-purity target preparation at Institute of Solid State and Materials Research (IFW) Dresden, radioactive sample production at the Institut Laue-Langevin (ILL) Grenoble, radiochemical characterization at Paul Scherrer Institute (PSI) Villigen, and the Time-of-Flight CERN n$\_$TOF facility using for the first time segmented total-energy detectors. Incorporation of the resulting Maxwellian-averaged cross section into fully coupled nucleosynthesis models of low-mass asymptotic giant branch (AGB) stars brings them into agreement with the presolar grain data. These results remove a major nuclear-physics input uncertainty at the $^{94}$Nb branching point and provide a firmer foundation for understanding the origin of $^{94}$Mo in the solar system.

First $^{94}$Nb($n,γ$) Measurement: Constraining the Nucleosynthetic Origin of $^{94}$Mo in Presolar Grains

Abstract

Isotopic measurements of presolar silicon carbide grains from dying stars have revealed a puzzling overabundance of Mo that stellar nucleosynthesis models have failed to reproduce for two decades. This discrepancy challenged our understanding of the slow neutron-capture process (-process) that forges approximately half of the elements heavier than iron. The key uncertainty lies at Nb, a radiactive branching point where competition between neutron capture and beta decay governs the Mo production, yet the neutron-capture cross section had never been measured. Here we report the first experimental determination of the Nb(n,)Nb cross section important for Mo isotopic abundances. The measurement was enabled by a coordinated effort involving high-purity target preparation at Institute of Solid State and Materials Research (IFW) Dresden, radioactive sample production at the Institut Laue-Langevin (ILL) Grenoble, radiochemical characterization at Paul Scherrer Institute (PSI) Villigen, and the Time-of-Flight CERN nTOF facility using for the first time segmented total-energy detectors. Incorporation of the resulting Maxwellian-averaged cross section into fully coupled nucleosynthesis models of low-mass asymptotic giant branch (AGB) stars brings them into agreement with the presolar grain data. These results remove a major nuclear-physics input uncertainty at the Nb branching point and provide a firmer foundation for understanding the origin of Mo in the solar system.
Paper Structure (1 equation, 4 figures)

This paper contains 1 equation, 4 figures.

Figures (4)

  • Figure 1: The s-process path along the Zr-Nb-Mo region,i.e $^{93}$Zr and $^{94}$Nb. In the figure is highlighted the $^{94}$Nb branching point.
  • Figure 2: MACS as a function of $kT$ obtained from experimental data, compared with purely KADoNiS estimation. See text for details.
  • Figure 3: Molybdenum three-isotope plot comparing MS, Y, and Z grains with the $2~M_{\odot}$ magnetic fruity models predictions utilizing the MACS measured in this work. The grain data are ploted with 1 $\sigma$ uncertaintiesLiu19Stephan19Stephan25. The lines with symbols trace the trajectory of envelope isotopic compositions at two different metallicities ($Z$), with symbols indicating phases where the envelope becomes C-rich ($C/O>$1), a necessary condition for SiC dust condensation. The $Z_{\odot}$ adopted in the models is 0.0185.
  • Figure 4: Time-evolution of the key Zr, Nb, and Mo isotopes and the neutron density (dashed gray line) during a representative thermal pulse for the $2~M_{\odot}$ obtained from magnetic fruity models.