Speaker
Description
The s-process is responsible for the synthesis of approximately half of the elements heavier than ⁵⁶Fe, and its nucleosynthesis yields in AGB and massive stars determine the isotopic abundances of heavy elements in the stellar systems. The most precise constraints available for the Nd isotopes are provided by isotopic ratio measurements from presolar stardust silicon carbide (SiC) grains. These observations are in persistent disagreement with stellar nucleosynthesis model predictions, which can be resolved if an enhancement of ~15% in the ¹⁴⁶Nd neutron capture cross section is assumed at the stellar temperature kT = 8 keV [1]. The existing experimental database for ¹⁴⁶Nd(n,γ) is severely limited: the reference data by Bao et al. [2] relies on a single measurement by Wisshak [3] restricted to the unresolved resonance region (URR) and in tension with other available data, while no time-of-flight measurement of the resolved resonance region (RRR) exists.
The s-process branching at ¹⁴⁷Nd is governed by the competition between neutron capture and β-decay, making the ¹⁴⁷Nd half-life a key nuclear input. A discrepancy exists in the literature between the long-standing reference value (10.98 d, Baba 1971 [4]) and a more recent measurement (11.26 d, Broderick 2019 [5]), with no consensus established. This uncertainty directly propagates into the predicted s-process isotopic ratios and limits the astrophysical interpretation of new cross section data.
To address these challenges, a comprehensive multi-facility experimental campaign has been undertaken combining time-of-flight and activation techniques. High-resolution TOF measurements at EAR2-n_TOF [6] provide, for the first time, resonance-resolved ¹⁴⁶Nd(n,γ) data up to ~5 keV and, possibly, the average neutron capture cross section in the URR up to 100 keV. Complementary neutron activation measurements at the HiSPANoS facility at CNA (Seville) [7], exploiting the well-characterised quasi-stellar kT = 25 keV spectrum from the ⁷Li(p,n) reaction, yield a direct MACS determination sensitive to the URR. A second activation campaign at the NEAR station at n_TOF [8], which provides access to the integral cross section in different energy ranges, completes the dataset. In parallel, a dedicated measurement of the ¹⁴⁷Nd half-life has been performed via neutron activation and HPGe γ-spectrometry.
This contribution presents preliminary results from this campaign, including the ¹⁴⁶Nd capture yield, the first experimental MACS values from activation, and a new ¹⁴⁷Nd half-life determination. The combined astrophysical impact on the s-process branching of ¹⁴⁷Nd and on the reconciliation with presolar SiC grain observations will be discussed.
[1] T. R. Ireland et al., Geochimica et Cosmochimica Acta 221, 200-218 (2018)
[2] Z.Y. Bao et al., Atomic Data Nucl. Data Tables 76, 70 (2000)
[3] K. Wisshak et al., Phys. Rev. C 57, 391 (1998)
[4] S. Baba et al., J. Inorg. Nucl. Chem. 33, 589 (1971)
[5] K. Broderick et al., Appl. Radiat. Isot. 144, 54 (2019)
[6] C. Weiss et al., Nucl. Inst. Methods A, 799, 90-98 (2015)
[7] M.A. Millán-Callado et al., Radiation Physics and Chemistry 217 (2024)
[8] N. Patronis et al., arXiv:2209.04443 (2022)