Systematic study of the low-lying electric dipole strength in Sn isotopes and its astrophysical implications

The $\gamma$-ray strength functions (GSF) and nuclear level densities (NLD) below the neutron threshold have been extracted for $^{111-113,116-122,124}$Sn from particle-$\gamma$ coincidence data with the Oslo method. The evolution of bulk properties of the low-lying electric dipole response has been investigated on the basis of the Oslo GSF data and results of a recent systematic study of electric and magnetic dipole strengths in even-even Sn isotopes with relativistic Coulomb excitation. The obtained GSFs reveal a resonance-like peak on top of the tail of the isovector giant dipole resonance, centered at $\approx$8 MeV and exhausting $\approx$2\% of the classical Thomas-Reiche-Kuhn (TRK) sum. In contrast to predictions of the relativistic quasiparticle random-phase and time-blocking approximation calculations (RQRPA and RQTBA), no monotonous increase in the total low-lying $E1$ strength was observed in the experimental data from $^{111}$Sn to $^{124}$Sn, demonstrating rather similar strength distributions in these nuclei. The Oslo GSFs and NLDs were further used as inputs to constrain the cross sections and Maxwellian-averaged cross sections of $(n,\gamma)$ reactions in the Sn isotopic chain using TALYS. The obtained results agree well with other available experimental data and the recommended values from the JINA REACLIB, BRUSLIB, and KADoNiS libraries. Despite relatively small exhausted fractions of the TRK sum rule, the low-lying electric dipole strength makes a noticeable impact on the radiative neutron-capture cross sections in stable Sn isotopes. Moreover, the experimental Oslo inputs for the $^{121,123}$Sn$(n,\gamma)$$^{122,124}$Sn reactions were found to affect the production of Sb in the astrophysical $i$-process, providing new constraints on the uncertainties of the resulting chemical abundances from multi-zone low-metallicity Asymptotic Giant Branch stellar models.Comment: 27 pages, 14 pages. Submitted to Physical Review C journal on 13 November 202

Nuclear Level Density and γ\gamma-ray Strength Function of 67Ni^{67}\mathrm{Ni} and the impact on the i-process

Proton-$\gamma$ coincidences from $(\mathrm{d},\mathrm{p})$ reactions between a $^{66}\mathrm{Ni}$ beam and a deuterated polyethylene target have been analyzed with the inverse Oslo method to find the nuclear level density (NLD) and $\gamma$-ray strength function ($\gamma$SF) of $^{67}\mathrm{Ni}$. The $^{66}\mathrm{Ni}(\mathrm{n},\gamma)$ capture cross section has been calculated using the Hauser-Feshbach model in TALYS using the measured NLD and $\gamma$SF as constraints. We confirm that $^{66}\mathrm{Ni}(\mathrm{n},\gamma)$ acts as a bottleneck when relying on one-zone nucleosynthesis calculations. However, we find that the impact of this reaction is strongly damped in multi-zone low-metallicity AGB stellar models experiencing i-process nucleosynthesis.Comment: Submitted to Phys. Rev.

Context Sensitive Links Add to Marked List (0) Send to: Ions effects on sol-gel transition and rheological behavior in alumina slurries

International audienceAqueous slurries made of silica or alumina particles may behave like sols or like gels depending on the particle concentration, but also the pH or the ion force of the medium. The present study aimed at investigating the different sol-gel transitions observed in systems between a diluted state and concentrated formulations. For this purpose zeta potential and G', G '' measurements, reflecting elastic and viscous behaviors, were selected as the tools of choice to get insights into the mechanisms accounting for the sol-gel transition. We discuss about the relevancy of these simple measurements and affirm that they are sufficient to explain the evolutions in an alumina based system. Indeed, particles can adopt a "repulsive" organization at low salt concentration values (i.e. high surface potential values) or form an attractive percolating network, when the ion strength reaches a critical level. Moreover, the addition of NaOH can lead to very complex moduli variations as both the electrostatic shielding and the pH change; yet, these variations are easily predictable using our reasoning. (C) 2013 Elsevier B.V. All rights reserved