#n_TOF #paper #publishedShedding Light on the Origin of 204Pb, the Heaviest 𝑠-Process–Only Isotope in the Solar System
A. Casanovas-Hoste et al. (n_TOF Collaboration)
Phys. Rev. Lett. 133, 052702
https://doi.org/10.1103/PhysRevLett.133.052702(OA)
Shedding Light on the Origin of $^{204}\mathrm{Pb}$, the Heaviest $s$-Process--Only Isotope in the Solar System
Asymptotic giant branch stars are responsible for the production of most of the heavy isotopes beyond Sr observed in the solar system. Among them, isotopes shielded from the $r$-process contribution by their stable isobars are defined as $s$-only nuclei. For a long time the abundance of $^{204}\mathrm{Pb}$, the heaviest $s$-only isotope, has been a topic of debate because state-of-the-art stellar models appeared to systematically underestimate its solar abundance. Besides the impact of uncertainties from stellar models and galactic chemical evolution simulations, this discrepancy was further obscured by rather divergent theoretical estimates for the neutron capture cross section of its radioactive precursor in the neutron-capture flow, $^{204}\mathrm{Tl}$ (${t}_{1/2}=3.78\text{ }\text{ }\mathrm{yr}$), and by the lack of experimental data on this reaction. We present the first ever neutron capture measurement on $^{204}\mathrm{Tl}$, conducted at the CERN neutron time-of-flight facility n_TOF, employing a sample of only 9 mg of $^{204}\mathrm{Tl}$ produced at the Institute Laue Langevin high flux reactor. By complementing our new results with semiempirical calculations we obtained, at the $s$-process temperatures of $kT\ensuremath{\approx}8\text{ }\text{ }\mathrm{keV}$ and $kT\ensuremath{\approx}30\text{ }\text{ }\mathrm{keV}$, Maxwellian-averaged cross sections (MACS) of 580(168) mb and 260(90) mb, respectively. These figures are about 3% lower and 20% higher than the corresponding values widely used in astrophysical calculations, which were based only on theoretical calculations. By using the new $^{204}\mathrm{Tl}$ MACS, the uncertainty arising from the $^{204}\mathrm{Tl}(\mathrm{n},\ensuremath{\gamma})$ cross section on the $s$-process abundance of $^{204}\mathrm{Pb}$ has been reduced from $\ensuremath{\sim}30%$ down to $+8%/\ensuremath{-}6%$, and the $s$-process calculations are in agreement with the latest solar system abundance of $^{204}\mathrm{Pb}$ reported by K. Lodders in 2021.
#n_TOF #paper #published
Measurement of the 140Ce(n,𝛾) Cross Section at n_TOF and Its Astrophysical Implications for the Chemical Evolution of the Universe
S. Amaducci et al. (n_TOF Collaboration)
Phys. Rev. Lett. 132, 122701
https://doi.org/10.1103/PhysRevLett.132.122701
(open access)
Measurement of the $^{140}\mathrm{Ce}(\mathrm{n},\ensuremath{\gamma})$ Cross Section at n_TOF and Its Astrophysical Implications for the Chemical Evolution of the Universe
A widening gap between the cerium-140 abundance predicted by theories and that measured in observations of certain stars indicates a potential need for updated models of element formation.
The n_TOF Nuclear Physics Winter School 2024
The n_TOF Nuclear Physics Winter School 2024 is meant to cover some of the most significant topics related to nuclear science and applications. The School is specially addressed to n_TOF PhD students and young post-docs, but it is open to anyone interested in the fields covered. Four general topics are covered by the lectures: nuclear structure nuclear reactions nuclear astrophysics nuclear technologies Additional related topics are treated in specific lectures (see the Timetable).
#n_TOF paper published:
Measurement of the 14N(n,p)14C cross section at the CERN n_TOF facility from subthermal energy to 800 keV
Pablo Torres-Sánchez et al. (The n_TOF Collaboration )
Phys. Rev. C 107, 064617
#NuclearAstrophysics
https://doi.org/10.1103/PhysRevC.107.064617
Measurement of the $^{14}\mathrm{N}(n,p)^{14}\mathrm{C}$ cross section at the CERN n_TOF facility from subthermal energy to 800 keV
Background: The $^{14}\mathrm{N}(n,p)^{14}\mathrm{C}$ reaction is of interest in neutron capture therapy, where nitrogen-related dose is the main component due to low-energy neutrons, and in astrophysics, where $^{14}\mathrm{N}$ acts as a neutron poison in the $s$ process. Several discrepancies remain between the existing data obtained in partial energy ranges: thermal energy, keV region, and resonance region.Purpose: We aim to measure the $^{14}\mathrm{N}(n,p)^{14}\mathrm{C}$ cross section from thermal to the resonance region in a single measurement for the first time, including characterization of the first resonances, and provide calculations of Maxwellian averaged cross sections (MACS).Method: We apply the time-of-flight technique at Experimental Area 2 (EAR-2) of the neutron time-of-flight (n_TOF) facility at CERN. $^{10}\mathrm{B}(\mathrm{n},\ensuremath{\alpha})^{7}\mathrm{Li}$ and $^{235}\mathrm{U}(n,f)$ reactions are used as references. Two detection systems are run simultaneously, one on beam and another off beam. Resonances are described with the $R$-matrix code sammy.Results: The cross section was measured from subthermal energy to 800 keV, resolving the first two resonances (at 492.7 and 644 keV). A thermal cross section was obtained ($1.809\ifmmode\pm\else\textpm\fi{}0.045$ b) that is lower than the two most recent measurements by slightly more than one standard deviation, but in line with the ENDF/B-VIII.0 and JEFF-3.3 evaluations. A 1/$v$ energy dependence of the cross section was confirmed up to tens of keV neutron energy. The low energy tail of the first resonance at 492.7 keV is lower than suggested by evaluated values, while the overall resonance strength agrees with evaluations.Conclusions: Our measurement has allowed determination of the $^{14}\mathrm{N}(n,p)$ cross section over a wide energy range for the first time. We have obtained cross sections with high accuracy (2.5%) from subthermal energy to 800 keV and used these data to calculate the MACS for $kT=5$ to $kT=100$ keV.
Thomas Rauscher