Thu·Oct 3, 2019Thursday·October 3, 2019

1. 01*

   First inverse kinematics measurement of key resonances in the ${}^{22}\text{Ne}(p,\gamma {)}^{23}\text{Na}$ reaction at stellar temperatures

   A. Lennarz🇨🇦 · M. Williams🇬🇧 · A. M. Laird🇬🇧 · U. Battino🇬🇧 · A. A. Chen🇿🇦 · D. Connolly · B. Davids🇨🇦 · N. Esker · R. Garg🇮🇳 · M. Gay · U. Greife🇺🇸 · U. Hager and 8 other authors

   In this Letter we report on the first inverse kinematics measurement of key resonances in the ${}^{22}\text{Ne}(p,\gamma {)}^{23}\text{Na}$ reaction which forms part of the NeNa cycle, and is relevant for ${}^{23}$Na synthesis in asymptotic giant branch (AGB) stars. An anti-correlation in O and Na abundances is seen across all well-studied globular clusters (GC), however, reaction-rate uncertainties limit the precision as to which stellar evolution models can reproduce the observed isotopic abundance patterns. Given the importance of GC observations in testing stellar evolution models and their dependence on NeNa reaction rates, it is critical that the nuclear physics uncertainties on the origin of ${}^{23}$Na be addressed. We present results of direct strengths measurements of four key resonances in ${}^{22}\text{Ne}(p,\gamma {)}^{23}\text{Na}$ at E${}_{\text{c}.m.}$ = 149 keV, 181 keV, 248 keV and 458 keV. The strength of the important E${}_{\text{c}.m.}$ = 458 keV reference resonance has been determined independently of other resonance strengths for the first time with an associated strength of $\omega \gamma$ = 0.439(22) eV and with higher precision than previously reported. Our result deviates from the two most recently published results obtained from normal kinematics measurements performed by the LENA and LUNA collaborations but is in agreement with earlier measurements. The impact of our rate on the Na-pocket formation in AGB stars and its relation to the O-Na anti-correlation was assessed via network calculations. Further, the effect on isotopic abundances in CO and ONe novae ejecta with respect to pre-solar grains was investigated.

   nucl-exPLB(2020)·12 citations
2. 02*

   A direct measurement of the 17O(a,g)21Ne reaction in inverse kinematics and its impact on heavy element production

   M.P. Taggart · C. Akers🇰🇷 · A.M. Laird🇬🇧 · U. Hager · C. Ruiz🇨🇦 · D.A. Hutcheon · M.A. Bentley · J.R. Brown🇬🇧 · L. Buchmann · A.A. Chen🇿🇦 · J. Chen🇺🇸 · K.A. Chipps🇺🇸 and 24 other authors

   During the slow neutron capture process in massive stars, reactions on light elements can both produce and absorb neutrons thereby influencing the final heavy element abundances. At low metallicities, the high neutron capture rate of 16-O can inhibit s-process nucleosynthesis unless the neutrons are recycled via the 17O(a,n)20Ne reaction. The efficiency of this neutron recycling is determined by competition between the 17O(a,n)20Ne and 17O(a,g)21Ne reactions. While some experimental data are available on the former reaction, no data exist for the radiative capture channel at the relevant astrophysical energies. The 17O(a,g)21Ne reaction has been studied directly using the DRAGON recoil separator at the TRIUMF Laboratory. The reaction cross section has been determined at energies between 0.6 and 1.6 MeV Ecm, reaching into the Gamow window for core helium burning for the first time. Resonance strengths for resonances at 0.63, 0.721, 0.81 and 1.122 MeV Ecm have been extracted. The experimentally based reaction rate calculated represents a lower limit, but suggests that significant s-process nucleosynthesis occurs in low metallicity massive stars.

   nucl-exPLB(2019)·8 citations
3. 03*

   9Li and 8He decays in GEANT4

   C.Jollet🇫🇷 · A.Meregaglia🇫🇷

   The decays of cosmogenic nuclei such as ${}^9$Li and ${}^8$He represent one of the largest irreducible backgrounds for reactor antineutrino experiments. The correct treatment of such decays are of fundamental importance in the study of cosmogenic backgrounds and in their rejection, hence the full chain of intermediate excited states must be accounted for. Currently the treatment in GEANT4 of the modelling of de-excitation of ${}^9$Be and ${}^8$Li, which are the daughter nuclei of ${}^9$Li and ${}^8$He respectively, is not correct. ${}^9$Be excited states should break into a neutron and two $\alpha$'s, and ${}^8$Li excited states should emit a neutron and possibly an $\alpha$ and a triton depending on the decay chain, whereas in GEANT4 they both reach the ground state by emitting a gamma. Based on the available nuclear measurements we included the correct treatment of ${}^9$Li and ${}^8$He decays in GEANT4 and compared the obtained results with the spectra published by the Double Chooz collaboration finding an excellent agreement.

   nucl-exhep-exNucl.Instrum.Meth.A(2020)·10 citations
4. 04*

   COHERENT Plans for D${}_2$O at the Spallation Neutron Source

   Rebecca Rapp (on behalf of the COHERENT collaboration)🇺🇸

   The Spallation Neutron Source (SNS) is a pulsed source of neutrons and, as a byproduct of this operation, an intense source of neutrinos via stopped-pion decay. The COHERENT collaboration uses this source to investigate coherent elastic neutrino-nucleus scattering (CEvNS) with a suite of detectors. To enable precise cross-section measurements, we must address an estimated 10\% uncertainty in our flux calculation associated with the lack of data for ${\pi }^{\pm }$ production from 1 GeV protons on an Hg target. We present here our Geant4 simulation of neutrino production at the SNS and our plans to experimentally normalize this flux with the development of a 670 kg D${}_2$O detector. Using the precise cross section calculations for neutrino interactions on deuterium, we will dramatically reduce our flux uncertainty.

   ↳ physics.ins-dethep-exnucl-ex3 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.