Fri·Oct 3, 2025Friday·October 3, 2025

1. 01*

   High-spin spectroscopy and the onset of quasicollective structures in ${}^{69}$Ga

   F. E. Idoko · A. D. Ayangeakaa N. Sensharma · C. J. Chiara🇺🇸 · S. Zhu🇨🇳 · E. A. McCutchan · A. Saracino · R. V. F. Janssens🇺🇸 · H. M. Albers🇩🇪 · S. Balderrama · L. Canete🇫🇮 · J. Carroll🇺🇸 · M. P. Carpenter🇺🇸 and 21 other authors

   The intermediate- and high-spin level structure of the odd-$A$ ${}^{69}$Ga nucleus was investigated via the ${}^{26}$Mg(${}^{48}$Ca, $p4n\gamma$) fusion evaporation reaction at a beam energy of 195 MeV. The experiment was performed using the Gammasphere multidetector array in conjunction with the Fragment Mass Analyzer (FMA), with mass and charge identification achieved via an ionization chamber placed at the focal plane of the spectrometer. Coincidence relationships between the ${}^{69}$Ga reaction products and emitted $\gamma$ rays were analyzed to establish the level sequences, while angular distribution and angular correlation measurements were used to propose spin and parity assignments. As a result, the level scheme of the nucleus has been considerably extended. Near the ground state, the structure of ${}^{69}$Ga is well described by single-particle excitations, with shell-model calculations using the JUN45 and jj44b effective interactions providing a satisfactory interpretation of the observed levels. At spins in excess of 21/2 $\hslash$, three sequences of $E2$ transitions have been delineated, suggesting the onset of collectivity. An interpretation within the framework of the tilted-axis-cranking covariant density functional theory is proposed which reveals the role of $g_{9/2}$ protons and neutrons in this angular momentum regime.

   nucl-ex1 citation
2. 02*

   Study of the ${}^{20}$Ne($p,\gamma$)${}^{21}$Na reaction at LUNA

   A. Caciolli (on behalf of the LUNA collaboration)🇮🇹

   The NeNa-MgAl cycles are involved in the synthesis of Ne, Na, Mg, and Al isotopes. The ${}^{20}$Ne($p,\gamma$)${}^{21}$Na (Q = 2431.68 keV) reaction is the first and slowest reaction of the NeNa cycle and it controls the speed at which the entire cycle proceeds. At the state of the art, the uncertainty on the 20Ne(p,{\gamma})21Na reaction rate affects the production of the elements in the NeNa cycle. In particular, in the temperature range from 0.1 GK to 1 GK, the rate is dominated by the 366 keV resonance corresponding to the excited state of EX = 2797.5 keV and by the direct capture component. The present study focus on the study of the 366 keV resonance and the direct capture below 400 keV. At LUNA (Laboratory for Underground Nuclear Astrophysics) the ${}^{20}$Ne($p,\gamma$)${}^{21}$Na reaction has been measured using the intense proton beam delivered by the LUNA 400 kV accelerator and a windowless differential-pumping gas target. The products of the reaction are detected with two high-purity germanium detectors. The experimental details and preliminary results on the 366 keV resonance and on the direct capture component at very low energies will be shown, together with their possible impact on the ${}^{20}$Ne($p,\gamma$)${}^{21}$Na reaction rate.

   nucl-exEPJ Web Conf.(2024)·1 citation
3. 03*

   Status and future directions for direct cross-section measurements of the 13C(a,n)16O reaction for astrophysics

   L. Csedreki · Gy. Gyürky · D. Rapagnani · G.F. Ciani · M. Aliotta · C. Anannad · L. Barbieri · F. Barile · D. Bemmerer · A. Best · A. Boeltzig · C. Broggini and 36 other authors

   The 13C(a,n)16O reaction is the main neutron source of the s-process taking place in thermally pulsing AGB stars and it is one of the main candidate sources of neutrons for the i-process in the astrophysical sites proposed so far. Therefore, its rate is crucial to understand the production of the nuclei heavier than iron in the Universe. For the first time, the LUNA collaboration was able to measure the 13C(a,n)16O cross section at Ec.m.=0.23-0.3 MeV drastically reducing the uncertainty of the S(E)-factor in the astrophysically relevant energy range. In this paper, we provide details and critical thoughts about the LUNA measurement and compare them with the current understanding of the 13C(a,n)16O reaction in view of future prospect for higher energy measurements. The two very recent results (from the University of Notre Dame and the JUNA collaboration) published after the LUNA data represent an important step forward. There is, however, still room for a lot of improvement in the experimental study of the 13C(a,n)16O reaction, as emphasized in the present manuscript. We conclude that to provide significantly better constraints on the low-energy extrapolation, experimental data need to be provided over a wide energy range, which overlaps with the energy range of current measurements. Furthermore, future experiments need to focus on the proper target characterisation, the determination of neutron detection efficiency having more nuclear physics input, such as angular distribution of the 13C(a,n)16O reaction below Ea<0.8 MeV and study of nuclear properties of monoenergetic neutron sources and/or via the study of sharp resonances of 13C(a,n)16O. Moreover, comprehensive, multichannel R-matrix analysis with a proper estimate of uncertainty budget of experimental data are still required.

   nucl-exJ.Phys.G(2024)·2 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.