22 research outputs found
nuclear astrophysics deep underground
Cross sections of nuclear reactions relevant for astrophysics are crucial ingredients to understand the energy generation inside stars and the synthesis of the elements. At astrophysical energies, nuclear cross sections are often too small to be measured in laboratories on the Earth surface, where the signal would be overwhelmed by the cosmic-ray induced background. LUNA is a unique Nuclear Astrophysics experiment located at Gran Sasso National Laboratories. The extremely low background achieved at LUNA allows to measure nuclear cross sections directly at the energies of astrophysical interest. Over the years, many crucial reactions involved in stellar hydrogen burning as well as Big Bang nucleosynthesis have been measured at LUNA. The present contribution provides an overview on underground Nuclear Astrophysics as well as the latest results and future perspectives of the LUNA experiment
Low-energy resonances in the 22Ne(p,γ)23Na reaction directly observed at LUNA
The 22Ne(p,γ)23Na reaction is involved in the hydrogen burning neon-sodium (NeNa) cycle. This cycle is active in asymptotic giant branch stars (AGB) as well as in novae. In the Gamow window temperature range (30MK < T < 420 MK corresponding to proton center of mass energies 40 keV < E < 430 keV), the 22Ne(p,γ)23Na reaction rate is highly uncertain because of the contribution of a large number of resonances never measured directly. A study of this reaction has been carried out at the Laboratory for Underground Nuclear Astrophysics (LUNA), in the Gran Sasso National Laboratory, using a windowless gas target and two high-purity germanium detectors. Several resonances have been observed for the first time in a direct experiment
Strengths of the resonances at 436, 479, 639, 661, and 1279 keV in the Ne(p,)Na reaction
The Ne(p,)Na reaction is included in the neon-sodium
cycle of hydrogen burning. A number of narrow resonances in the Gamow window
dominates the thermonuclear reaction rate. Several resonance strengths are only
poorly known. As a result, the Ne(p,)Na thermonuclear
reaction rate is the most uncertain rate of the cycle. Here, a new experimental
study of the strengths of the resonances at 436, 479, 639, 661, and 1279 keV
proton beam energy is reported. The data have been obtained using a tantalum
target implanted with Ne. The strengths of the resonances
at 436, 639, and 661 keV have been determined with a relative approach, using
the 479 and 1279 keV resonances for normalization. Subsequently, the ratio of
resonance strengths of the 479 and 1279 keV resonances was determined,
improving the precision of these two standards. The new data are consistent
with, but more precise than, the literature with the exception of the resonance
at 661 keV, which is found to be less intense by one order of magnitude. In
addition, improved branching ratios have been determined for the gamma decay of
the resonances at 436, 479, and 639 keV.Comment: Final version, now using the Kelly et al. (2015) data [15] for
normalization; 10 pages, 7 figures, 3 table
Underground Measurements of Nuclear Reaction Cross-Sections Relevant to AGB Stars
none14noneAnanna, Chemseddine; Barile, Francesco; Boeltzig, Axel; Bruno, Carlo Giulio; Cavanna, Francesca; Ciani, Giovanni Francesco; Compagnucci, Alessandro; Csedreki, Laszlo; Depalo, Rosanna; Ferraro, Federico; Masha, Eliana; Piatti, Denise; Rapagnani, David; Skowronski, JakubAnanna, Chemseddine; Barile, Francesco; Boeltzig, Axel; Bruno, Carlo Giulio; Cavanna, Francesca; Ciani, Giovanni Francesco; Compagnucci, Alessandro; Csedreki, Laszlo; Depalo, Rosanna; Ferraro, Federico; Masha, Eliana; Piatti, Denise; Rapagnani, David; Skowronski, Jaku
New direct measurement of the 10 B(p,α) 7 Be reaction with the activation technique
Boron plays an important role in astrophysics and, together with lithium and beryllium, is a probe of stellar structure during the pre-main sequence and main-sequence phases. In this context, the 10 B(p, α ) 7 Be reaction is of particular interest.The literature data show discrepancies in the energy range between 100 keV and 2 MeV. This also poses a normalization problem for indirect data obtained with the Trojan Horse Method.A new measurement of the 10 B(p, α ) 7 Be reaction cross section was performed at Legnaro National Laboratories (LNL). At LNL, the cross section was determined with the activation technique by measuring the activated samples at a low-background counting facility. The analysis of that experiment is now complete and the results are here presented
22Ne and 23Na ejecta from intermediate-mass stars: The impact of the new LUNA rate for 22Ne(p,gamma)23Na
We investigate the impact of the new LUNA rate for the nuclear reaction NeNa on the chemical ejecta of intermediate-mass stars, with particular focus on the thermally-pulsing asymptotic giant branch (TP-AGB) stars that experience hot-bottom burning. To this aim we use the PARSEC and COLIBRI codes to compute the complete evolution, from the pre-main sequence up to the termination of the TP-AGB phase, of a set of stellar models with initial masses in the range , and metallicities , , and . We find that the new LUNA measures have much reduced the nuclear uncertainties of the Ne and Na AGB ejecta, which drop from factors of to only a factor of few for the lowest metallicity models. Relying on the most recent estimations for the destruction rate of Na, the uncertainties that still affect the Ne and Na AGB ejecta are mainly dominated by evolutionary aspects (efficiency of mass-loss, third dredge-up, convection). Finally, we discuss how the LUNA results impact on the hypothesis that invokes massive AGB stars as the main agents of the observed O-Na anti-correlation in Galactic globular clusters. We derive quantitative indications on the efficiencies of key physical processes (mass loss, third dredge-up, sodium destruction) in order to simultaneously reproduce both the Na-rich, O-poor extreme of the anti-correlation, and the observational constraints on the CNO abundance. Results for the corresponding chemical ejecta are made publicly available
The 10B(p,α)7Be S(E)-factor from 5 keV to 1.5 MeV using the Trojan Horse Method
The 10 B(p, α ) 7 Be reaction is the main responsible for the 10 B destruction in stellar interior [1]. In such environments this p-capture process occurs at a Gamow energy of 10 keV and takes places mainly through a resonant state (Ex = 8.701 MeV) of the compound 11 C nucleus. Thus a resonance right in the region of the Gamow peak is expected to significantly influence the behavior of the astrophysical S(E)-factor. The 10 B(p, α ) 7 Be reaction was studied via the Trojan Horse Method (THM) applied to the 2 H( 10 B, α 7 Be)n in order to extract the astrophysical S(E)-factor in a wide energy range from 5 keV to 1.5 MeV
New direct measurement of the 10
Boron plays an important role in astrophysics and, together with lithium and beryllium, is a probe of stellar structure during the pre-main sequence and main-sequence phases. In this context, the 10B(p,α)7 Be reaction is of particular interest.
The literature data show discrepancies in the energy range between 100 keV and 2 MeV. This also poses a normalization problem for indirect data obtained with the Trojan Horse Method.
A new measurement of the 10B(p,α)7 Be reaction cross section was performed at Legnaro National Laboratories (LNL). At LNL, the cross section was determined with the activation technique by measuring the activated samples at a low-background counting facility. The analysis of that experiment is now complete and the results are here presented