1,721,055 research outputs found
The Study of the Li-6(p,gamma)Be-7 Reaction at LUNA
No full textThe Li-6(p,gamma)Be-7 reaction is mainly involved in two astrophysical scenarios: the primordial nucleosynthesis and Li-6 consumption in pre-main and main sequence stars. A recent measurement of Li-6(p,gamma)Be-7 reaction S-factor reported a resonance-like structure at E-cm = 195 keV, which has not been confirmed neither by other direct measurements nor by theoretical calculations.A new experiment was performed at the Laboratory for Underground Nuclear Astrophysics (LUNA). The extremely low background environment allowed to measure the Li-6(p,gamma)Be-7 cross section down to low energies with unprecedented sensitivity leading to clarify the existence of the claimed resonance. Details on the experimental setup and the preliminary results of the ongoing analysis are reported in this work
The Study of the Ne(α,γ)Mg Reaction at LUNA
No full textThe Ne(α,γ)Mg reaction is the competitor of the Ne(α,n) Mg reaction, an effective neutron source for element synthesis through s-process. Currently the ratio between the rates of these two reactions is affected by high uncertainty because of the wide range of values proposed for the Ne(α,γ)_{-15}^{−9} eV). The present study represents the first direct measurement. This was performed at the ultra-low background LUNA laboratory where an high efficiency detector was installed at the gas target beamline of LUNA 400kV accelerator. The Ne gas, 99% enriched in Ne, was irradiated with a 399.9 keV α-beam. No significant signal was detected in the 22 Ne(α,γ)Mg region of interest, thus an upper limit for the 395 keV resonance strength was estimated
Underground measurement at LUNA found no evidence for a low-energy resonance in the
Full text linkThe 6Li(p,γ)7Be reaction is involved in all three main nucleosynthesis scenarios: Big Bang Nucleosynthesis, the interaction of cosmic rays with interstellar matter, and stellar nucleosynthesis.
Conflicting experimental results have been reported in literature for the 6Li(p,γ)7Be reaction cross section trend at astrophysical energies. A recent direct measurement found a resonance-like structure at Ec.m. = 195 keV, corresponding to an excited state at Ex ~ 5800 keV in 7Be which, however, has not been confirmed by either theoretical calculations or other direct measurements. In order to clarify the existence of this resonance, a new experiment was performed at the Laboratory for Underground Nuclear Astrophysics, located deep underground at Laboratori Nazionali del Gran Sasso (Italy). The 6Li(p,γ)7Be cross section was measured in the energy range Ec.m. = 60-350 keV with unprecedented sensitivity and no evidence for the alleged resonance was found
The Study of the Li(p, ) Be Reaction at LUNA
No full textThe Li(p) Be reaction is of interest in many different astrophysical scenarios, as for example the early stages of the star evolution. Recently a resonant structure was observed at E = 195 keV but it is still not confirmed by both theoretical and experimental studies. In order to investigate the existence of the resonance and to constrain the Li(p) Be S-factor at low energies a direct measurement was performed at LUNA. A High Purity Germanium was used in close geometry. A Silicon detector was inserted in backward geometry in order to detect the particles by Li(p) He reaction. Five solid targets were irradiated from E = 80 keV up to E = 390 keV and the ongoing analysis suggests there are no resonances
LUNA measurement found no evidence of a low-energy resonance in
No full textThe 6Li(p, γ)7Be reaction is mainly at work in three nucleosynthesis scenarios: Big Bang Nucleosynthesis, 6Li depletion in pre-main and in main sequence stars and cosmic ray interaction with interstellar matter. The 6Li(p, γ)7Be S-factor trend was poorly constrained at astrophysical energies because of conflicting experimental results reported in literature. A recent direct measurement, indeed, found a resonance-like structure at Ec.m. = 195 keV, corresponding to an excited state at Ex ∼ 5800 keV in 7Be which, however, has not been confirmed by either other direct measurements or predicted by theoretical calculations.
In order to clarify the existence of this resonance, a new experiment was performed at the Laboratory for Underground Nuclear Astrophysics (LUNA), located deep underground in Gran Sasso Laboratory. Thanks to the extremely low background environment, the 6Li(p, γ)7Be cross section was measured in the center-of-mass energy range E = 60-350 keV with unprecedented sensitivity.
No evidence for the alleged resonance was found. LUNA results was confirmed by latest published indirect determination of 6Li(p, γ)7Be S-factor and it is supported by a recent theoretical study
Towards a direct measurement of the Ecm= 65 keV resonance strength in 17O(p, γ)18F at LUNA
Full text linkThe 17O(p, γ)18F reaction plays a crucial role in several stellar scenarios where the hydrogen burning phases takes place. In particular, in the temperature energy range of interest for AGB nucleosynthesis (20 MK< T <80 MK) the main contribution to the astrophysical reaction rate comes from the elusive 65 keV resonance. Indeed, this resonance strength is at the moment determined only through indirect measurements, with a reported value of ωγ = (1.6 ± 0.3) × 10-11 eV. With typical experimental quantities for beam current, isotopic enrichment and detection efficiency, this strength yields an expected count rate of less than one count per Coulomb, making the direct measurement of this resonance extremely challenging. The Laboratory for Underground Nuclear Astrophysics (LUNA) 400kV accelerator installed in Laboratori Nazionali del Gran Sasso (Italy) provides a unique possibility to directly measure this low resonance thanks to the reduction of cosmic ray background by six orders of magnitude with respect surface laboratories and thanks to an intense, narrow proton beam. To improve the experimental sensitivity, the environmental background was further reduced designing a lead and borated (5%) polyethylene shielding and the absorption of γ - rays emitted by the reaction was minimised by the installation of target chamber and holder made of aluminum. With about 400 Coulomb accumulated on Ta2O5 targets, with nominal 17O enrichment of 90%, the LUNA collaboration has performed the first direct measurement of the 65 keV resonance strength
Towards a direct measurement of the
No full textThe 17O(p, γ)18F reaction plays a crucial role in the hydrogen burning phases of different stellar scenarios. At temperature of interest for AGB nucleosynthesis (20 MK < T < 80 MK) the main contribution to the astrophysical reaction rate comes from the poorly constrained 65 keV resonance. The strength of this resonance is presently determined only through indirect measurements, with a reported value of ωγ = (1.6 ± 0.3) 10−11 eV. With typical experimental quantities for beam current, isotopic enrichment and detection efficiency, this strength yields to an expected count rate of less than one count per Coulomb, making the direct measurement of this resonance extremely challenging.
A new high sensitivity setup has been installed at LUNA (Laboratory for Underground Nuclear Astrophysics) of Laboratori Nazionali del Gran Sasso. The high performance LUNA 400kV accelerator underground location guarantees, indeed, a reduction of cosmic ray background by several orders of magnitude. The residual background was further reduced by a devoted shielding of lead and borated (5%) polyethylene. On the other hand, the 4π BGO detector efficiency was optimized installing aluminum target chamber and holder. With about 400 C accumulated on Ta2O5 targets, with nominal 17O enrichment of 90%, the LUNA collaboration has performed the first direct measurement of the 65 keV resonance strength
Deuterium burning measurement at LUNA and its astrophysical and nuclear implications
Full text linkThe D(p,γ) 3He reaction is responsible for the deuterium destruction during the Big Bang Nucleosynthesis (BBN) and affects the primordial deuterium abundance. This latter is sensitive to fundamental cosmological parameters such as
the baryon density and the effective number of relativistic species. In this paper, we describe the most precise direct measurement of the D(p,γ) 3He reaction in the BBN energy range (Ecm = 30–280 keV) at the LUNA (Laboratory for Underground Nuclear Astrophysics) facility in Gran Sasso National Laboratories. Experimental results, cosmological consequences, and future prospects are reported here
Deuterium burning measurement at LUNA and its astrophysical and nuclear implications
Full text linkThe D(p,γ)3He reaction is responsible for the deuterium destruction during the Big Bang Nucleosynthesis (BBN) and affects the primordial deuterium abundance. This latter is sensitive to fundamental cosmological parameters such as the baryon density and the effective number of relativistic species. In this paper, we describe the most precise direct measurement of the D(p,γ)3He reaction in the BBN energy range (Ecm = 30-280 keV) at the LUNA (Laboratory for Underground Nuclear Astrophysics) facility in Gran Sasso National Laboratories. Experimental results, cosmological consequences, and future prospects are reported here
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