1,721,034 research outputs found
Neutron detection in nuclear astrophysics experiments: Study of organic liquid scintillators
No full textIn order to study the nuclear reaction 13 C(α,n)16 O, crucial for the nucleosynthesis of heavy nuclei (A>58), the LUNA collaboration at Laboratori Nazionali del Gran Sasso, is looking for the best neutron detector to use in the set up. One of the possibilities is to use detectors based on cell filled with Organic Liquid Scintillator BC501A. These detectors are sensible to fast neutron, but also to gamma rays. A Pulse Shape Discrimination process using the Zero Crossing method has been performed to select only signals from neutrons. Comparing the neutron spectra after the Pulse Shape Discrimination and the spectrum from a GEANT4 simulations, the efficiency of the BC501A, in function of the neutron energy and varying the light threshold, has been evaluated
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
Studying stars from the deep underground: the luna experiment and the case of
Full text linkUnderstanding the stellar evolution and the origin of chemical elements are the main goals of Nuclear Astrophysics. In the last century, many collaborations worked to develop experiments and accelerators to study in Earth laboratories the main nuclear processes taking place in stars at their relevant temperature. As an example, we present the measurement of the 13C(α,n)16O reaction performed by the LUNA collaboration
Direct Measurement of the 13 C(a,n)16O Reaction at LUNA
No full textThe13 C(a,n)16 reaction is the main neutron source for the s-process in low mass AGB stars. Although several direct measurements have been performed, no dataset reaches the Gamow window (140–230�keV) due to the the nearly exponential drop of (E) with decreasing energy. The available dataset didnâ€TMt extend to lower energies because of the strong cosmic background and some difficulties to evaluate the target degradation. To study the13 C(a,n)16 cross section at low energies, ancillary measurements to characterize13 C enriched evaporated targets, under an high intensity proton beam (100–200 A), are carried out at Laboratori Nazionali del Gran Sasso (LNGS) in the framework of the LUNA experiment. The preliminary results are reported in this contribution
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
The challenging direct measurement of the 65 keV resonance strength of the 17O(p,γ)18F reaction at LUNA
Full text linkA precise determination of proton capture rates on oxygen is mandatory to predict the abundance ratios of the oxygen isotopes in a stellar environment where hydrogen burning is active. The 17O(p,γ)18F reaction, specifically, plays a crucial role in AGB nucleosynthesis as well as in explosive hydrogen burning occurring in type Ia novae. At temperatures of interest for the former scenario (20 MK ≤ T ≤ 80 MK) the main contribution to the astrophysical reaction rate comes from the Ec.m. = 65 keV resonance. The strength of this resonance is presently determined only through indirect measurements, with an adopted value of ωγ = (1.6 ± 0.3) × 10−11 eV. Thanks to the low background environment of the Laboratori Nazionali del Gran Sasso, the intense and stable beam provided by the LUNA 400 kV accelerator and the experience in oxygen target production, the LUNA collaboration is aiming the first direct measurement of the above mentioned resonance strength. In the present work details of challenging direct measurement planned at LUNA will be described
Introduction of the new LUNA experimental setup for high precision measurement of the 13C(α,n)16O reaction for astrophysical purposes
No full textThe 13C(α,n)16O reaction is the prevalent neutron source for the main s-process. The direct measurement of this reaction at stellar temperature (kT=8 keV) has so far not been possible due to the very low cross section at the corresponding energy. The extrapolation of the astrophysical S-factor of this reaction into the Gamow window (Eα,c.m.=140-230 keV) is complicated by the large uncertainties of the low-energy experimental data and the existence of a state of 17O near the α-threshold that can have a large effect on low energy cross section. The aim of this paper is to introduce the new LUNA experimental setup, dedicated to the investigation of 13C(α,n)16O reaction below Eα,lab=400 keV
Direct Measurement of the (formula presented) Reaction at LUNA
No full textThe (formula presented) reaction is the main neutron source for the s-process in low mass AGB stars. Although several direct measurements have been performed, no dataset reaches the Gamow window (140–230 keV) due to the exponential drop of the cross section (formula presented)(E) with decreasing energy. The reaction rate becomes so low that the strong cosmic background would become predominant. In order to measure the (formula presented) cross section at low energies, ancillary measurements to understand the behaviour of 99% enriched (formula presented) evaporated targets, under a high intensity alpha beam (100–200 (formula presented)A). These measurements were carried out in deep underground laboratories of Laboratori Nazionali del Gran Sasso (LNGS) in the framework of the LUNA experiment. The preliminary results are reported in this contribution
Direct 13C(x,n)16O Cross Section Measurement at Low Energies
No full textThe reaction C,n O is the main neutron source in the “s process”, which is responsible for the production of about half of the heavy elements in the universe. It operates in thermally pulsing low mass AGB stars at temperatures of about 90 MK. This translates to a Gamow window between 140 and 230 keV, far below the Coulomb barrier. Various measurements of the low energy cross section of C,n O have been performed in the past, and while remarkable results have been achieved, ultimately the environmental background on the surface of the earth has been a limiting factor. The LUNA collaboration is currently performing a measurement of C,n O in the low-background environment of the LNGS, where the environmental neutron flux is reduced by over three magnitudes with respect to the surface. This unique location, together with a high-efficiency low background detector and state of the art electronics that allow suppression of the intrinsic background, has already enabled us to push the low-energy cross section limit beyond what has been reached before. Here we present the current status of the experiment, the plans for an upcoming next measurement campaign and preliminary results
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