The Status and Future of Direct Nuclear Reaction Measurements for Stellar Burning

The study of stellar burning began just over 100 years ago. Nonetheless, we do not yet have a detailed picture of the nucleosynthesis within stars and how nucleosynthesis impacts stellar structure and the remnants of stellar evolution. Achieving this understanding will require precise direct measurements of the nuclear reactions involved. This report summarizes the status of direct measurements for stellar burning, focusing on developments of the last couple of decades, and offering a prospectus of near-future developments.Comment: Accepted to Journal of Physics G as a Major Report. Corresponding author: Zach Meisel ([email protected]

Improved astrophysical rate for the 18O(p,α)15N reaction by underground measurements

The 18O(p,\u3b1)15N reaction affects the synthesis of 15N, 18O and 19F isotopes, whose abundances can be used to probe the nucleosynthesis and mixing processes occurring deep inside asymptotic giant branch (AGB) stars. We performed a low-background direct measurement of the 18O(p,\u3b1)15N reaction cross-section at the Laboratory for Underground Nuclear Astrophysics (LUNA) from center of mass energy Ec.m.=340keV down to Ec.m.=55keV, the lowest energy measured to date corresponding to a cross-section of less than 1 picobarn/sr. The strength of a key resonance at center of mass energy Er=90keV was found to be a factor of 10 higher than previously reported. A multi-channel R-matrix analysis of our and other data available in the literature was performed. Over a wide temperature range, T=0.01\u20131.00GK, our new astrophysical rate is both more accurate and precise than recent evaluations. Stronger constraints can now be placed on the physical processes controlling nucleosynthesis in AGB stars with interesting consequences on the abundance of 18O in these stars and in stardust grains, specifically on the production sites of oxygen-rich Group II grains

A new study of 14N^{14}N(p,γ\gamma)15^{15}O at low energy

Die Reaktion $^{14}N$(p,$\gamma$)$^{15}$O ist die langsamste Kernreaktion des CNO-Zyklus und somit ein Schlüssel zum Verständnis verschiedener physikalischer Prozesse im Universum. Der solare CNO-Neutrinofluss z.B. ist linear vom Wirkungsquerschnitt dieser Reaktion abhängig. Die Reaktion ist auch von kosmologischer Bedeutung, da sie Einfluss auf die Bestimmung des Alters von Kugelsternhaufen hat. Diese sind die ältesten Objekte in unserer Galaxie und bilden daher eine Untergrenze für das Alter des Universums. Der Wirkungsquerschnitt der Reaktion $^{14}N$(p,$\gamma$)$^{15}$O wurde im Energiebereich $E_{p}$ = 140 bis 400 keV gemessen und die experimentellen Daten mit R-Matrix Rechnungen zu den relevanten Energien extrapoliert, deren Resultat einen astrophysikalischen S-Faktor von $S_{tot}$(0) = 1.7 $\pm 0.2$ keV b ergeben. Das Ergebnis ist etwa um einen Faktor 2 kleiner als der bisher akzeptierte Wert. Erste Modellrechnungen mit diesem neuen Resultat ergeben eine Erhöhung des Alters der Kugelsternhaufen um etwa 1 Milliarde Jahre

The nuclear physics of the hydrogen burning in the Sun

Underground nuclear astrophysics focuses its efforts towards a deeper knowledge of the nuclear reactions that rule stellar evolution processes and enable the synthesis of the elements of the periodic table. Deep underground in the Gran Sasso laboratory, the cross-sections of the key reactions of the hydrogen burning have been measured right down to the energies of astrophysical interest. The main results obtained by the LUNA Collaboration are reviewed, and their contributions to the solution of the solar neutrino problem and to the age of the globular cluster are discussed

Nuclei in the Cosmos XV (NIC XV)

These peer-reviewed NIC XV conference proceedings present the latest major advances in nuclear physics, astrophysics, astronomy, cosmochemistry and neutrino physics, which provide the necessary framework for a microscopic understanding of astrophysical processes. The book also discusses future directions and perspectives in the various fields of nuclear astrophysics research. In addition, it also includes a limited number of section of more general interest on double beta decay and dark matter

Final results on the

It is well established that the 13C(α, n)16O reaction (Q=2.215 MeV) is the major neutron source feeding the s-process in low mass (1−3M⊙) Asymptotic Giant Branch (AGB) stars. In the last decades, several measurements have been performed. Nevertheless, no dataset reaches the Gamow window (140 keV <Ec.m.<250 keV). This is due to the exponential drop of the cross section σ(E) with decreasing energy. The consequence is that the reaction rate becomes so low that the cosmic background becomes predominant in surface laboratories. A recent measurement was carried out in deep underground laboratory of Laboratori Nazionali del Gran Sasso (LNGS) in the framework of the LUNA experiment. To measure the 13C(α, n)16O cross section at low energies, a multiple effort has been performed to suppress the background in the setup, to maximise the detector efficiency and to keep under control the target modification under an intense stable beam provided by the LUNA accelerator (= 200 µA). Thanks to these accuracies, the 13C(α, n)16O cross section was measured in the center of mass energy range 230 keV <Ecm<305 keV with a maximum 20% overall uncertainty. This allowed to constrain the reaction rate at T=0.1 GK at 15% uncertainty and to lead the way for new possible astrophysical consequences

Enhanced electron screening in d(d,p)t for deuterated Ta*

The recent observation of a large electron screening effect in the d(d, p)t reaction using a deuterated Ta target has been confirmed using somewhat different experimental approaches: U-e = 309 +/- 12 eV for the electron screening potential energy. The high U, value arises from the environment of the deuterons in the Ta matrix, but a quantitative explanation is missing

Advances in radiative capture studies at LUNA with a segmented BGO detector

Studies of charged-particle reactions for low-energy nuclear astrophysics require high sensitivity, which can be achieved by means of detection setups with high efficiency and low backgrounds, to obtain precise measurements in the energy region of interest for stellar scenarios. High-efficiency total absorption spectroscopy is an established and powerful tool for studying radiative capture reactions, particularly if combined with the cosmic background reduction by several orders of magnitude obtained at the Laboratory for Underground Nuclear Astrophysics (LUNA). We present recent improvements in the detection setup with the Bismuth GermaniumOxide (BGO) detector at LUNA, aiming to reduce high-energy backgrounds and to increase the summing detection efficiency. The new design results in enhanced sensitivity of the BGO setup, as we demonstrate and discuss in the context of the first direct measurement of the 65 keV resonance (Ex = 5672 keV) of the 17O(p, γ)18F reaction. Moreover, we show two applications of the BGO detector, which exploit its segmentation. In case of complex γ-ray cascades, e. g. the de-excitation of Ex = 5672 keV in 18F, the BGO segmentation allows to identify and suppress the beam induced background signals that mimic the sum peak of interest. We demonstrate another new application for such a detector in form of in-situ activation measurementsof a reaction with β+ unstable product nuclei, e. g., the 14N(p, γ)15O reactio