LUNA: Status and Prospects

The essential ingredients of nuclear astrophysics are the thermonuclear reactions which shape the life and death of stars and which are responsible for the synthesis of the chemical elements in the Universe. Deep underground in the Gran Sasso Laboratory the cross sections of the key reactions responsible for the hydrogen burning in stars have been measured with two accelerators of 50 and 400 kV voltage right down to the energies of astrophysical interest. As a matter of fact, the main advantage of the underground laboratory is the reduction of the background. Such a reduction has allowed, for the first time, to measure relevant cross sections at the Gamow energy. The qualifying features of underground nuclear astrophysics are exhaustively reviewed before discussing the current LUNA program which is mainly devoted to the study of the Big-Bang nucleosynthesis and of the synthesis of the light elements in AGB stars and classical novae. The main results obtained during the study of reactions relevant to the Sun are also reviewed and their influence on our understanding of the properties of the neutrino, of the Sun and of the Universe itself is discussed. Finally, the future of LUNA during the next decade is outlined. It will be mainly focused on the study of the nuclear burning stages after hydrogen burning: helium and carbon burning. All this will be accomplished thanks to a new 3.5 MV accelerator able to deliver high current beams of proton, helium and carbon which will start running under Gran Sasso in 2019. In particular, we will discuss the first phase of the scientific case of the 3.5 MV accelerator focused on the study of $^{12}$C+$^{12}$C and of the two reactions which generate free neutrons inside stars: $^{13}$C($\alpha$,n)$^{16}$O and $^{22}$Ne($\alpha$,n)$^{25}$Mg.Comment: To be published in Progress in Particle and Nuclear Physics 98C (2018) pp. 55-8

Positronium signature in organic liquid scintillators for neutrino experiments

Electron anti-neutrinos are commonly detected in liquid scintillator experiments via inverse beta decay, by looking at the coincidence between the reaction products, neutron and positron. Prior to positron annihilation, an electron-positron pair may form an orthopositronium (o-Ps) state, with a mean life of a few ns. Even if the o-Ps decay is speeded up by spin flip or pick off effects, it may introduce distortions in the photon emission time distribution, crucial for position reconstruction and pulse shape discrimination algorithms in anti-neutrino experiments. Reversing the problem, the o-Ps induced time distortion represents a new signature for tagging anti-neutrinos in liquid scintillator. In this paper, we report the results of measurements of the o-Ps formation probability and lifetime, for the most used solvents for organic liquid scintillators in neutrino physics (pseudocumene, linear alkyl benzene, phenylxylylethane, and dodecane). We characterize also a mixture of pseudocumene +1.5 g/l of 2,5-diphenyloxazole, a fluor acting as wavelength shifter. In the second part of the paper, we demonstrate that the o-Ps induced distortion of the scintillation photon emission time distributions represent an optimal signature for tagging positrons on an event by event basis, potentially enhancing the anti-neutrino detection.Comment: 6 pages, 9 figure

Primordial nucleosynthesis

Big Bang nucleosynthesis (BBN) describes the production of light nuclei in the early phases of the Universe. For this, precise knowledge of the cosmological parameters, such as the baryon density, as well as the cross section of the fusion reactions involved are needed. In general, the energies of interest for BBN are so low (E < 1MeV) that nuclear cross section measurements are practically unfeasible at the Earth’s surface. As of today, LUNA (Laboratory for Underground Nuclear Astrophysics) has been the only facility in the world available to perform direct measurements of small cross section in a very low background radiation. Owing to the background suppression provided by about 1400 meters of rock at the Laboratori Nazionali del Gran Sasso (LNGS), Italy, and to the high current offered by the LUNA accelerator, it has been possible to investigate cross sections at energies of interest for Big Bang nucleosynthesis using protons, 3He and alpha particles as projectiles. The main reaction studied in the past at LUNA is the 2H(4He, (Formula presented.))6Li. Its cross section was measured directly, for the first time, in the BBN energy range. Other processes like 2H(p, (Formula presented.))3He , 3He(2H, p)4He and 3He(4He, (Formula presented.))7Be were also studied at LUNA, thus enabling to reduce the uncertainty on the overall reaction rate and consequently on the determination of primordial abundances. The improvements on BBN due to the LUNA experimental data will be discussed and a perspective of future measurements will be outlined. © 2016, SIF, Springer-Verlag Berlin Heidelberg

Swelling of positronium confined in a small cavity

The electron density at the positron (contact density) in the ground state positronium (Ps) formed in condensed matter is generally found to be lower than in vacuum. This is usually attributed to microscopic electric fields which polarize Ps, by acting on the two particles of the atom. In this paper we quantitatively investigate an opposite effect. It is due to the confinement of Ps in small cavities existing in the host solid (e.g. free volume in polymers), which increases the contact density. Although this phenomenon is greater, the smaller is the size of the cavity, Ps polarization seems to play anyway a predominant role

Tracing U mobility in deep groundwater using Ra isotopes

The mobility of natural U is compared among four boreholes in a fractured granite using Ra isotopes and geochemical modelling. Rn-222/Ra-226 activity ratios (ARs) spanning an order of magnitude underline differences in reactive surface area. (Ra-224/Ra-228)(ARs) up to 9 indicate recent changes in hydrogeochemistry, and (Ra-226/Ra-228)(ARs) 0.6-30 indicate variable deposition of U. Dissolved U is related to dissolution of a solid U(VI) phase by groundwater with HCO3- > 20 mg.L-1. U reduction is hindered by Ca2UO2(CO3)(3)(0)

Herbicides inhibitors of EPSPs: literature review

Os herbicidas inibidores da enzima EPSPs, glyphosate e sulfosate, estão entre os produtos mais comercializados no Brasil e no mundo. Os objetivos dessa revisão de literatura são sintetizar informações quanto ao espectro de ação, características físico-químicas, princípios da absorção, translocação, metabolização, mecanismo de ação, comportamento ambiental e a resistência de plantas aos herbicidas inibidores de EPSPs. Com essa revisão, espera-se fornecer subsídios para que a comunidade agrícola possa utilizar esses compostos de forma mais racional, eficaz e econômica.The herbicides inhibitors ofthe enzyme EPSPs, glyphosate and sulfosate, are among the most used compounds in Brazil and in the world. The objectives ofthis review are to synthesize the information about the weeds controlled, physic-chemical characteristics, fundamentais of absorption, translocation, decomposition, mechanism of action, environmental performance, and plant resistance to the EPSPs inhibitors. With this review, we want to provide to the agricultural community information to obtain a more rational, efficient and economical performance ofthese compounds

Neutron-induced background by an alpha-beam incident on a deuterium gas target and its implications for the study of the 2H(alpha,gamma)6Li reaction at LUNA

The production of the stable isotope Li-6 in standard Big Bang nucleosynthesis has recently attracted much interest. Recent observations in metal-poor stars suggest that a cosmological Li-6 plateau may exist. If true, this plateau would come in addition to the well-known Spite plateau of Li-7 abundances and would point to a predominantly primordial origin of Li-6, contrary to the results of standard Big Bang nucleosynthesis calculations. Therefore, the nuclear physics underlying Big Bang Li-6 production must be revisited. The main production channel for Li-6 in the Big Bang is the 2H(alpha,gamma)6Li reaction. The present work reports on neutron-induced effects in a high-purity germanium detector that were encountered in a new study of this reaction. In the experiment, an {\alpha}-beam from the underground accelerator LUNA in Gran Sasso, Italy, and a windowless deuterium gas target are used. A low neutron flux is induced by energetic deuterons from elastic scattering and, subsequently, the 2H(d,n)3He reaction. Due to the ultra-low laboratory neutron background at LUNA, the effect of this weak flux of 2-3 MeV neutrons on well-shielded high-purity germanium detectors has been studied in detail. Data have been taken at 280 and 400 keV alpha-beam energy and for comparison also using an americium-beryllium neutron source.Comment: Submitted to EPJA; 13 pages, 8 figure

First Direct Measurement of the ^{17}O(p,\gamma)^{18}F Reaction Cross-Section at Gamow Energies for Classical Novae

Classical novae are important contributors to the abundances of key isotopes, such as the radioactive ^{18}F, whose observation by satellite missions could provide constraints on nucleosynthesis models in novae. The ^{17}O(p,\gamma)^{18}F reaction plays a critical role in the synthesis of both oxygen and fluorine isotopes but its reaction rate is not well determined because of the lack of experimental data at energies relevant to novae explosions. In this study, the reaction cross section has been measured directly for the first time in a wide energy range Ecm = 200 - 370 keV appropriate to hydrogen burning in classical novae. In addition, the E=183 keV resonance strength, \omega \gamma=1.67\pm0.12 \mueV, has been measured with the highest precision to date. The uncertainty on the ^{17}O(p,\gamma)^{18}F reaction rate has been reduced by a factor of 4, thus leading to firmer constraints on accurate models of novae nucleosynthesis.Comment: accepted by Phys. Rev. Let

Blood flow characteristics after aortic valve neocuspidization in paediatric patients: a comparison with the Ross procedure.

AIMS: The aortic valve (AV) neocuspidization (Ozaki procedure) is a novel surgical technique for AV disease that preserves the natural motion and cardiodynamics of the aortic root. In this study, we sought to evaluate, by 4D-flow magnetic resonance imaging, the aortic blood flow characteristics after AV neocuspidization in paediatric patients. METHODS AND RESULTS: Aortic root and ascending aorta haemodynamics were evaluated in a population of patients treated with the Ozaki procedure; results were compared with those of a group of patients operated with the Ross technique. Cardiovascular magnetic resonance studies were performed at 1.5 T using a 4D flow-sensitive sequence acquired with retrospective electrocardiogram-gating and respiratory navigator. Post-processing of 4D-flow analysis was performed to calculate flow eccentricity and wall shear stress. Twenty children were included in this study, 10 after Ozaki and 10 after Ross procedure. Median age at surgery was 10.7 years (range 3.9-16.5 years). No significant differences were observed in wall shear stress values measured at the level of the proximal ascending aorta between the two groups. The analysis of flow patterns showed no clear association between eccentric flow and the procedure performed. The Ozaki group showed just a slightly increased transvalvular maximum velocity. CONCLUSION: Proximal aorta flow dynamics of children treated with the Ozaki and the Ross procedure are comparable. Similarly to the Ross, Ozaki technique restores a physiological laminar flow pattern in the short-term follow-up, with the advantage of not inducing a bivalvular disease, although further studies are warranted to evaluate its long-term results