Study of the 12C(p,g)13N at astrophysical energies at LUNA

abstract: The 12C/13C ratio is a sensitive indicator of the degree of stellar nucleosynthesis and thus it can be used as a tracer of galactic chemical evolution. Nevertheless, the C isotopic ratio variation after the dredge-up phenomenons occuring in Asymptotic Giant Branch (AGB) and Red Giant Branch (RGB) stars is highly dependant on the adopted rate for the proton capture reaction on 12 C. In a RGB star, the Gamow peak of the reaction lies between 20 and 70 keV. Given the exponential drop of the cross section, the reactions at such low energies are very difficult to measure because of the very low signal counting rate. Nevertheless, a precise measurement of the 12C(p, γ)13N reaction magnitude is necessary to make reliable predictions about the evolution of RGB stars. On the contrary, the Gamow peak for an AGB stars lies between 50 and 150 keV. This energy range can be measured through the detection of prompt γ-rays. Measurements of the 12C(p,γ)13N reaction cross section were performed at the Laboratory for Underground Nuclear Astrophysics (LUNA), located at the Labaratori Nazionali del Gran Sasso (LNGS) in Italy. Being located underground, the γ-ray background is suppressed by more than three orders of magnitude, thus providing a unique environment for low-energy measurements of reaction cross sections. Prompt γ-rays associated with the formation of 13 N nuclei were analysed to determine the non-resonant contribution to the reaction cross section. The total non-resonant S-factor was determined at energies between E cm ≈ 75 − 350 keV, obtained with great precision. Nevertheless, the preliminary results are discordant with the literature data. The reason of such a discrepancy is still unkown and has to be understood in future analysis

Use of jet-charge algorithms in the study of Bs -> JPsiPhi decay at CMS experiment

La misura della violazione della simmetria CP nel decadimento del mesone Bs nel canale JPsiPhi consente di osservare l'eventuale presenza di segnali di nuova fisica oltre il modello standard delle interazioni elettrodeboli. All'esperimento CMS tale decadimento puo' essere studiato mediante un'analisi delle distribuzioni angolari dei prodotti del decadimento della JPsi in due muoni e della Phi in due kaoni. La sensibilita` dell'analisi e' maggiore quando e' possibile determinare il "sapore" del mesone inizialmente prodotto, Bso anti-Bs; questo puo' essere inferito dalla prodotti di decadimento di un secondo adrone contenente un quark "b" nello stesso evento, tra i quali puo' pure essere presente un muone. Alternativamente puo' essere determinata una carica media, opportunamente pesata, delle particelle riconducibili al decadimento di un secondo quark "b". La determinazione della possibilita' di determinare il "sapore" del mesone al momento della produzione in base all'analisi delle particelle prodotte nel decadimento di un secondo adrone con "b" costituisce pure un elemento essenziale in questa misura

Measurement and analysis techniques for a study of

The 12C(p,γ) and 13C(p,γ) reaction cross sections are currently under investigation in the low-background environment of the Laboratory for Underground Nuclear Astrophysics. Both reactions are being studied using different types of solid targets, and employing complementary detection techniques (HPGe spectroscopy, total absorption spectroscopy and activation counting). To reduce systematic uncertainties, targets must be accurately characterized and their degradation monitored under the intense (~ 400 µA) beam of the LUNA400 accelerator. We present the experimental techniques employed, and the analyses developed for the study of these reactions

Low-energy Cross Section Measurements of

The 12C(p, γ)13N reaction cross section is currently under investigation in the low-background environment of the Laboratory for Underground Nuclear Astrophysics (LUNA). It is being studied using different types of solid targets, and employing two complementary detection techniques: HPGe spectroscopy and activation counting. To reduce systematic uncertainties, targets have been accurately characterized and their degradation under the intense beam of the LUNA-400 accelerator monitored. We present the experimental techniques and the corresponding analyses used to extract the reaction cross section

Growth model and structure evolution of Ag layers deposited on Ge films

We investigated the crystallinity and optical parameters of silver layers of 10–35 nm thickness as a function 2–10 nm thick Ge wetting films deposited on SiO2 substrates. X-ray reflectometry (XRR) and X-ray diffraction (XRD) measurements proved that segregation of germanium into the surface of the silver film is a result of the gradient growth of silver crystals. The free energy of Ge atoms is reduced by their migration from boundaries of larger grains at the Ag/SiO2 interface to boundaries of smaller grains near the Ag surface. Annealing at different temperatures and various durations allowed for a controlled distribution of crystal dimensions, thus influencing the segregation rate. Furthermore, using ellipsometric and optical transmission measurements we determined the time-dependent evolution of the film structure. If stored under ambient conditions for the first week after deposition, the changes in the transmission spectra are smaller than the measurement accuracy. Over the course of the following three weeks, the segregation-induced effects result in considerably modified transmission spectra. Two months after deposition, the slope of the silver layer density profile derived from the XRR spectra was found to be inverted due to the completed segregation process, and the optical transmission spectra increased uniformly due to the roughened surfaces, corrosion of silver and ongoing recrystallization. The Raman spectra of the Ge wetted Ag films were measured immediately after deposition and ten days later and demonstrated that the Ge atoms at the Ag grain boundaries form clusters of a few atoms where the Ge–Ge bonds are still present

First measurement of the low-energy direct capture in Ne 20 (p,¿) Na 21 and improved energy and strength of the Ec.m.=368 keV resonance

The 20Ne(p,¿)21Na reaction is the slowest in the NeNa cycle and directly affects the abundances of the Ne and Na isotopes in a variety of astrophysical sites. Here we report the measurement of its direct capture contribution, for the first time below Ec.m.=352 keV, and of the contribution from the Ec.m.=368 keV resonance, which dominates the reaction rate at T=0.03–1.00 GK. The experiment was performed deep underground at the Laboratory for Underground Nuclear Astrophysics, using a high-intensity proton beam and a windowless neon gas target. Prompt ¿ rays from the reaction were detected with two high-purity germanium detectors. We obtain a resonance strength ¿¿=(0.112±0.002stat±0.005sys)meV, with an uncertainty a factor of 3 smaller than previous values. Our revised reaction rate is 20% lower than previously adopted at T<0.1 GK and agrees with previous estimates at temperatures T=0.1 GK. Initial astrophysical implications are presented.Postprint (published version

Recent results and future perspectives with solid targets at LUNA

The stellar evolution and chemical make-up of the Universe are determined by nuclear reactions occurring in a wide variety of stellar sites. Precise determinations of the cross sections of these reactions are crucial for the calculation of reaction rates and for the development of stellar evolution models. The Laboratory for Underground Nuclear Astrophysics (LUNA) collaboration has been at the forefront of the direct measurement of nuclear reactions at the low energies of astrophysical interest for the last 35 years. The many signi cant results achieved at LUNA have been made possible due to the low background conditions uniquely available thanks to its location deep underground at the Laboratori Nazionali del Gran Sasso. Another key aspect of these successes is due to the experience of the LUNA collaboration in the production and characterization of a variety of solid targets used in reaction measurements. In this review, the main production techniques of solid targets are described, as well as the common methods adopted for target degradation monitoring. We also present the results of recent measurements using these targets and the future plans of the LUNA collaboration for measurements using solid targets at the LUNA400 kV and the new Ion Beam Facility (IBF) 3.5 MV are also presented

Towards automatic coupling corrections with DOROS BPMs (MD750)

BPMs close to IP1 and IP5 have been equipped with the new DOROS (Diode ORbit OScillation) system which provides precise orbit and turn-by-turn data [1]. In this MD-note we report on the rst measurements with the DOROS system to measure the transverse coupling. Furthermore, we compare the results and the performance of the system to the normal BPMs

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