The Study of 22Ne(a,g)26Mg and 6Li(p,g)7Be Reactions at LUNA

In the current work the study of the 22Ne(a,g)26Mg and of the 6Li(p,g)7 Be reactions are presented. Both reactions were investigated at LUNA, located under 1400 m of Gran Sasso rock (Italy). The rock coverage guarantees an unprecedented reduction of the cosmic rays background. The 22Ne(a,g)26Mg reaction plays a fundamental role in the nucleosynthesis of s- nuclei in low-mass AGB stars and in massive stars. Indeed, the 22Ne(a,g)26Mg reaction is the competitor of the 22Ne(a,n)25 Mg reaction, an effective neutron source for element synthesis through s-process. The ratio between the rates of these two reactions is crucial to estimate the impact of AGB stars and massive stars on the s-nuclei abundances. Currently this ratio is affected by high uncertainty because of the wide range of values proposed for the 22Ne(a,g)26Mg 395 keV resonance strength (10^(-15) - 10^(-9) eV). All the results reported in literature are derived from indirect measurements. The present study represents the first direct measurement to estimate the strength of the 395 keV resonance and its impact on the 22Ne(a,g)26Mg reaction rate. Because of the low resonance strength values an high efficiency detector was installed at the gas target beamline of LUNA400kV accelerator, where the Ne gas, 99% enriched in 22Ne, was irradiated with a 399.9 keV a-beam. No significant signal was detected in the 22Ne(a,g)26Mg region of interest, thus an upper limit for the 395 keV resonance strength was estimated. The 6Li is an important indicator of the stellar age and of mixing processes in stars. Indeed it is progressively depleted by stars during the pre-main and main sequence phase via both 6Li(p,g)7Be and 6Li(p,a)3He reaction. The 6Li(p,g)7Be reaction was studied by many groups but a recent work renewed the interest on this reaction. A resonance like structure was observed at Ecm ~ 195 keV (Ex ~ 5.8 MeV) which is neither predicted by theoretical studies nor seen in previous experiments. The new excited state could explain the angular distribution of the 6Li(p,a)3He reaction, which requires both negative and positive parity levels contribution. In addition, the new excited state may affect the Standard Big Bang Nucleosynthesis predictions and the extrapolation to low energy of the 3He(a,g)7Be cross section. The present work has the goal of investigating the existence of the 195 keV resonance and of measuring the 6Li(p,g)7Be cross section down to low energies to better constrain the S-factor extrapolation at energies of astrophysical interest. The measurement was performed at the solid target beamline of LUNA400kV accelerator, where a devoted scattering chamber was installed. Six targets of different composition and thickness were irradiated at energies between 80 keV and 390 keV. In addition to the HPGe detector, used to detect gamma-rays produced by the 6Li(p,g)7Be reaction, a Si detector was put in place to detect the charged particles produced by the 6Li(p,a)3He reaction. The results of this thesis do not confirm the resonance observed at Ecm ~ 195 keV

Underground Measurements of Nuclear Reaction Cross-Sections Relevant to AGB Stars

none14noneAnanna, Chemseddine; Barile, Francesco; Boeltzig, Axel; Bruno, Carlo Giulio; Cavanna, Francesca; Ciani, Giovanni Francesco; Compagnucci, Alessandro; Csedreki, Laszlo; Depalo, Rosanna; Ferraro, Federico; Masha, Eliana; Piatti, Denise; Rapagnani, David; Skowronski, JakubAnanna, Chemseddine; Barile, Francesco; Boeltzig, Axel; Bruno, Carlo Giulio; Cavanna, Francesca; Ciani, Giovanni Francesco; Compagnucci, Alessandro; Csedreki, Laszlo; Depalo, Rosanna; Ferraro, Federico; Masha, Eliana; Piatti, Denise; Rapagnani, David; Skowronski, Jaku

22Ne and 23Na ejecta from intermediate-mass stars: The impact of the new LUNA rate for 22Ne(p,gamma)23Na

We investigate the impact of the new LUNA rate for the nuclear reaction $^{22}$Ne$(p,\gamma)^{23}$Na on the chemical ejecta of intermediate-mass stars, with particular focus on the thermally-pulsing asymptotic giant branch (TP-AGB) stars that experience hot-bottom burning. To this aim we use the PARSEC and COLIBRI codes to compute the complete evolution, from the pre-main sequence up to the termination of the TP-AGB phase, of a set of stellar models with initial masses in the range $3.0\,M_{\odot} - 6.0\,M_{\odot}$, and metallicities $Z_{\rm i}=0.0005$, $Z_{\rm i}=0.006$, and $Z_{\rm i} = 0.014$. We find that the new LUNA measures have much reduced the nuclear uncertainties of the $^{22}$Ne and $^{23}$Na AGB ejecta, which drop from factors of $\simeq 10$ to only a factor of few for the lowest metallicity models. Relying on the most recent estimations for the destruction rate of $^{23}$Na, the uncertainties that still affect the $^{22}$Ne and $^{23}$Na AGB ejecta are mainly dominated by evolutionary aspects (efficiency of mass-loss, third dredge-up, convection). Finally, we discuss how the LUNA results impact on the hypothesis that invokes massive AGB stars as the main agents of the observed O-Na anti-correlation in Galactic globular clusters. We derive quantitative indications on the efficiencies of key physical processes (mass loss, third dredge-up, sodium destruction) in order to simultaneously reproduce both the Na-rich, O-poor extreme of the anti-correlation, and the observational constraints on the CNO abundance. Results for the corresponding chemical ejecta are made publicly available

Albiglutide and cardiovascular outcomes in patients with type 2 diabetes and cardiovascular disease (Harmony Outcomes): a double-blind, randomised placebo-controlled trial

Background: Glucagon-like peptide 1 receptor agonists differ in chemical structure, duration of action, and in their effects on clinical outcomes. The cardiovascular effects of once-weekly albiglutide in type 2 diabetes are unknown. We aimed to determine the safety and efficacy of albiglutide in preventing cardiovascular death, myocardial infarction, or stroke. Methods: We did a double-blind, randomised, placebo-controlled trial in 610 sites across 28 countries. We randomly assigned patients aged 40 years and older with type 2 diabetes and cardiovascular disease (at a 1:1 ratio) to groups that either received a subcutaneous injection of albiglutide (30–50 mg, based on glycaemic response and tolerability) or of a matched volume of placebo once a week, in addition to their standard care. Investigators used an interactive voice or web response system to obtain treatment assignment, and patients and all study investigators were masked to their treatment allocation. We hypothesised that albiglutide would be non-inferior to placebo for the primary outcome of the first occurrence of cardiovascular death, myocardial infarction, or stroke, which was assessed in the intention-to-treat population. If non-inferiority was confirmed by an upper limit of the 95% CI for a hazard ratio of less than 1·30, closed testing for superiority was prespecified. This study is registered with ClinicalTrials.gov, number NCT02465515. Findings: Patients were screened between July 1, 2015, and Nov 24, 2016. 10 793 patients were screened and 9463 participants were enrolled and randomly assigned to groups: 4731 patients were assigned to receive albiglutide and 4732 patients to receive placebo. On Nov 8, 2017, it was determined that 611 primary endpoints and a median follow-up of at least 1·5 years had accrued, and participants returned for a final visit and discontinuation from study treatment; the last patient visit was on March 12, 2018. These 9463 patients, the intention-to-treat population, were evaluated for a median duration of 1·6 years and were assessed for the primary outcome. The primary composite outcome occurred in 338 (7%) of 4731 patients at an incidence rate of 4·6 events per 100 person-years in the albiglutide group and in 428 (9%) of 4732 patients at an incidence rate of 5·9 events per 100 person-years in the placebo group (hazard ratio 0·78, 95% CI 0·68–0·90), which indicated that albiglutide was superior to placebo (p<0·0001 for non-inferiority; p=0·0006 for superiority). The incidence of acute pancreatitis (ten patients in the albiglutide group and seven patients in the placebo group), pancreatic cancer (six patients in the albiglutide group and five patients in the placebo group), medullary thyroid carcinoma (zero patients in both groups), and other serious adverse events did not differ between the two groups. There were three (<1%) deaths in the placebo group that were assessed by investigators, who were masked to study drug assignment, to be treatment-related and two (<1%) deaths in the albiglutide group. Interpretation: In patients with type 2 diabetes and cardiovascular disease, albiglutide was superior to placebo with respect to major adverse cardiovascular events. Evidence-based glucagon-like peptide 1 receptor agonists should therefore be considered as part of a comprehensive strategy to reduce the risk of cardiovascular events in patients with type 2 diabetes. Funding: GlaxoSmithKline

The Study of 22Ne(a,g)26Mg and 6Li(p,g)7Be Reactions at LUNA

In the current work the study of the 22Ne(a,g)26Mg and of the 6Li(p,g)7 Be reactions are presented. Both reactions were investigated at LUNA, located under 1400 m of Gran Sasso rock (Italy). The rock coverage guarantees an unprecedented reduction of the cosmic rays background. The 22Ne(a,g)26Mg reaction plays a fundamental role in the nucleosynthesis of s- nuclei in low-mass AGB stars and in massive stars. Indeed, the 22Ne(a,g)26Mg reaction is the competitor of the 22Ne(a,n)25 Mg reaction, an effective neutron source for element synthesis through s-process. The ratio between the rates of these two reactions is crucial to estimate the impact of AGB stars and massive stars on the s-nuclei abundances. Currently this ratio is affected by high uncertainty because of the wide range of values proposed for the 22Ne(a,g)26Mg 395 keV resonance strength (10^(-15) - 10^(-9) eV). All the results reported in literature are derived from indirect measurements. The present study represents the first direct measurement to estimate the strength of the 395 keV resonance and its impact on the 22Ne(a,g)26Mg reaction rate. Because of the low resonance strength values an high efficiency detector was installed at the gas target beamline of LUNA400kV accelerator, where the Ne gas, 99% enriched in 22Ne, was irradiated with a 399.9 keV a-beam. No significant signal was detected in the 22Ne(a,g)26Mg region of interest, thus an upper limit for the 395 keV resonance strength was estimated. The 6Li is an important indicator of the stellar age and of mixing processes in stars. Indeed it is progressively depleted by stars during the pre-main and main sequence phase via both 6Li(p,g)7Be and 6Li(p,a)3He reaction. The 6Li(p,g)7Be reaction was studied by many groups but a recent work renewed the interest on this reaction. A resonance like structure was observed at Ecm ~ 195 keV (Ex ~ 5.8 MeV) which is neither predicted by theoretical studies nor seen in previous experiments. The new excited state could explain the angular distribution of the 6Li(p,a)3He reaction, which requires both negative and positive parity levels contribution. In addition, the new excited state may affect the Standard Big Bang Nucleosynthesis predictions and the extrapolation to low energy of the 3He(a,g)7Be cross section. The present work has the goal of investigating the existence of the 195 keV resonance and of measuring the 6Li(p,g)7Be cross section down to low energies to better constrain the S-factor extrapolation at energies of astrophysical interest. The measurement was performed at the solid target beamline of LUNA400kV accelerator, where a devoted scattering chamber was installed. Six targets of different composition and thickness were irradiated at energies between 80 keV and 390 keV. In addition to the HPGe detector, used to detect gamma-rays produced by the 6Li(p,g)7Be reaction, a Si detector was put in place to detect the charged particles produced by the 6Li(p,a)3He reaction. The results of this thesis do not confirm the resonance observed at Ecm ~ 195 keV.Nella presente tesi sono presentati gli studi sperimentali delle reazioni 22Ne(a,g)26Mg e 6Li(p,g)7Be. Entrambe le reazioni sono state studiate a LUNA, che si trova sotto 1400 m di roccia del Gran Sasso, per aver un'efficiente schermatura dal fondo creato dai raggi cosmici. La reazione 22Ne(a,g)26Mg ha un ruolo fondamentale per la nucleosintesi dei nuclei tramite il processo s in stelle AGB di piccola massa e nelle stelle massicce. Infatti essa compete con la reazione 22Ne(a,n)25Mg, un’efficiente sorgente di neutroni per il processo s. Il rapporto tra i rates di queste due reazioni è una quantità cruciale per stimare l’impatto delle stelle AGB e delle stelle massicce sulle abbondanze dei nuclei s. Attualmente questo rapporto non è noto con accuratezza poiché il contributo della risonanza a 395 keV della reazione 22Ne(a,g)26Mg è ancora incerto. Tutti i risultati di intensità riportati in letteratura per questa risonanza sono stati dedotti da misure indirette. Il presente lavoro si propone di studiare il contributo della risonanza a 395 keV sul rate della 22Ne(a,g)26Mg con una misura diretta. Poichè i valori di inten- sità per la risonanza stanno tra 10^(-15) eV e 10^(-9) eV un rivelatore ad alta efficienza è stato installato sulla linea gassosa collegata all’acceleratore LUNA400kV. Il gas Neon, arricchito al 99% in 22Ne, è sato irradiato con un fascio di particelle a con un energia di 399.9 keV. Nessun segnale significativo è stato rilevato nella regione energetica dello spettro di interesse per la reazione 22Ne(a,g)26Mg, perciò è stato calcolato un limite superiore per l'intensità della risonanza a 395 keV. Il 6Li è un importante indicatore dell'età stellare e dei processi di mescolamento nelle stelle. Infatti esso viene progressivamente distrutto dalle stelle nella fase precedente e durante la sequenza principale via le reazioni 6Li(p,a)3He e 6Li(p,g)7Be. La reazione 6Li(p,g)7Be è stata studiata da molti gruppi e un recente esperimento ha riacceso l’interesse per questa reazione. Una risonanza è stata osservata a Ecm ~ 195 keV (Ex ~ 5.8 MeV), né prevista da studi teorici né osservata in precedenti esperimenti. Il nuovo stato eccitato potrebbe però spiegare la distribuzione angolare della reazione 6Li(p,a)3He, che richiede il contributo sia di livelli con parità positiva e negativa. Inoltre, il nuovo stato eccitato potrebbe avere un effetto sulle predizioni della Standard Big Bang Nucleosynthesis e sull’estrapolazione a bassa energia della sezione d’urto della reazione 3 He(a,g)7Be. Lo studio attuale ha lo scopo di investigare l’esistenza della risonanza a 195 keV e di misurare la sezione d’urto della reazione 6Li(p,g)7Be fino a basse energie così da meglio estrapolare il fattore astrofisico, S(E), a energie di interesse astrofisico. La misura è stata svolta usando la linea solida dell’acceleratore LUNA400kV dove una camera di scattering dedicata è stata montata. Sei bersagli di diversa composizione e spessore sono stati irradiati a energie tra 80 keV e 390 keV. Assieme al rivelatore gamma HPGe, un silicio è stato usato per rivelare le particelle cariche prodotte dalla reazione 6Li(p,a)3He. I risultati di questa tesi non confermano la risonanza a Ecm ~ 195 keV

Underground measurement at LUNA found no evidence for a low-energy resonance in the

The 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