T. Szücs

Improved Direct Measurement of the 64.5 keV Resonance Strength in the O 17 (p,α) N 14 Reaction at LUNA

The ^{17}O(p,α)^{14}N reaction plays a key role in various astrophysical scenarios, from asymptotic giant branch stars to classical novae. It affects the synthesis of rare isotopes such as ^{17}O and ^{18}F, which can provide constraints on astrophysical models. A new direct determination of the E_{R}=64.5  keV resonance strength performed at the Laboratory for Underground Nuclear Astrophysics (LUNA) accelerator has led to the most accurate value to date ωγ=10.0±1.4_{stat}±0.7_{syst}  neV, thanks to a significant background reduction underground and generally improved experimental conditions. The (bare) proton partial width of the corresponding state at E_{x}=5672  keV in ^{18}F is Γ_{p}=35±5_{stat}±3_{syst}  neV. This width is about a factor of 2 higher than previously estimated, thus leading to a factor of 2 increase in the ^{17}O(p, α)^{14}N reaction rate at astrophysical temperatures relevant to shell hydrogen burning in red giant and asymptotic giant branch stars. The new rate implies lower ^{17}O/^{16}O ratios, with important implications on the interpretation of astrophysical observables from these stars.

Alpha-induced reaction cross section measurements on

In order to extend the experimental database relevant for the astrophysical -process towards the unexplored heavier mass region, the cross sections of the 151 Eu(�,) 155 Tb and 151 Eu(�,n) 154 Tb reactions have been measured at low energies between 12 and 17MeV using the activation technique. The results are compared with the predictions of statistical model calculations and it is found that the calculations overestimate the cross sections by about a factor of two. A sensitivity analysis shows that this discrepancy is caused by the inadequate description of the �+nucleus channel. A factor of two reduction of the reaction rate of 151 Eu(�,) 155 Tb in -process network calculations with respect to theoretical rates using the optical potential by McFadden and Satchler (1966) is recommended.

^{151}

For the better understanding of the astrophysical gamma-process the experimental determination of low energy proton- and alpha-capture cross sections on heavy isotopes is required. The existing data for the 92Mo(p,gamma)93Tc reaction are contradictory and strong fluctuation of the cross section is observed which cannot be explained by the statistical model. In this paper a new determination of the 92Mo(p,gamma)93Tc and 98Mo(p,gamma)99mTc cross sections based on thick target yield measurements are presented and the results are compared with existing data and model calculations. Reaction rates of 92Mo(p,gamma)93Tc at temperatures relevant for the gamma-process are derived directly from the measured thick target yields. The obtained rates are a factor of 2 lower than the ones used in astrophysical network calculations. It is argued that in the case of fluctuating cross sections the thick target yield measurement can be more suited for a reliable reaction rate determination.

Eu for the astrophysical

When deriving resonance strengths using the thick-target yield approximation, for very narrow resonances it may be necessary to take beam energy straggling into account. This applies to gas targets of a few keV width, especially if there is some additional structure in target stoichiometry or detection efficiency. The correction for this effect is shown and tested on recent studies of narrow resonances in the and reactions.

\gamma

The stable nucleus

-process

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Cross section and reaction rate of 92Mo(p,gamma)93Tc determined from thick target yield measurements

N is the mirror of

Effect of beam energy straggling on resonant yield in thin gas targets: The cases 22Ne(p, γ)23Na and 14N(p, γ)15O

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Determination ofγ-ray widths inN15using nuclear resonance fluorescence

O, the bottleneck in the hydrogen burning CNO cycle. Most of the

Nuclear physics uncertainties of the astrophysical γ-process studied through the 64Zn(p,α)61Cu and 64Zn(p,γ)65Ga reactions

^{15}