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Register a new userStrong resonances at high excitation energy in 17O+alpha resonance scattering
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The Thick Target Inverse Kinematic (TTIK) approach was used to measure excitation functions for the elastic 17O ({alpha}, {alpha}) scattering at the initial 17O beam energy of 54.4 MeV. We observed strong peaks corresponding to highly excited {alpha}-cluster states in the 21Ne excitation energy region of 8-16 MeV, which have never been investigated before. Additional tests were done at a 17O beam energy of 56.4 MeV to estimate a possible contribution of resonance inelastic scattering.
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Elastic scattering cross sections of the $^{89}$Y($alpha$,$alpha$)$^{89}$Y reaction have been measured at energies E$_{c.m.}$ = 15.51 and 18.63 MeV. The high precision data for the semi-magic $N = 50$ nucleus $^{89}$Y are used to derive a local potential and to evaluate the predictions of global and regional $alpha$-nucleus potentials. The variation of the elastic alpha scattering cross sections along the $N = 50$ isotonic chain is investigated by a study of the ratios of angular distributions for $^{89}$Y($alpha$,$alpha$)$^{89}$Y and $^{92}$Mo($alpha$,$alpha$)$^{92}$Mo at E$_{c.m.} approx$ 15.51 and 18.63 MeV. This ratio is a very sensitive probe at energies close to the Coulomb barrier, where scattering data alone is usually not enough to characterize the different potentials. Furthermore, $alpha$-cluster states in $^{93}$Nb = $^{89}$Y $otimes$ $alpha$ are investigated.
Determination of the high density behavior of the symmetry energy through the simultaneous measurement of elliptic flow excitation functions of neutrons, protons and light clusters is proposed. The elliptic flow developed in relativistic heavy ion collisions has been proven theoretically and experimentally to have a unique sensitivity and robustness in probing the symmetry energy up to around $2 rho_{o}$. The knowledge of the density dependence of the symmetry energy in a broad range of densities will provide a missing link for astrophysical predictions of the neutron star mass--radius relation. In particular, the data colud provide tighter constraints on the slope parameter L and entirely new limits on $K_{sym}$, the currently poorly constrained symmetry energy curvature parameter.
The $^{17}$O(p,$alpha$)$^{14}$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 $E_{rm R}~=~64.5$~keV resonance strength performed at the Laboratory for Underground Nuclear Astrophysics accelerator has led to the most accurate value to date, $omegagamma = 10.0 pm 1.4_{rm stat} pm 0.7_{rm syst}$~neV, thanks to a significant background reduction underground and generally improved experimental conditions. The (bare) proton partial width of the corresponding state at $E_{rm x} = 5672$~keV in $^{18}$F is $Gamma_{rm p} = 35 pm 5_{rm stat} pm 3_{rm syst}$~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,$alpha$)$^{14}$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.
Results of nuclear resonance fluorescence experiments on $^{117}$Sn are reported. More than 50 $gamma$ transitions with $E_{gamma} < 4$ MeV were detected indicating a strong fragmentation of the electromagnetic excitation strength. For the first time microscopic calculations making use of a complete configuration space for low-lying states are performed in heavy odd-mass spherical nuclei. The theoretical predictions are in good agreement with the data. It is concluded that although the E1 transitions are the strongest ones also M1 and E2 decays contribute substantially to the observed spectra. In contrast to the neighboring even $^{116-124}$Sn, in $^{117}$Sn the $1^-$ component of the two-phonon $[2^+_1 otimes 3^-_1]$ quintuplet built on top of the 1/2$^+$ ground state is proved to be strongly fragmented.
The $^3$H+$^3$He cluster structure in $^6$Li was investigated by the $^3$H($alpha$,$^3$H $^3$He)n kinematically complete experiment at the incident energy $E_alpha$ = 67.2 MeV. We have observed two resonances at $E_x^*$ = 21.30 and 21.90 MeV which are consistent with the $^3$He($^3$H, $gamma$)$^6$Li analysis in the Ajzenberg-Selove compilation. Our data are compared with the previous experimental data and the RGM and CSRGM calculations.
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