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Register a new userMeasurement of (alpha,n) reaction cross sections of erbium isotopes for testing astrophysical rate predictions
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The $gamma$-process in core-collapse and/or type Ia supernova explosions is thought to explain the origin of the majority of the so-called $p$ nuclei (the 35 proton-rich isotopes between Se and Hg). Reaction rates for $gamma$-process reaction network studies have to be predicted using Hauser-Feshbach statistical model calculations. Recent investigations have shown problems in the prediction of $alpha$-widths at astrophysical energies which are an essential input for the statistical model. It has an impact on the reliability of abundance predictions in the upper mass range of the $p$ nuclei. With the measurement of the $^{164,166}$Er($alpha$,n)$^{167,169}$Yb reaction cross sections at energies close to the astrophysically relevant energy range we tested the recently suggested low energy modification of the $alpha$+nucleus optical potential in a mass region where $gamma$-process calculations exhibit an underproduction of the $p$ nuclei. Using the same optical potential for the $alpha$-width which was derived from combined $^{162}$Er($alpha$,n) and $^{162}$Er($alpha$,$gamma$) measurement makes it plausible that a low-energy modification of the optical $alpha$+nucleus potential is needed.
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The 106Cd(alpha,gamma)110Sn reaction cross section has been measured in the energy range of the Gamow window for the astrophysical p-process scenario. The cross sections for 106Cd(alpha,n)109Sn and for 106Cd(alpha,p)109In below the (alpha,n) threshold have also been determined. The results are compared with predictions of the statistical model code NON-SMOKER using different input parameters. The comparison shows that a discrepancy for 106Cd(alpha,gamma)110Sn when using the standard optical potentials can be removed with a different alpha+106Cd potential. Some astrophysical implications are discussed.
The cross sections of the nuclear reactions induced by neutrons at $E_n$= 14.6 MeV on the isotopes of Dy, Er, Yb with emission of neutrons, proton and alpha-particle are studied by the use of new experimental data and different theoretical approaches. New and improved experimental data are measured by the neutron-activation technique. The experimental and evaluated data from EXFOR, TENDL, ENDF libraries are compared with different systematics and calculations by codes of EMPIRE~3.0 and TALYS~1.2. Contribution of pre-equilibrium decay is discussed. Different systematics for estimations of the cross-sections of considered nuclear reactions are tested.
We systematically analyze total reaction cross sections of carbon isotopes with N=6--16 on a $^{12}$C target for wide range of incident energy. The intrinsic structure of the carbon isotope is described by a Slater determinant generated from a phenomenological mean-field potential, which reasonably well reproduces the ground state properties for most of the even $N$ isotopes. We need separate studies not only for odd nuclei but also for $^{16}$C and $^{22}$C. The density of the carbon isotope is constructed by eliminating the effect of the center of mass motion. For the calculations of the cross sections, we take two schemes: one is the Glauber approximation, and the other is the eikonal model using a global optical potential. We find that both of the schemes successfully reproduce low and high incident energy data on the cross sections of $^{12}$C, $^{13}$C and $^{16}$C on $^{12}$C. The calculated reaction cross sections of $^{15}$C are found to be considerably smaller than the empirical values observed at low energy. We find a consistent parameterization of the nucleon-nucleon scattering amplitude, differently from previous ones. Finally, we predict the total reaction cross section of $^{22}$C on $^{12}$C.
The total cross sections for the 120Te(p,gamma)121I and 120Te(p,n)120I reactions have been measured by the activation method in the effective center-of-mass energies between 2.47 MeV and 7.93 MeV. The targets were prepared by evaporation of 99.4 % isotopically enriched 120Te on Aluminum and Carbon backing foils, and bombarded with proton beams provided by the FN tandem accelerator at the University of Notre Dame. The cross sections and $S$ factors were deduced from the observed gamma ray activity, which was detected off-line by two Clover HPGe detectors mounted in close geometry. The results are presented and compared with the predictions of statistical model calculations using the codes NON-SMOKER and TALYS.
The stellar reaction rates of radiative $alpha$-capture reactions on heavy isotopes are of crucial importance for the $gamma$ process network calculations. These rates are usually derived from statistical model calculations, which need to be validated, but the experimental database is very scarce. This paper presents the results of $alpha$-induced reaction cross section measurements on iridium isotopes carried out at first close to the astrophysically relevant energy region. Thick target yields of $^{191}$Ir($alpha$,$gamma$)$^{195}$Au, $^{191}$Ir($alpha$,n)$^{194}$Au, $^{193}$Ir($alpha$,n)$^{196m}$Au, $^{193}$Ir($alpha$,n)$^{196}$Au reactions have been measured with the activation technique between E$_alpha = 13.4$ MeV and 17 MeV. For the first time the thick target yield was determined with X-ray counting. This led to a previously unprecedented sensitivity. From the measured thick target yields, reaction cross sections are derived and compared with statistical model calculations. The recently suggested energy-dependent modification of the $alpha$+nucleus optical potential gives a good description of the experimental data.
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