M. Chernykh

Pair decay width of the Hoyle state and carbon production in stars

The pair decay width of the first excited 0+ state in 12C (the Hoyle state) is deduced from a novel analysis of the world data on inelastic electron scattering covering a wide momentum transfer range, thereby resolving previous discrepancies. The extracted value ?? = (62.3 ? 2.0) ?eV is independently confirmed by new data at low momentum transfers measured at the S-DALINAC and reduces the uncertainty of the literature values by more than a factor of three. A precise knowledge of ?? is mandatory for quantitative studies of some key issues in the modeling of supernovae and of asymptotic giant branch stars, the most likely site of the slow-neutron nucleosynthesis process.

Electron scattering on the Hoyle state and carbon production in stars

High‐resolution inelastic electron scattering experiments were performed at the S‐DALINAC for a precise determination of the partial pair width Γπ of the second Jπ = 0+ state, the so‐called Hoyle state, in 12C. Results for the monopole matrix element (directly related to Γπ) from a nearly model‐independent analysis based on an extrapolation of low‐q data to zero momentum transfer are presented. Additionally, a Fourier‐Bessel analysis of the transition form factor is discussed. The combined result of both methods leads to a pair width Γπ62.2(10) μeV.

E2 strengths and transition radii difference of one-phonon 2 + states of 92 Zr from electron scattering at low momentum transfer

Background: Mixed-symmetry 2 + states in vibrational nuclei are characterized by a sign change between dominant proton and neutron valence-shell components with respect to the fully symmetric 2 + state. The sign can be measured by a decomposition of proton and neutron transition radii with a combination of inelastic electron and hadron scattering [C. Walz et al., Phys. Rev. Lett. 106, 062501 (2011)]. For the case of 92 Zr, a difference could be experimentally established for the neutron components, while about equal proton transition radii were indicated by the data. Purpose: Determination of the ground-state (g.s.) transition strength of the mixed-symmetry 2 + state and verification of the expected vanishing of the proton transition radii difference between the one-phonon 2 + states in 92 Zr. Method:Differential cross sections for the excitation of one-phonon 2 + and 3 − states in 92 Zr have been measured with the (e, e � ) reaction at the S-DALINAC in a momentum transfer range q � 0.3‐0. 6f m −1 . Results: Transition strengths B(E2;2 + → 0 + ) = 6.18(23), B(E2;2 + → 0 + ) = 3.31(10), and B(E3;3 − → 0 + ) = 18.4(1.1) Weisskopf units are determined from a comparison of the experimental cross sections to quasiparticle-phonon model (QPM) calculations. It is shown that a model-independent plane wave Born approximation (PWBA) analysis can fix the ratio of B(E2) transition strengths to the 2 +,2 states with a precision of about 1%. The method furthermore allows to extract their proton transition radii difference. With the present /

One-phonon excitations in 92Zr from electron scattering

Low-lying collective vibrational excitations of 92Zr have been investigated with electron scattering at the S-DALINAC. The form factors of isospin polarized one-quadrupole phonon states of 92Zr at the Z = 40 proton subshell closure have been measured and the momentum-transfer dependence of the form factors for the one-quadrupole phonon states have been compared to the prediction of the Quasiparticle Phonon Model. The E2 transition strengths of the one-quadrupole phonon states and the E3 transition strength of the one-octupole phonon state have been extracted. A comparison to the data on 94Mo and previous spectroscopic information on mixed-symmetric states (MSSs) of 92Zr will be given.

Nature of Symmetric and Mixed-Symmetric 2+ States in 92Zr from Electron Scattering

To measure the form factor of isospin polarized one‐quadrupole phonon states of 92Zr at the Z = 40 proton subshell closure and to compare it to the momentum‐transfer dependence of the form factors for the one‐quadrupole phonon states predicted by the Quasiparticle Phonon Model, the 2+ states of 92Zr have been investigated with an electron scattering experiment at the S—DALINAC. The relative E2 excitation strength to off‐yrast 22+ state was also extracted in a model‐independent systematic procedure. A comparison with the data on 94Mo and previous spectroscopic information on MSSs of 92Zr will be given.To measure the form factor of isospin polarized one‐quadrupole phonon states of 92Zr at the Z = 40 proton subshell closure and to compare it to the momentum‐transfer dependence of the form factors for the one‐quadrupole phonon states predicted by the Quasiparticle Phonon Model, the 2+ states of 92Zr have been investigated with an electron scattering experiment at the S—DALINAC. The relative E2 excitation strength to off‐yrast 22+ state was also extracted in a model‐independent systematic procedure. A comparison with the data on 94Mo and previous spectroscopic information on MSSs of 92Zr will be given.

Photo‐fission at the S‐DALINAC

Experiments on photo-induced fission of 238U and 234U using bremsstrahlung with endpoint energies between 6 MeV and 9 MeV have been carried out at the superconducting Darmstadt electron linear acce ...

The Role of the 96 keV Level in the 19O(β–)19F Process at Stellar Temperatures

From isobaric analog symmetry arguments and nuclear shell model calculations, we evaluate the temperature dependence of the beta-decay rates of the ground state and first excited state at an excitation energy of 96 keV in 19O. It is shown that the decay from the excited level exceeds that of the ground state for T9 > 1. This feature may be of significance in the r-process and explosive nucleosynthesis.