K. D. Schilling

Bio: K. D. Schilling is an academic researcher from Helmholtz-Zentrum Dresden-Rossendorf. The author has contributed to research in topics: Neutron & Dipole. The author has an hindex of 17, co-authored 49 publications receiving 935 citations.

The photon-scattering facility at the superconducting electron accelerator ELBE

Abstract: A new facility for the production of polarised bremsstrahlung has been built at the superconducting electron accelerator ELBE of the Forschungszentrum Rossendorf. The bremsstrahlung facility and the setup for photon-scattering experiments are designed such that the background radiation caused by the scattering of photons and the production of neutrons is minimised. The sensitive setup in connection with electron energies up to 20 MeV and average currents up to 1 mA delivered by the ELBE accelerator enables novel experiments using photon-induced reactions. First results of photon-scattering experiments are presented.

Pygmy dipole strength in Zr 90

Abstract: The dipole response of the $N=50$ nucleus $^{90}\mathrm{Zr}$ was studied in photon-scattering experiments at the electron linear accelerator ELBE with bremsstrahlung produced at kinetic electron energies of 7.9, 9.0, and 13.2 MeV. We identified 189 levels up to an excitation energy of 12.9 MeV. Statistical methods were applied to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. In this way we derived the photoabsorption cross section up to the neutron-separation energy. This cross section matches well the photoabsorption cross section obtained from ($\ensuremath{\gamma}$, $n$) data and thus provides information about the extension of the dipole-strength distribution toward energies below the neutron-separation energy. An enhancement of $E1$ strength has been found in the range of 6 to 11 MeV. Calculations within the framework of the quasiparticle-phonon model ascribe this strength to a vibration of the excessive neutrons against the $N=Z$ neutron-proton core, giving rise to a pygmy dipole resonance.

Pygmy dipole strength in 90Zr

Abstract: The dipole response of the N=50 nucleus 90Zr was studied in photon-scattering experiments at the electron linear accelerator ELBE with bremsstrahlung produced at kinetic electron energies of 7.9, 9.0, and 13.2 MeV. We identified 189 levels up to an excitation energy of 12.9 MeV. Statistical methods were applied to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. In this way we derived the photoabsorption cross section up to the neutron-separation energy. This cross section matches well the photoabsorption cross section obtained from (gamma,n) data and thus provides information about the extension of the dipole-strength distribution toward energies below the neutron-separation energy. An enhancement of E1 strength has been found in the range of 6 MeV to 11 MeV. Calculations within the framework of the quasiparticle-phonon model ascribe this strength to a vibration of the excessive neutrons against the N = Z neutron-proton core, giving rise to a pygmy dipole resonance.

Pygmy Dipole Strength in $^{86}$Kr and Systematics of $N=50$ Isotones

Abstract: The dipole strength of the $N=50$ nucleus ${}^{86}$Kr was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of energies of 7.9 and 11.2 MeV delivered by the linear accelerator ELBE as well as using quasimonoenergetic and linearly polarized $\ensuremath{\gamma}$ rays of 10 energies within the range from 4.7 to 9.3 MeV delivered by the HI$\ensuremath{\gamma}$S facility. A high-pressure gas target was used. We identified 39 levels up to an excitation energy of 10.1 MeV. Simulations of $\ensuremath{\gamma}$-ray cascades were performed to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. The photoabsorption cross section derived in this way up to the neutron-separation energy is combined with the photoabsorption cross section obtained from a $(\ensuremath{\gamma},n)$ experiment at HI$\ensuremath{\gamma}$S. The enhanced $E1$ strength found in the range from 6 to 10 MeV is compared with the ones in the $N$ $=$ 50 isotones ${}^{88}$Sr, ${}^{90}$Zr, and ${}^{92}$Mo and with predictions of calculations within the quasiparticle-phonon model.

Low-energy tail of the giant dipole resonance in Mo 98 and Mo 100 deduced from photon-scattering experiments

Abstract: Dipole-strength distributions in the nuclides $^{98}\mathrm{Mo}$ and $^{100}\mathrm{Mo}$ up to the neutron-separation energies have been studied in photon-scattering experiments at the bremsstrahlung facility of the Forschungszentrum Dresden-Rossendorf. To determine the dipole-strength distributions up to the neutron-emission thresholds, statistical methods were developed for the analysis of the measured spectra. The measured spectra of scattered photons were corrected for detector response and atomic background by simulations using the code GEANT3. Simulations of $\ensuremath{\gamma}$-ray cascades were performed to correct the intensities of the transitions to the ground state for feeding from higher-lying levels and to determine their branching ratios. The photoabsorption cross sections obtained for $^{98}\mathrm{Mo}$ and $^{100}\mathrm{Mo}$ from the present $(\ensuremath{\gamma},{\ensuremath{\gamma}}^{'})$ experiments are combined with $(\ensuremath{\gamma},n)$ data from literature, resulting in a photoabsorption cross section covering the range from 4 to about 15 MeV of interest for network calculations in nuclear astrophysics. Novel information about the low-energy tail of the giant dipole resonance and its energy dependence is derived. The photoabsorption cross sections deduced from the present photon-scattering experiments are compared with existing data from neutron capture and $^{3}\mathrm{He}$-induced reactions.

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Transition probability from the ground to the first-excited 2^+ state of even-even nuclides

Abstract: Adopted values for the reduced electric quadrupole transition probability, B(E2)↑, from the ground state to the first-excited 2+ state of even–even nuclides are given in Table I. Values of τ, the mean life of the 2+ state; E, the energy; and β, the quadrupole deformation parameter, are also listed there. The ratio of β to the value expected from the single-particle model is presented. The intrinsic quadrupole moment, Q0, is deduced from the B(E2)↑ value. The product E×B(E2)↑ is expressed as a percentage of the energy-weighted total and isoscalar E2 sum-rule strengths. Table II presents the data on which Table I is based, namely the experimental results for B(E2)↑ values with quoted uncertainties. Information is also given on the quantity measured and the method used. The literature has been covered to November 2000. The adopted B(E2)↑ values are compared in Table III with the values given by systematics and by various theoretical models. Predictions of unmeasured B(E2)↑ values are also given in Table III.

The s process: Nuclear physics, stellar models, and observations

Abstract: Nucleosynthesis in the $s$ process takes place in the He-burning layers of low-mass asymptotic giant branch (AGB) stars and during the He- and C-burning phases of massive stars. The $s$ process contributes about half of the element abundances between Cu and Bi in solar system material. Depending on stellar mass and metallicity the resulting $s$-abundance patterns exhibit characteristic features, which provide comprehensive information for our understanding of the stellar life cycle and for the chemical evolution of galaxies. The rapidly growing body of detailed abundance observations, in particular, for AGB and post-AGB stars, for objects in binary systems, and for the very faint metal-poor population represents exciting challenges and constraints for stellar model calculations. Based on updated and improved nuclear physics data for the $s$-process reaction network, current models are aiming at an ab initio solution for the stellar physics related to convection and mixing processes. Progress in the intimately related areas of observations, nuclear and atomic physics, and stellar modeling is reviewed and the corresponding interplay is illustrated by the general abundance patterns of the elements beyond iron and by the effect of sensitive branching points along the $s$-process path. The strong variations of the $s$-process efficiency with metallicity bear also interesting consequences for galactic chemical evolution.

Shape coexistence in atomic nuclei

Abstract: Shape coexistence in nuclei appears to be unique in the realm of finite many-body quantum systems It differs from the various geometrical arrangements that sometimes occur in a molecule in that in a molecule the various arrangements are of the widely separated atomic nuclei In nuclei the various ''arrangements'' of nucleons involve (sets of) energy eigenstates with different electric quadrupole properties such as moments and transition rates, and different distributions of proton pairs and neutron pairs with respect to their Fermi energies Sometimes two such structures will ''invert'' as a function of the nucleon number, resulting in a sudden and dramatic change in ground-state properties in neighboring isotopes and isotones In the first part of this review the theoretical status of coexistence in nuclei is summarized Two approaches, namely, microscopic shell-model descriptions and mean-field descriptions, are emphasized The second part of this review presents systematic data, for both even- and odd-mass nuclei, selected to illustrate the various ways in which coexistence is observed in nuclei The last part of this review looks to future developments and the issue of the universality of coexistence in nuclei Surprises continue to be discovered With the major advances in reaching to extremes of proton-neutronmore » number, and the anticipated new ''rare isotope beam'' facilities, guidelines for search and discovery are discussed« less