Showing papers by "Achim Richter published in 1995"
TL;DR: In this article, recent developments in the field of magnetic dipole excitations in heavy deformed nuclei are discussed by using electromagnetic and hadronic probes of different selectivity, with particular emphasis on the physics of the scissors mode and the spin magnetic dipoles giant resonance and the role neutrons and protons play in their description.
136 citations
TL;DR: In this article, the complete set of resonance parameters for 950 resonances of a superconducting microwave cavity connected to three antennas has been measured and the partial widths are found to follow a Porter-Thomas distribution.
Abstract: The complete set of resonance parameters for 950 resonances of a superconducting microwave cavity connected to three antennas has been measured. This cavity simulates the quantum mechanics of a particle in a Bunimovich stadium. The partial widths are found to follow a Porter-Thomas distribution. The Fourier transforms of the $S$-matrix autocorrelation functions decay algebraically (nonexponentially) in time. These results agree perfectly with the predictions of random-matrix theory. They constitute one of the most stringent tests ever of this expected connection between chaotic dynamics and randommatrix theory.
111 citations
GSI Helmholtz Centre for Heavy Ion Research1, Technische Universität Darmstadt2, Chalmers University of Technology3, University of Mainz4, Spanish National Research Council5, Kurchatov Institute6, Goethe University Frankfurt7, Ruhr University Bochum8, CERN9, Jagiellonian University10, Aarhus University11
TL;DR: In this article, the halo systems Be-11 and Li-11 with a carbon target demonstrate that (n + Li-9) has an (unbound) l = 0 ground state very close to the threshold.
Abstract: Reactions of the halo systems Be-11 and Li-11 (at 460 and 280 MeV/nucleon) with a carbon target demonstrate that (n + Li-9) has an (unbound) l = 0 ground state very close to the threshold. The neutron halo of Li-11 has appreciable (1s(1/2))(2) and (0p(1/2))(2) components.
91 citations
TL;DR: In this paper, a parametric x-ray radiation of type B has been produced with an electron beam of energies between 3.5 and 9.1 MeV from the superconducting accelerator S-DALINAC and diamond of thickness $55.
Abstract: Parametric x-ray radiation of type B has been produced with an electron beam of energies between 3.5 and 9.1 MeV from the superconducting accelerator S-DALINAC and diamond of thickness $55\ensuremath{\mu}\mathrm{m}$. The photon intensity and its energy dependence were determined as a function of the tilt angle of the crystal. The intensity maximum varies with ${\ensuremath{\gamma}}^{2}$ and is about 3 orders of magnitude smaller than channeling radiation. Comparison with theoretical predictions exhibits very good agreement after taking into account effects caused by multiple scattering of the electrons in the crystal.
39 citations
TL;DR: An interacting boson model sum rule for the strength of exciting the magnetic dipole scissors mode is used to relate this strength to the quadrupole deformation, resulting in a parameter-free description of the M1 transition strength over the entire range of nuclei from Nd to W studied experimentally.
Abstract: An interacting boson model sum rule for the strength of exciting the magnetic dipole scissors mode is used to relate this strength to the quadrupole deformation, resulting in a parameter-free description of the {ital M}1 transition strength over the entire range of nuclei from Nd to W studied experimentally. Also, the experimentally established quadratic dependence on the quadrupole ground state deformation is quantitatively reproduced for nuclei up to Yb, but systematic deviations are predicted for heavier nuclei. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.
37 citations
Darmstadt University of Applied Sciences1, Chalmers University of Technology2, University of Mainz3, Spanish National Research Council4, Kurchatov Institute5, Goethe University Frankfurt6, Ruhr University Bochum7, Centre national de la recherche scientifique8, Aarhus University9, Michigan State University10, CERN11
TL;DR: In this paper, the transverse and longitudinal momentum distributions of Li-9 fragments from Li-11 break-up reactions in C, Al and Pb targets have been measured at 280 MeV/u.
37 citations
TL;DR: The MAMI facility with its new generation of 100-duty-cycled electron accelerator has allowed to cover in this experiment the previously not accessible momentum range of 265 as discussed by the authors, where the proton momentum distribution of 16O is linked through the reaction to low-lying discrete states in 15N.
27 citations
TL;DR: In this article, a quasiparticle-phonon model calculation with a configuration space of up to threephonons coupling permits a good description for many of the low-energy states.
26 citations
01 Dec 1995-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, a new system for 180° electron scattering has been put into operation at the superconducting Darmstadt linear electron accelerator S-DALINAC, using a large-aperture QCLAM spectrometer.
Abstract: A new system for 180° electron scattering has been put into operation at the superconducting Darmstadt linear electron accelerator S-DALINAC, using a large-aperture QCLAM spectrometer. The properties of the spectrometer allow for high-resolution 180° measurements with a larger momentum acceptance than that of any previous 180° system, together with unprecedented capabilities for solid angle definition as well as for alignment and monitoring of the system. The large angular acceptance and the precise angular definition allow the solid angle acceptance of the system to be specified by software cuts after the data have been taken, permitting the appropriate balance between maximum statistical precision and maximum longitudinal-to-transverse suppression ratio.
24 citations
TL;DR: In this article, the angular distribution of the loosely bound halo neutron(s) in the projectiles of Li-11 and Be-11 has been derived and a narrow component in transverse momentum that is within uncertainties independent of beam energy and target charge.
Abstract: Neutron angular distributions from violent break-up reactions of Li-11 and Be-11 have been measured at 28 MeV/u and 280 MeV/u and at 41 MeV/u and 460 MeV/u, respectively. The derived neutron momentum distributions show a narrow component in transverse momentum that is within uncertainties independent of beam energy and target charge. This component is suggested to be simply related to the momentum distribution of the loosely bound halo neutron(s) in the projectiles.
23 citations
TL;DR: In this article, the properties of the special levels in 124Te that are strongly populated by thermal neutron-capture γ-rays have been determined with 123Te(n,γ) and 124Te(γ,γ′) experiments.
TL;DR: In this article, a multipole decomposition of the angular correlation functions of the reaction 40Ca(e,e′, α)36Arg is presented in the excitation energy range Ex = 10 − 20 MeV.
TL;DR: In this article, the transverse form factor of the bound proton has been measured in parallel and anti-parallel kinematics over apcffffm range of −120
Abstract: The12C(e, e'p)11B
g.s
reaction has been measured in parallel and anti-parallel kinematics over ap
m range of −120
TL;DR: In this paper, the same authors compared two quasiparticle-phonon model calculations, one with a model space of "quasiparticles" and one extended by "two-phonsons" configurations.
Abstract: The115In(γ, γ′) reaction was measured at the S-DALINAC using bremsstrahlung with endpoint energiesE
0=31, 46 and 52 MeV In the excitation energy range of 1–5 MeV in total 32 transitions were observed, 18 of which were hithertoo unknown The results are compared to two quasiparticle-phonon model calculations, one with a model space of ‘quasiparticle⊗phonon’ and one extended by ‘quasiparticle⊗two-phonon’ configurations A substantial improvement is achieved in the description of low-lying115In states by the consideration of the more complex configurations The calculations quantitatively account for the summed115In(γ, γ′) integrated cross sections and show a comparable amount of fragmentation of the individual transition strengths The model interpretation of the microscopic structure of the experimentally observed transitions is discussed
TL;DR: In this article, the isospin breaking Coulomb matrix element is determined in a two-state model to 〈 H C 〉 = 145(80) keV.
TL;DR: In this article, the linear polarization of channeling radiation produced at the superconducting accelerator S-DALINAC with 62 MeV electrons in silicon and diamond has been measured in the energy range between 50 and 400 keV.
Abstract: Utilizing 90{degree} Compton scattering the linear polarization of channeling radiation produced at the superconducting accelerator S-DALINAC with 62 MeV electrons in silicon and diamond has been measured in the energy range between 50 and 400 keV. Planar channeling radiation due to transitions involving transversal bound as well as unbound states is completely linearly polarized perpendicular to the channeling plane. Axial channeling radiation does not show linear polarization.
TL;DR: A first estimate of the summed magnetic octupole strength to be expected in rare-earth nuclei is obtained using linear energy-weighted sum rules within the proton-neutron interacting boson model.
Abstract: We use linear energy-weighted sum rules within the proton-neutron interacting boson model to deduce a relationship between magnetic dipole and magnetic octupole transition probabilities. We then obtain a first estimate of the summed magnetic octupole strength to be expected in rare-earth nuclei.
Chalmers University of Technology1, Darmstadt University of Applied Sciences2, University of Mainz3, Spanish National Research Council4, Kurchatov Institute5, Goethe University Frankfurt6, Ruhr University Bochum7, Centre national de la recherche scientifique8, Aarhus University9, Jagiellonian University10, Michigan State University11, CERN12
01 Jan 1995-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, recent developments in the field of elementary electric and magnetic nuclear excitations are discussed by using electromagnetic probes of different selectivity, with particular emphasis on the physics of the so-called scissors mode and the spin magnetic dipole giant resonance in heavy deformed nuclei.
Abstract: In three lectures recent developments in the field of elementary electric and magnetic nuclear excitations are discussed by using electromagnetic probes of different selectivity. The first lecture, after a brief reminder of the features of electron and photon scattering at low energy, deals with two selected examples of electric transitions studied in inclusive and exclusive electron and proton scattering in 12C and 40Ca respectively, i.e. the features of an isospin forbidden electric dipole transition in (e,e′) and the structure of electric giant resonances in (e,e′ x) and (p,p′x) reactions are studied. In the second lecture the nature of the orbital and spin magnetic dipole strength with particular emphasis on the physics of the so-called scissors mode and the spin magnetic dipole giant resonance in heavy deformed nuclei are discussed. The third lecture is concerned with three examples, illuminating how subnuclear effects might be detected in the nuclear electromagnetic response at low energy. For this, the prime case for quenching of magnetic dipole spin-flip strength in 48Ca and the evidence for meson exchange current enhancement of isovector magnetic dipole strength in 24Mg are revisited, and finally as an interesting outlook of the field the role of Δ-isobars in the nuclear wave function is illustrated by looking at the idea and at first results from a recent electroproduction experiment of positively and negatively charged pions on 3He at medium energies.