Showing papers by "Achim Richter published in 1991"
TL;DR: In this article, the magnetic dipole spin and orbital response in nuclei are discussed and the dependence of the orbital M1 strength on deformation is investigated in a chain of even-even Sm isotopes spanning a large range of deformation.
52 citations
TL;DR: In heavy deformed even-even nuclei the orbital {ital M}1 strength below 4 MeV excitation, the so-called scissors mode, shows a striking correlation with the {ital E}2 strength to the first excited 2{sup +} states, and a saturation effect is observed before midshell.
Abstract: In heavy deformed even-even nuclei the orbital {ital M}1 strength below 4 MeV excitation, the so-called scissors mode,'' shows a striking correlation with the {ital E}2 strength to the first excited 2{sup +} states. A saturation effect, common to both {ital E}2 and {ital M}1 transitions, is observed before midshell. The correlation and the saturation effect are discussed.
40 citations
TL;DR: In this article, the authors investigated the continuous particle spectra following the beta decay of the neutron-rich nuclei that terminate the mass 6, 8, 9 and 11 isobaric chains.
Abstract: We have investigated the continuous particle spectra following the beta decay of the neutron-rich nuclei that terminate the mass 6, 8, 9 and 11 isobaric chains. Strong beta transitions feeding the very top of the spectrum are found systematically. The favoured states are within a few MeV of the energy of the initial state. This phenomenon seems to be linked to the occurrence of a di-neutron structure or neutron halo in the drip-line nuclei.
31 citations
TL;DR: In this article, large integrated cross sections for photoexcitation of 115Inm have been detected around Ex=3MeV and it is shown that the g.s. transition strength is largely confined to the same energy region and the intermediate excited states are identified.
22 citations
TL;DR: Integrated cross sections for resonant photoactivation of isomeric levels in {sup 87}Sr, {sup 111}Cd, and {sup 113,115}In have been calculated from recent nuclear structure data and compared to those experimental results which assert that nonresonant contributions are important.
Abstract: The most recent investigation of the photoactivation of isomeric nuclei reported by Kr{hacek c}mar {ital et} {ital al}. continues to contain a strong contribution from nonresonant channels. In this Comment we report that integrated cross sections for resonant photoactivation of isomeric levels in {sup 87}Sr, {sup 111}Cd, and {sup 113,115}In have been calculated from recent nuclear structure data and compared to those experimental results which assert that nonresonant contributions are important. The latter have shown systematically smaller values and the amount of missing resonant strength can be correlated to the magnitude of nonresonant cross section found in these investigations. Monte Carlo simulations of realistic experimental geometries display important components in the photon fields, resulting from environmental Compton scattering, which have been omitted in previous analyses of experimental data. The strength and shape of this contribution as a function of the experimentally important parameters suggest that the data can be explained entirely on the basis of a resonant excitation mechanism without any need to introduce a nonresonant contribution.
10 citations
TL;DR: In this paper, a set of wave functions was derived to describe the 14N ground state and the isospin triplet consisting of the 14C ground state, the first excited state of 14N at 2.313 MeV and the 14O ground state.
Abstract: A set of phenomenological wave functions has been derived to describe the14N ground state and the isospin triplet consisting of the14C ground state, the first excited state of14N at 2.313 MeV and the14O ground state. Elastic and inelastic electron scattering form factors, the magnetic moment of the14N ground state and the shape factors in theβ
± decay have been employed in a multiparameter fitting procedure to determine the amplitudes of the wave functions inL-S coupling. The inclusion of the beta decay observables in the fit has become possible for the first time since exact formulas for the shape factor in higher order do exist. The set of wave functions deduced exhibit predominately anL=0 contribution for the 0+; 1 states andL=1 and 2 contributions of nearly equal weight for the 1+; 0 state. It was observed that the inclusion of the shape factors allowed a more stringent determination of the amplitudes compared to previous attempts reported in the literature and led in the case of the 0+; 1 states to wave functions that show a small but noticeable difference within the isospin triplet. Besides the observables used for the fit, the radiative widthΓ
γ
(M1) of the 2.313 MeV state in14N can be described quite well with the derived wave functions, and in addition it has become possible to predict the pathological largeft
− value of the14C decay and theft
+ value of the14O decay precisely. The wave functions are also applied to calculate the14N(γ,π
+) cross section.
9 citations
TL;DR: The excitation function for the long-lived isomer indicated that the isomer was populated by resonant absorption through isolated intermediate states having integrated cross sections in excess of 10{sup {minus}26} cm{sup 2} keV, i.e., values about 100 times larger than most ({gamma},{gamma}{prime}) activation reactions reported previously.
Abstract: Photoexcitation of the long-lived isomers {sup 123}Te{sup {ital m}}, {ital T}{sub 1/2}=119.7 d, and {sup 125}Te{sup {ital m}}, {ital T}{sub 1/2}=58 d, was produced with bremsstrahlung from the superconducting Darmstadt linear accelerator. The excitation function for the reaction {sup 123}Te({gamma},{gamma}{prime}){sup 123}Te{sup {ital m}} was measured between 2 and 6 MeV. It indicated that the isomer was populated by resonant absorption through isolated intermediate states having integrated cross sections in excess of 10{sup {minus}26} cm{sup 2} keV, i.e., values about 100 times larger than most ({gamma},{gamma}{prime}) activation reactions reported previously. An excitation function was also obtained for the reaction {sup 125}Te({gamma},{gamma}{prime}){sup 125}Te{sup {ital m}} in this energy range.
9 citations
01 Jul 1991-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: The S-DALINAC Free Electron Laser (FEL) as discussed by the authors is a free electron laser in the near-infrared region that is intended to make use of an electron beam variable in energy between 35 and 50 MeV, a hybrid undulator (K ≥ 1.2; λu = 3.2 cm), and a nearly concentric optical cavity consisting of two spherical dielectric mirrors of 75 mm diameter separated by 15 m and mounted inside vacuum chambers.
Abstract: At the new superconducting 130 MeV electron accelerator, S-DALINAC, a free electron laser in the near-infrared region is presently under construction. It is intended to make use of an electron beam variable in energy between 35 and 50 MeV, a hybrid undulator (K ≥ 1.2; λu = 3.2 cm) constructed in the wedged pole configuration with 80 periods achieving a peak magnetic field on axis in excess of 0.4 T, and a nearly concentric optical cavity consisting of two spherical dielectric mirrors of 75 mm diameter separated by 15 m and mounted inside vacuum chambers. With this setup it will become possible to cover a wavelength region in the near infrared from 2.8–5.7 μm. The FEL will be operating continuously generating laser pulses of 1.9 ps duration at a repetition rate of 10 MHz. According to simulations the output peak power amounts to several hundred kilowatts. The properties of the FEL radiation will be unique regarding the region of wavelength, tunability, pulse time structure and cw mode. First experiments are expected to be carried out in 1991.
5 citations
01 Jul 1991-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, an FEL operating in the near infrared (λ = 2.5 5μm) is under construction at the superconducting accelerator which has originally been designed for nuclear physics experiments requiring electron beams of low peak currents.
Abstract: Presently an FEL operating in the near infrared (λ = 2.5 5μm) is under construction at the superconducting accelerator which has originally been designed for nuclear physics experiments requiring electron beams of low peak currents. The redesign of the present injection with the purpose of achieving higher peak currents for the operation of the FEL and the resulting requirements for the individual injection components will be described. Furthermore the experimental results obtained with an injection test stand consisting of the electron gun, the chopper-resonator and some electron beam diagnostics are discussed.
3 citations
15 Oct 1991
TL;DR: In this paper, the authors identified the so-called M1 scissors mode near 3 MeV excitation energy and found some E1 transitions with strengths up to several mWu.
Abstract: High resolution Nuclear Resonance Fluorescence (NRF) experiments have been carried out to study low lying dipole excitations in rare earth nuclei. In particular, we identified the so called M1 scissors mode near 3 MeV excitation energy. At the same time we found some E1 transitions with strengths up to several mWu. The inspection of the measured decay branching ratios suggests K‐mixing for a few states while giving overall evidence for a good K‐quantum number at 3 MeV.
1 citations