K. Bangert

Bound state M1 transitions in sd-shell nuclei☆

Abstract Nuclear resonance fluorescence experiments with unpolarized and linearly polarized bremsstrahlung and high-resolution Ge(Li) detectors have yielded model-independent values of magnetic dipole excitation strengths to highly excited states in 20,22 Ne, 24,26 Mg, 28,30 Si, and 32,34 S. The measured B ( M 1) values are quenched relative to the j - j limit of the shell model, but are in general agreement with predictions of recent shell-model calculations which treat intra-sd-shell configuration mixing completely.

Ground state dipole transitions in 58Ni

Abstract Nuclear resonance fluorescence measurements on 58 Ni with bremsstrahlung and Ge(Li) detectors were performed to search for bound state dipole excitations. Ten levels with ground state decay widths larger than 0.3 eV have been observed in the energy region between 6 and 10 MeV for which precise excitation energies, spins and lifetimes are reported. The measured transition probabilities are compared with theoretical estimates of E1 and M1 strength in 58 Ni. Since the 58 Ni (γ, γ) cross sections were determined relative to strong transitions in 208 Pb, the results of a separate 208 Pb(γ, γ) measurement are also presented.

A comparative study of the electric giant dipole resonance of 24−26Mg☆

Abstract The electric giant dipole resonance of 24−26 Mg has been explored up to 30 MeV excitation energy with bremsstrahlung. ΔE , E spectra of charged photo-particles and spectra of prompt deexcitation γ-rays from excited residual nuclear states were obtained at various bremsstrahlung endpoint energies. The 25 Mg(γ, p 0 ), (γ, d), 24,25 Mg(γ, α) differential cross sections as well as 24−26 Mg ( γ , xγ ′) integrated cross sections are presented. The results are discussed in terms of one-particle, one-hole excitations and isospin composition of giant resonance states. A comparison with calculations for 24 Mg gives poor agreement. Excitations from deeper shells were found in the giant dipole resonance of 24 Mg, but do not seem to be concentrated at higher energies. In 25 Mg, only weak excitations of this kind were found, and they are completely absent in 26 Mg.

Parities of dipole ground-state transitions in 52Cr☆

Abstract Nuclear resonance fluorescence experiments with polarized bremsstrahlung were performed to search for magnetic dipole strength. Previous interpretations that states at 7730, 7896 and 9787 keV in 52 Cr are due to M1 excitations can not be confirmed. These transitions are unexpectedly strong E1 excitations, exceeding 1 m Weisskopf unit in strength. The remaining identified M1 strength of ΣB (M1)↑ = 2.5 ± 0.7 μ k 2 is in agreement with the observation of missing M1 strength in heavy nuclei.

The photodisintegration of6Li and7Li

The photodisintegration of the stable Lithium isotopes has been investigated by spectroscopy of the emitted charged particles using the Giessen bremsstrahlung facility. Protons, deuterons, tritons,3He and alpha particles were detected and identified up to 20MeV particle energy. Angular distributions were measured using γ-ray energies up toEγ =50 MeV. They are compared with theoretical predictions and with other experiments. A remarkable low (γ, t)-cross section was found for both isotopes in disagreement to previous measurements using virtual photons. Coincidence measurements between the emitted particles were performed in order to study the manybody-breakups of7Li.

Lifetimes of highly excited states in 34S from nuclear resonance fluorescence

Abstract The 34 S(γ, γ) reaction was employed to study highly excited states in 34 S. Precise excitation energies and photon scattering cross sections of twelve levels between 7 and 11 MeV were obtained using bremsstrahlung and high resolution Ge(Li) detectors. Six new states were found and lifetimes for all states were derived under the assumption that ground state transitions were observed. The lowest T = 2 state in 34 S was identified by the Coulomb displacement energy relative to the 34 P ground state and by comparison of its Γ 0 γ width with the Gamow-Teller strength of the analogue β-decay. The results are compared to shell model calculations for the distribution of the M1 strength in 34 S.

The decay of the18O giant dipole resonance to excited residual nuclear states

The decay of the18O GDR to excited residual nuclear states has been examined by measuring spectra of prompt deexcitationγ-rays. The target was irradiated by bremsstrahlung with endpoint energies of 23.5 and 28 MeV. “Bremsstrahlung-weighted” integrated cross sections are given for the population of the residual nuclear states in17O,17N,16O and14C. Proton decay to excited states in17N is remarkably weak. It seems that 1p3/2 excitations play only a minor role in the18O GDR.

Charged photoparticles from the 18O giant resonance

Abstract Emission of charged photoparticles from the 18 O giant E1 resonance region was investigated at the University of Giessen electron linac at bremsstrahlung endpoint energies of 24 and 32 MeV. Spectra of protons, deuterons, tritons and α-particles were measured at six angles. Proton decay shows strong transitions to excited states in 17 N. Deuterons and tritons have a nearly isotropic angular distribution. The 18 O( γ , t 0 ) 15 N and the 18 O( γ , α 0 ) 14 C cross sections are determined in the giant E1 resonance region. E1 and E2 18 O( γ , α 0 14 C cross sections are derived from the angular distribution measurement.

Parities of strong dipole ground state transitions in88Sr

The unknown parities of five strong dipole states between 6 and 8 MeV in88Sr are shown to be negative.

On-line acquisition of N-fold coincidences at a pulsed accelerator☆

Abstract A general data recording system was developed to measure energy and type of light charged particles emitted by photonuclear reactions. Manifold coincidence spectra of particles from different detectors can be accumulated and represented. An application is given for the 7Li(γ, t)4He reaction.