H. Rebel

The odd-even staggering of the nuclear charge radii of Pb isotopes

Abstract Previous laser-spectroscopic studies of the hyperfine structure splittings and isotope shifts of the (6p 2 3 P 0 -6p7s 3 P 1 ; 283.3 nm) PbI resonance line have been extended to further radioactive Pb nuclides: 196, 197, 197m, 211, 214 Pb Using an improved theoretical result for the specific mass shift, we recalibrate the isotope shifts of the full series ( A = 196–214) of measured isotope shifts in terms of the nuclear parameter and determine the odd-even staggering parameters. The variation of the nuclear charge radii of the Pb nuclides exhibits distinct shell effects, and the odd-even staggering shows a conspicuous trend, being more pronounced for neutron-deficient Pb isotopes.

Laserspectroscopic studies of collective properties of neutron deficient Ba Nuclei

Isotope shifts and hyperfine structure of the BaI resonance-line (λ=553.6 nm) have been measured by dye laser induced resonance fluorescence on an atomic beam for135m, 129g, 129m, 126Ba thus extending previous high resolution measurements of neutron deficient Ba nuclides (N<82). The experimental results, now available for 16Ba isotopes and isomers withA=140−126, are used to deduce differences of rms charge radii, magnetic dipole and electric quadrupole moments. While the groundstates display a pronounced odd-even staggering the h 11/2− isomers135mBa and133mBa show a decreased staggering. Conspicuously the isomer shift of theg 7/2+ isomer129mBa proves to be negative. The nuclear structure information is discussed in the context of gammaspectroscopic studies of transitional nuclei with 50<N,Z<82 and on the basis of a quasi-particle-plus-triaxial rotor model. The isotope shift discrepancy observed is fairly well described by the droplet model.

Optical model studies of 6Li elastic scattering at 156 MeV

Abstract Differential cross sections for 6Li elastic scattering at 156 MeV from 12C, 40Ca, 90Zr and 208Pb are presented. The sensitivity to various potential forms is established by using Saxon-Woods, Saxon-Woods-squared and density-independent folded potentials. The extent to which the experimental data determine the potentials and related quantities is discussed.

Inclusive break-up reactions of 6Li at an incident energy of 26 MeV/nucleon

Abstract Inclusive charged particle spectra were measured from nuclear reactions induced by 156 MeV 6 Li on 40 Ca. At forward angles the spectra exhibit broad break-up distributions centered around the energy corresponding to the beam velocity. The double differential cross sections together with previous results for a 208 Pb target were analyzed in the framework of the DWBA approach to projectile break-up taking into account elastic and inelastic reactions of the break-up fragments. The high energy tails of the background due to preequilibrium emission of complex charged particles were estimated on the basis of the coalescence model.

Projectile break-up in continuous particle spectra from nuclear reactions induced by 156 MeV6Li

The break-up of 156 MeV6Li ions colliding with12C,60Ni,90Zr,120Sn and208Pb has been experimentally studied. It was found that the break-up cross section decreases rapidly with increasing emission angles of the fragments and increases with increasing target mass. It comprises a fairly large fraction of the total reaction cross section. The observed features suggest that the6Li fragmentation is mainly a peripheral process, and is dominated by the cluster properties of the incident projectile. A simple plane-wave break-up model gives a rather good description of the shapes of the break-up bumps. The angular distributions of the fragments emitted in the6Li+208Pb reaction reveal the transition from peripheral break-up to incomplete fusion processes by which beam-velocity fragments are captured by the target nucleus. In addition to the (α+d) dissociation the (3He+t) break-up has been observed, but the triton spectra appear to be rather complex indicating further components due to more complicated reaction paths.

Nuclear matter sizes and isoscalar octupole transition rates of204,206,208Pb from 104 MeV α-particle scattering

Differential cross sections for elastic and inelastic scattering of 104 MeVα-particles from204,206,208Pb were measured with high angular accuracy. The experimental results were analysed on the basis of a semimicroscopic folding model in order to determine the matter distributions at the nuclear surface and the transition densities. Using phenomenological parametrizations of the densities the analyses of elastic scattering yield rms radii of 〈r2〉1/2=5.55±0.06 (204Pb), 5.57±0.06 (206Pb), 5.63±0.05 (208Pb) fm. Various sensitivities affecting the results were studied. From the inelastic cross sections for the 31−-states octupole transition probabilities and transition radii were derived by using different methods proposed in literature.

Optical potentials and isoscalar transition rates from 104 MeV alpha-particle scattering by the N=28 isotones48Ca,50Ti and52Cr

Precisely measured differential cross sections for elastic and inelastic scattering from 104 MeV alpha-particles by48Ca,50Ti and52Cr are reported. The analyses aim primarily at the determination of strength, radial shapes and deformation of the scattering potentials, looking for isotonic differences ofN=28 isotones. The mean square radii of the (real) potentials are discussed in terms of mean square radius differences of the matter distributions. The isoscalar transition rates derived by coupled channel analyses of the measured cross sections are compared with electromagnetic rates. In addition to the analyses on the basis of a slightly generalized extended optical model a semi-microscopic deformed folding model has been applied, using a density-dependent effective alpha-bound nucleon interaction. Though an excellent description of the data over the full angular range is obtained the resulting values of the deformation parameters appear to be not consistent with results from various different methods.

Transfer of6Li break-up fragments at6Li projectile energies far above the coulomb barrier

Abstract Transfer of beam-velocity fragments has been experimentally investigated in 6 Li induced reactions on 208 Pb and 209 Bi in the energy range E Li = 60–156MeV The experimental techniques involve the observation of the target residues and measurements of the recoil ranges of heavy residual nuclei produced by charged particle bombardment. The determination of the recoil energy enables the discrimination of different reaction paths leading to the same residual nuclei.( 6 Li, xn+p) excitation functions prove to be very similar to (α, (x − 1)n) reactions at E α ≈23E Li The results present experimental evidence for a particular reaction type indicated in previous experiments: Dissociation of the 6 Li projectile with capture of the beam-velocity α-particle indicating an (α, xn) reaction (“internal break-up”).

The level scheme of 137Nd from (α, χn) reactions and from β-decay of the 112− isomer of 137Pm

Abstract The level scheme of 137 Nd has been investigated by methods of in-beam γ-ray and conversion electron spectroscopy as well as by observing the γ-transitions following the β-decay of 137 Pm . We measured γ-ray and conversion electron singles spectra, γγ coincidences and angular distributions of prompt γ-rays and conversion electrons. The experimental data result in a detailed level scheme of 137 Nd and allow the assignment of spin and parity to the β-decaying level in 137 Pm , i.e. I π = 11 2 − . Members of a disturbed rotational band based on the 11 2 − isomeric state of 137 Nd and populated by prompt γ-transitions (high spin levels) as well as by the β-transitions of 137 Pm (low spin levels) are identified. The negative parity levels are discussed in a particle-plus-rotator model with Coriolis coupling. Though the analysis results in evidence for a weak prolate deformation of 137m Nd , a quantitative description of the observed level scheme is not achieved. There are features which suggest that a γ-deformation of the core has to be taken into account.

The optical potential for 6Li-6Li elastic scattering at 156 MeV

Abstract Elastic scattering of 6 Li from 6 Li has been studied for a beam energy of 156 MeV. The experimental differential cross sections have been analysed on the basis of the optical model using various phenomenological forms. The spin-orbit interaction proves to be less significant. A semimicroscopic double-folding cluster model which generates the real part of the optical potential by an antisymmetrized dα cluster wave function of 6 Li and αα, dd and dα interactions is well able to describe the experimental data.