K. P. Lieb

Lifetime measurements of states in 41Ca and 41K

Abstract Measurements of the γ-ray decay of states in 41Ca and 41K populated in the reactions 27Al(16O, pn) and 27Al(16O, 2p) have been performed. Using the recoil distance Doppler shift method, mean lifetimes were determined for states in 41 Ca at 3370 keV (28 ± 5 ps ), 3830 keV (4.4 ± 0.3 ns ) and 3915 keV (2.6 ± 0.8 ps ), and in 41 K at 2528 keV (230 ± 12 ps ), 2761 keV (1.3. +1.1 −0.6 ps ), 2774 keV (74 ± 8 ps ) and 4983 keV (101 ± 5 ps ) . The 3370 and 3830 keV states in 41Ca are suggested to be J π = 11 2 + and 15 2 + , respectively, having predominantly 2p–1h configurations. These suggestions contradict a recent interpretation of these states as being members of a strongly deformed K = 3 2 − rotational band.

Study of high spin states in 78Kr

Abstract High spin states in 78Kr have been excited in oxygen, fluorine and carbon induced reactions on 65Cu, 64Ni and 68Zn targets. On the basis of γ-γ coincidences, angular distributions and excitation functions, the extension of the level scheme of 78Kr is proposed; four bands connected by stretched E2 transitions have been identified. The lifetimes of some twenty levels have been determined by the recoil distance Doppler shift and Doppler shift attenuation method. The β-decay half-lives of the 103 keV isomeric state and ground state of 78Rb have been remeasured. Very good agreement of the level scheme along the experimental E2 and E1 transition strengths with the interacting boson model IBA-1 and IBA-2 has been established.

Reorientation effect measurements of even mercury isotopes

Reorientation effect and multiple Coulomb excitation measurements have been performed for198, 200, 202, 1204Hg. By measuring particle spectra after Coulomb excitation of an enriched198Hg target with4He and16O beams, a positive quadrupole moment of Q2 = 0.66±0.18 eb (for negative interference) or Q2=0.80±0.18 eb (for positive interference) andB(E2,0→2)=0.991±0.006 e2b2 were obtained. All otherB(E2) values and quadrupole moments were determined relative to these numbers from preciseγ-ray yields obtained from Coulomb excitation of a frozennatHg target with4He and16O projectiles. Oblate shapes of all Hg isotopes were found. The data have been interpreted in terms of triaxial rotation and anharmonic vibrations.

Gamma radiation following heavy ion reactions

Abstract The gamma radiation produced by bombarding 27 A1 and 28 Si targets with 25–50 MeV 16 O ions was measured in order to study the formation and decay of the highly excited compound nuclei 43 Sc and 44 Ti. The relative population of the evaporation residues is fairly well reproduced by a statistical theory describing the successive emission of 1–3 light fragments. From the measured branching ratio between proton and α-particle emission, the moment of inertia parameter of the level density is found to be close to the rigid body value. The influence of heavy ion optical transmission factors, level density parameters and γ-ray decay widths of continuum states is investigated.

Lifetime measurements in g92 decoupled bands

Abstract Lifetimes of positive-parity states in 71,73 As produced by the reactions 56,58 Fe( 18 O,p2n) 71,73 As have been measured by the Doppler recoil-distance method. The ratios of the measured reduced transition rates to the corresponding ones in the core nuclei 70,72 Ge can be explained by assuming that the coupling of a proton in the 1 2 [440] state increases the deformation of the core.

Statistical model calculations of continuum feeding times in heavy-ion fusion reactions☆

The time development of oxygen-induced compound reactions on 27Al and 58Ni targets at 30–70 MeV beam energy has been calculated in the framework of the statistical model. Feeding times associated with the population of yrast states in the evaporation residues have been estimated. It is shown that the experimental feeding times τ1 < 0.2 ps, when combined with measured evaporation residue cross sections and/or absolute γ-ray yields, put restrictions on the spin dependence of the level density. Furthermore, it has been found that the dipole strength of continuum transitions between high-spin states is of the same order of magnitude as that obtained in radiative neutron capture reactions.

Reorientation effect and multiple coulomb excitation measurements of 134Ba

Abstract Measurements of five E2 matrix elements involving the first four levels in 134 Ba have been performed using Coulomb excitation. A small and negative quadrupole moment of Q 2 + = − 0.34± 0.16 e · b or − 0.13± 0.16 e · b was determined, depending upon the sign of P 4 . It is found that the interacting boson model provides a good description of 134 Ba for either sign of P 4 . This is in contrast to many other models which predict P 4

Band structure of 78Kr

Abstract Lifetimes of fifteen states of the ground-state, octupole and gamma-band in 78Kr have been measured; energies and E2 transition strengths have been interpreted in terms of the neutron-proton boson model.

Oblate shapes of200, 202, 204Hg

Measurements of the reorientation effect for the first excited 2+ states in200, 202, 204Hg were performed by exploiting the dependence of theγ-ray yield on Q2+ for different projectiles. For200Hg, a positive quadrupole moment of Q2=0.96±0.11 eb (for negative interference) or Q2=1.11±0.11 eb (for positive interference) was determined indicating an oblate shape. Small positive Q2 values were also found for202Hg and204Hg. Nine B(E2) values for excitation of the 2+, 2+′ and 4+ states in196–204Hg measured.

A direct determination of the sign of the interference term in the Coulomb excitation of 102Ru

Abstract A direct determination of the sign of the interference term which arises in Coulomb excitation has been performed For the case of 102 Ru, this sign was found to be negative in agreement with the relevant model predictions.