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Results of a 208 Pb (γ,γ′) experiment are presented aiming at an identification of the 2 + member of the long-sought two-octupole phonon multiplet. Four E2 excitations have been observed below 6.5 MeV excitation energy, two of them for the first time. However, in contrast to new results of calculations within the quasiparticle–phonon nuclear model (QPM), no obvious candidate for the two-octupole phonon vibration could be found in the present study. We discuss the J π =2 + states detected in this as well as previous experiments with respect to their possible two-octupole phonon structure.

A nuclear resonance fluorescence experiment on 88Sr has been performed with bremsstrahlung of 6.7 MeV endpoint energy. The γ-ray linear polarisation has been measured with a EUROBALL CLUSTER detector used as a Compton polarimeter. The results indicate positive parity for the J= 1 state at 4.742 MeV in 88Sr, in contrast to the previous interpretation as a 1− two-phonon (2+1⊗ 3−1) state and in conflict with the predictions of the quasiparticle-phonon model. On the basis of such calculations the 1+ state at 3.486 MeV may be considered as the 1+1 one-phonon state and the very strong 1+1→ 0+1 deexcitation as proton spin-flip 2p1/2→ 2p3/2 transition.

In the neutron deficient isotopes 104,105In lifetimes of high spin states in the range from 0.5 ps to 600 ps have been measured in a coincidence recoil distance Doppler shift (RDDS) experiment. By combining the Doppler shift attenuation (DSA) and RDDS methods at few μm flight distances, the problem of delayed feeding has been avoided and very short lifetimes in the range 0.5–0.8 ps have been determined. Shell model calculations with strong restrictions for the neutron orbitals reveal good agreement with experimental level energies and still fair agreement for most measured B(M1) and B(E2) values.

High spin states in ${}^{104}\mathrm{Sn}$ were identified in the reaction ${}^{58}\mathrm{Ni}{(}^{50}\mathrm{Cr}$, $2p2n)$ at 200 and 205 MeV beam energies. The $\ensuremath{\gamma}$-ray energies, intensities, multipolarities, and lifetimes of high spin states were measured with the GASP spectrometer array in combination with a plunger apparatus by means of the recoil distance Doppler shift method. The deduced level scheme and transition probabilities are compared to the results of large-scale shell model calculations using three independent two-body interactions. The agreement of the level energies is satisfactory, except for a cascade of dipole transitions at high spins. The general good agreement found for $E2$ transition strengths implies a large effective neutron polarization charge. The shell-model calculations do not account for the measured enhanced $E3$ transitions for which a core excited octupole phonon admixture is indicated.

The lifetimes of three low-lying states in the superdeformed (SD) yrast band of {sup 194}Hg were measured applying the recoil-distance Doppler-shift method. As the deduced transition quadrupole moments Q{sub t} are equal within the experimental uncertainties to those extracted from a Doppler-shift attenuation method (DSAM) measurement for the high-lying states of the band, the assumption that the decay out of SD bands does not strongly affect the structure of the corresponding states is corroborated. By a simple mixing model, the decay can be described assuming a very small admixture of normal-deformed (ND) states to the decaying SD states. The deduced ND mixing amplitudes for the yrast SD bands in {sup 192,194}Hg and {sup 194}Pb are presented along with average transition quadrupole moments for the lower parts of the excited SD bands in {sup 194}Hg. {copyright} {ital 1997} {ital The American Physical Society}

Neutron particle-hole states in the doubly magic nucleus 208 Pb were investigated using a Euroball Cluster detector and five usual HPGe detectors at the Osiris cube spectrometer in Cologne. 126 γ-ray transitions with energies up to 7.2 MeV could be detected 14 for those for the first time. The states were excited with the 208 Pb( p , p ' γ ) 208 Pb reaction via isobaric analogue resonances in 209 Bi at E p = 16.5, 17, 17.45, 17.5 and 18.5 MeV and though the subcoulomb 207 Pb( d , pγ ) 208 Pb reaction at E d = 10 MeV. For most of the excited states assignments for the particle and/or the hole component of the configuration could be made, 22 of these are new.

An in-beam experiment with the subcoulomb reaction 209Bi(3He, d*γγ)210Po at 20.5 MeV was performed with two Euroball Cluster detectors in Cologne. It closed the gap between the low energy levels of the level-scheme and the high energy levels found in 209Bi(3He, d)210Po and 208Pb(4He, t)210Po particle experiments. New branchings have been found and the (3He, d*γγ) reaction below the coulomb-barrier has been used successfully.

The mean lifetimes of the ${25/2}^{+}$, ${21/2}^{+}$, and ${17/2}^{+}$ states in the highly deformed (HD) band of $^{133}\mathrm{Nd}$, excited via the reaction $^{104}\mathrm{Pd}$($^{32}\mathrm{S}$,2$\mathit{pn}$)$^{133}\mathrm{Nd}$, have been measured using a recoil distance Doppler-shift method. The decay out of the HD band occurs as a result of an admixture of normally deformed (ND) components into the HD states' wave function. The consistency in the mixing amplitude was assessed from the measured lifetimes, branching ratios, and quadrupole moments of the HD and the ND bands. This analysis unequivocally confirms the earlier approach to explain the decay-out mechanism.

Lifetimes of 20 high spin states in Ag-101 in the range between 0.2 and 200 ps have been measuredand interpreted within the boson fermion plus broken pair model.

Using the reaction ${}^{58}\mathrm{Ni}{(}^{50}\mathrm{Cr},\ensuremath{\alpha}$ $2p)$ and the coincidence recoil distance Doppler shift technique, we determined picosecond lifetimes of high-spin states in ${}^{102}\mathrm{Cd}.$ The positive-parity yrast and yrare cascades evidence the competition and interplay of the two proton holes in the ${g}_{9/2}$ orbit and four neutrons in the ${d}_{5/2},$ ${g}_{7/2},$ and ${h}_{11/2}$ orbits, outside the $Z=N=50$ ${}^{100}\mathrm{Sn}$ core. At positive parity, this interplay leads to multiplets of states in the spin range ${6}^{+}--{10}^{+},$ some of which are connected by very weak $E2$ transitions. At higher spins, spin-aligned proton holes and neutrons lead to magnetic rotation. Energies and transition strengths when compared with the predictions of several shell model calculations reveal the high sensitivity on the model parameters.

For the investigation of the collectivity and the structure of the intruder bands with positive and negative parity in 114 Sn, coincidence lifetime measurements using the recoil distance Doppler shift (RDDS) and the Doppler-shift attenuation (DSA) methods were performed at the GASP spectrometer at the INFN-Laboratori in Legnaro. Excited nuclear states were populated with the reaction 100 Mo( 18 O,4n) 114 Sn. For analysis the differential decay curve method was used in the γγ -coincidence mode. In total 31 lifetimes could be obtained, belonging to 11 and 13 states in the positive- and negative-parity intruder bands, respectively, and to 7 spherical states. This work enhances our knowledge of low-lying collectivity among the Sn isotopes near the mid-shell region.

Picosecond lifetimes in ${}^{129,130}\mathrm{Ba}$ were determined using the recoil distance technique with a plunger device coupled to an array of EUROBALL-cluster-detectors for the first time. The differential decay curve method in coincidence mode was employed to derive lifetimes for six states in ${}^{129}\mathrm{Ba}$ and twelve states in ${}^{130}\mathrm{Ba}.$ The resulting $B(E2)$ values are compared with triaxial rotor plus particle calculations for ${}^{129}\mathrm{Ba}$ and, in ${}^{130}\mathrm{Ba},$ to the predictions of the general collective model, the interacting boson model, as well as to the symmetric and asymmetric rotor models. In ${}^{130}\mathrm{Ba},$ the transitional quadrupole moment in the ground state band is remarkably constant before and after the backbend. With this data the two-quasiparticle negative parity band in ${}^{130}\mathrm{Ba}$ was confirmed to be based on a $\ensuremath{\pi}{(h}_{11/2}\ensuremath{\bigotimes}{d}_{5/2}{/g}_{7/2})$ configuration.

The electric dipole strength distributions below threshold in stable even-mass Pb isotopes have been extracted from photon scattering experiments at the superconducting Darmstadt electron linear accelerator S-DALINAC. Between 4 and 6.5 MeV excitation energy a resonance-like clustering of strength is observed. A strong evolution of a fragmentation of the dipole strength with opening the neutron shell is found. The fine structure of the strength is compared to microscopic quasiparticle-phonon model calculations that quantitatively reproduce the data quite well and explain the fragmentation of the dipole strength. Models suggesting the oscillation of excess neutrons with respect to an N ≃ Z core as a possible origin of low-lying E1 strength are critically examined.

The electromagnetic dipole response of ${}^{138}\mathrm{Ba}$ was measured up to 6.7 MeV excitation energy in a photon scattering experiment. Two Euroball Cluster detectors were used to detect the scattered photons under 94 and 132 degrees. The Cluster at 94 degrees served as a Compton polarimeter. The total observed dipole cross section is in good agreement with previous tagged photon data, but in the present experiment the transition strength and the electric character of most of the transitions has been determined on a state-by-state basis. The data show a concentration of $E1$ strength around 6 MeV. For one of the strongest excitations $M1$ character is suggested. The results of model calculations using the quasiparticle phonon model (QPM) agree with the observed electric dipole strength distribution.

The mean life of the 12+ level at 4195 keV in146Sm has been measured with the Recoil Distance method. The reduced strength of the E3 decay 12+→9−, about 60 W.u., confirms the collectivedouble-octupole character of the 12+ level.

We report on a nuclear resonance fluorescence experiment on the semi-magic odd-mass fp -shell nucleus 51 V. The detected dipole strength distribution is discussed on the basis of modern shell-model calculations employing a model space allowing for excitations of protons and neutrons from the 1 f 7/2 to the (2 p 1/2 ,2 p 3/2 ,1 f 5/2 ) shells. The calculations indicate that the main body of transitions is of magnetic dipole type, and they are capable of reproducing the observed distribution well. Possible electric dipole and quadrupole contributions are also discussed.