Level lifetimes for the candidate chiral doublet bands of 80Br were extracted by means of the Doppler-shift attenuation method. The absolute transition probabilities derived from the lifetimes agree well with the M1 and E2 chiral electromagnetic selection rules, and are well reproduced by the triaxial particle rotor model calculations. Such good agreements among the experimental data, selection rules of chiral doublet bands and theoretical calculations are rare and outstanding in researches of nuclear chirality. Besides odd-odd Cs isotopes, odd-odd Br isotopes in the A≈ 80 mass region represent another territory that exhibits the ideal selection rules expected for chiral doublet bands.

Excited states of the nucleus Br-79 were investigated via the reaction Ge-76(Li-7,4n) at a beam energy of 35 MeV. Coincidence data of emitted gamma rays were measured with an arrangement of six EUROBALL CLUSTER detectors. The E2 bands built on the 9/2(+) and 3/2(-) states were extended up to J=37/2 at Eapproximate to8.8 MeV. The M1 band starting with a 15/2(-) state at 2.6 MeV was observed up to J=(29/2) at E=6.4 MeV. Crossover E2 transitions within this band were observed for the first time. Mean lifetimes of 17 levels were deduced using the Doppler-shift-attenuation method. The M1 band can be described within the tilted-axis-cranking model on the basis of the tilted three-quasiparticle configuration pi(g(9/2)) nu(g(9/2)) nu(fp) which has a triaxial shape. This band appears as a mixed case including contributions of both magnetic and collective rotation.

Picosecond lifetimes in Ba-129.130 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 Ba-129 and twelve states in Ba-130. The resulting B(E2) Values are compared with triaxial rotor plus particle calculations for Ba-129 and, in Ba-130, to the predictions of the general collective model, the interacting boson model, as well as to the symmetric and asymmetric rotor models. In Ba-130, the transitional quadrupole moment in the ground state hand is remarkably constant before and after the backbend. With this data the two-quasiparticle negative parity band in Ba-130 was confirmed to be based on a pi(h(11/2)xd(5/2)/g(7/2)) configuration.

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.

Magnetic dipole moments of excited states in Zr-84 and the N=46 isotones Zr-86 and Nb-87 were measured. The recoil distance transient field method, which is a coincidence technique combining the recoil distance and the transient field methods, was applied. The measurement was performed such that it was sensitive only to those excited states which were populated a few picoseconds after the nuclear reaction. The influence of unobserved continuum feeding on the measured precession angles can thus be neglected. The results are compared with the values obtained using other experimental techniques and with shell model calculations. [S0556-2813(99)01704-5].

Magnetic dipole moments of excited states in ${}^{84}\mathrm{Zr}$ and the $N=46$ isotones ${}^{86}\mathrm{Zr}$ and ${}^{87}$Nb were measured. The recoil distance transient field method, which is a coincidence technique combining the recoil distance and the transient field methods, was applied. The measurement was performed such that it was sensitive only to those excited states which were populated a few picoseconds after the nuclear reaction. The influence of unobserved continuum feeding on the measured precession angles can thus be neglected. The results are compared with the values obtained using other experimental techniques and with shell model calculations.

The recoil-distance Doppler-shift technique was employed to determine lifetimes of high-spin states in the semimagic nucleus Ru-94. The nuclei were populated using the reaction Ni-58(Ca-40,4p) at a beam energy of 145 MeV, and the gamma radiation from their decay was detected in six EUROBALL cluster detectors. A total of 23 reduced transition probabilities and limits for fifteen further transitions were extracted and compared to large-scale shell model calculations, considering different configuration spaces and residual interactions. The information deduced on transition strengths turned out to be essential for the correct assignment of the calculated to the experimental excited states. The results indicate that the 13(2)(-) (6919 keV), 14(1)(-) (7970 keV), and the 15(1)(-) (8133 keV) levels have pure proton pi(f(5/2))(-1) pi(g(9/2))(5) configurations, whereas all other excited states above 6.3 MeV are built from a neutron g(9/2)-->d(5/2) excitation across the N = 50 shell closure, coupled to up to six valence protons. Strong M1 transitions were found in a stretched dipole cascade within the sequence of neutron core-excited states at positive parity, while the strengths of the transitions between core-excited and pure proton states were proven to be small, similar as in Rh-95.

A first level scheme of ${}^{68}\mathrm{Se}$ with five states up to 4.2 MeV excitation energy and tentative spins ${6}^{+}$ and ${7}^{\ensuremath{-}}$ has been established from \ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\gamma} coincidences measured with six EUROBALL Cluster detectors in close geometry. The level scheme is interpreted in comparison with neutron deficient nuclei of the $A\ensuremath{\approx}70$ region and cranking model calculations. In a similar experiment a triple coincidence between the ${}^{72}\mathrm{Kr}$ transitions 710, 611, and 792 keV has been proven.

The large oblate deformation of the69Seg9=2 band was proven by the DSA analysis of the 13/2+ →11/2+ 403 keV transition measured via32S(40Ca, 2pn)69Se at 125 MeV beam energy with six escape suppressed EUROBALL Cluster detectors at ±44°. Applying the model of a rigid axial-symmetric rotor the determined lifetime resulted in ∣β2∣ ɛ [0.24,0.85].

Lifetimes of high-spin states in the N = 50 nucleus 95Rh were measured using the recoil-distance Doppler-shift technique. The nuclei were produced via the reaction 58Ni(40Ca,3p) at 145 MeV beam energy and the γ radiation was detected in six EUROBALL cluster detectors. Reduced transition probabilities for seventeen γ transitions and limits for nine further transitions were extracted and compared with the predictions of the spherical shell model based on the extended configuration space, (0f52, 1p32, 1p12, 0g92) for protons and (0g92, 1d52) for neutrons relative to a hypothetical 68Ni core. The results indicate that all observed states with 272 ⩽ I ⩽ 392 are built from a neutron g92 → d52 excitation across the N = 50 shell closure, coupled to up to five valence protons in different configurations. Evidence of stretched dipole cascades having large M1 strengths was found and explained by spin recoupling within the ν(g92)−1ν(d52) neutron part of the wavefunctions.

The recoil distance transient field technique in coincidence mode has been used to measure the magnetic moments of the 21/2(+) and 29/2(-) yrast states in Nb-87. This method in conjunction with the use of five highly efficient EUROBALL cluster detectors has for the first time allowed the direct determination of individual g factors of picosecond high-spin states populated in heavy-ion compound-nucleus reactions. The value g(29/2(-)) = +0.56(16) indicates that the five-quasiparticle band consists of both an aligned g(9/2) proton and a g(9/2) neutron pair besides the odd p(1/2) proton.

MassA ≈ 90 nuclei with several valence nucleons outside the doublymagic100Sn core are an ideal testing ground for the validity of the spherical shell model. Electromagnetic decay properties as well as magnetic dipole moments of excited states are the key quantities revealing the structure of the wave functions and themechanisms responsible for strong dipole sequences. The present article discusses by means of two examples the advantages of employing the most recent developments both concerning detector technology and experimental methods.

: Three mini-orange conversion–electron spectrometers and four Euroball Ge Cluster detectors have been used for γ–e - coincidence spectroscopy of superdeformed 135 Nd. Transitions within the superdeformed band are shown to have the expected E2 multipolarity. The 766.5–keV transition which links the band to a positive-parity state has a conversion coefficient consistent with M1 multipolarity. Consequently, positive parity is deduced for the superdeformed band. No evidence for E0 transitions was found.

High-spin states in (RU)-R-92 were populated via the reaction Ni-58(Ca-40, alpha 2p) at 145 MeV beam energy. Using six EUROBALL cluster detectors we measured lifetimes by means of the recoil distance Doppler shift method and are able to propose several significant changes in the published level scheme of (RU)-R-92. While the observed spin dependence of M1- and moderately enhanced E2-strengths is well reproduced by the shell model in the parametrization by Gross and Frenkel, the use of a surface delta residual force leads to less satisfactory results.

We have investigated the structure of the superdeformed band in 135Nd using conversion-electron spectroscopy. The transitions within the superdeformed band show conversion coefficients which are consistent with an E2 multipolarity. From the conversion coefficients of transitions linking this band with known low-lying states its positive parity was established. Hence, a direct determination of the parity of a high-spin superdeformed band could be performed for the first time.

Coulomb excitation of secondary beams (5 less than or equal to Z less than or equal to 20) at energies around 250 A . MeV was explored at GSI. For low-lying states, gamma-ray spectroscopy was utilized, while high-lying excitations were investigated by means of invariant-mass spectroscopy.

We report on a measurement of the lifetime of the 1414 keV state in232Th by the Doppler-shift recoil-distance method. This 4+ state shows all characteristics of a nearly-harmonic two-phononγ-vibrational excitation. The result for the B(E2) value obtained from the lifetime,τ=3.2 ± 0.7 ps, is in agreement with an earlier estimate of the collectivity from Coulomb-excitation yields and supports the interpretation of the 1414 keV state as a two-phononγ-vibrational excitation.

The decay of e+e− at rest into four photons has been measured in a 20-day experiment at the Heidelberg-Darmstadt Crystal Ball. From a total of 4.9 × 1010 annihilations observed, 406 4gg events with an estimated background contamination of less than 5% have been isolated. Energy and angular distributions are found to agree excellently with simulations based on QED. Using a parallel measurement of 3γ-annihilation for a reduction of systematic uncertainties, the branching ratio Γ4γ/Γ2γ is obtained to be (1.50±0.07(stat.) ±0.09(syst.)) × 10−6, in agreement with lowest-order QED.