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The Zirconium (Z = 40) isotopic chain has attracted interest for more than four decades. The abrupt lowering of the energy of the first 2 + state and the increase in the transition strength B(E2; 2 1 + → 0 1 +) going from 98 Zr to 100 Zr has been the first example of “quantum phase transition” in nuclear shapes, which has few equivalents in the nuclear chart. Although a multitude of experiments have been performed to measure nuclear properties related to nuclear shapes and collectivity in the region, none of the measured lifetimes were obtained using the Recoil Distance Doppler Shift method in the γ γ -coincidence mode where a gate on the direct feeding transition of the state of interest allows a strict control of systematical errors. This work reports the results of lifetime measurements for the first yrast excited states in 98 - 104 Zr carried out to extract reduced transition probabilities. The new lifetime values in γ γ -coincidence and γ -single mode are compared with the results of former experiments. Recent predictions of the Interacting Boson Model with Configuration Mixing, the Symmetry Conserving Configuration Mixing model based on the Hartree–Fock–Bogoliubov approach and the Monte Carlo Shell Model are presented and compared with the experimental data. [ABSTRACT FROM AUTHOR]

γ -ray spectroscopy of fission fragments is a powerful method for studies of nuclear structure properties. Recent results on the spectroscopy of fission fragments, using the combination of the AGATA γ -ray tracking array and the VAMOS++ large acceptance magnetic spectrometer at GANIL, are reported. A comparison of the performance of the large germanium detector arrays EXOGAM and AGATA illustrates the advances in γ -ray spectroscopy of fission fragments. Selected results are highlighted for prompt γ -ray spectroscopy studies, measurements of short lifetimes of excited states with the Recoil Distance Doppler-Shift method, using both AGATA and VAMOS++ and prompt-delayed γ -ray spectroscopy studies using AGATA, VAMOS++ and EXOGAM. [ABSTRACT FROM AUTHOR]

The γ -ray strength function (γ SF) and nuclear level density (NLD) have been extracted for the first time from inverse kinematic reactions with the Oslo method. This novel technique allows measurements of these properties across a wide range of previously inaccessible nuclei. Proton– γ coincidence events from the d (86 Kr , p γ) 87 Kr reaction were measured at iThemba LABS and the γ SF and NLD in 87 Kr was obtained. The low-energy region of the γ SF is compared to shell-model calculations, which suggest this region to be dominated by M1 strength. The γ SF and NLD are used as input parameters to Hauser–Feshbach calculations to constrain (n , γ) cross sections of nuclei using the TALYS reaction code. These results are compared to 86 Kr (n , γ) data from direct measurements. [ABSTRACT FROM AUTHOR]

The low-lying states in the odd-odd and unstable isotopes 106, 108In have been Coulomb excited from the ground state and the first excited isomeric state at the REX-ISOLDE facility at CERN. With the additional data provided here the $ \pi$ g9/2 -1 ⊗ $ \nu$ d5/2 and $ \pi$ g9/2 -1 ⊗ $ \nu$ g7/2 multiplets have been re-analyzed and are modified compared to previous results. The observed $ \gamma$ -ray de-excitation patterns were interpreted within a shell model calculation based on a realistic effective interaction. The agreement between theory and experiment is satisfactory and the calculations reproduce the observed differences in the excitation pattern of the two isotopes. The calculations exclude a 6+ ground state in 106In . This is in agreement with the conclusions drawn using other techniques. Furthermore, based on the experimental results, it is also concluded that the ordering of the isomeric and ground state in 108In is inverted compared to the shell model prediction. Limits on B( E2) values have been extracted where possible. A previously unknown low-lying state at 367keV in 106In is also reported. [ABSTRACT FROM AUTHOR]

Three low-lying 8+ states have been identified in 192Pb . A newly observed cascade of $ \gamma$ -rays built directly on the 8+ 1 state is compared to the previously identified, weakly rotational band above the 11- $ \pi$ i13/2 , h9/2 isomer in the same nucleus, and to analogous structures in 194Pb . The similarity of all four structures lends support to the suggestion that the 8+ 1 configurations are of a similar oblate deformation to the 11- isomers. The excitation energies of all three 8+ states in 192Pb and 190Pb are compared to systematics. The possibility that one of the 8+ states in 192Pb is associated with a prolate shape is discounted. [ABSTRACT FROM AUTHOR]

The odd- Z isotope 255Lr, its daughter 251Md and grand-daughter 247Es were studied in two experiments performed at GANIL and the University of Jyväskylä. The 255Lr nuclei were produced using the cold fusion-evaporation reaction 209Bi(48Ca, 2n)255Lr at a bombarding energy of 217MeV. The single-particle structure and decay properties were investigated using α, γ and electron spectroscopy. The ground-state spin and parity could be assigned for 255Lr (1/2-) and 251Md (7/2-). States corresponding to the 7/2+[633], 7/2-[514] and 1/2-[521] Nilsson orbitals were observed. Results are compared to experimental data obtained in neighbouring isotopes and to Hartree-Fock-Bogoliubov calculations using the Skyrme interaction SLy4 and a density-dependent pairing interaction. The position of the 1/2-[521] orbital from the spherical 2 f 5/2 shell is discussed. [ABSTRACT FROM AUTHOR]

Lifetimes of excited states in the ground-state bands of 74Kr and 76Kr were measured using the recoil-distance Doppler-shift and the differential decay curve methods. The states were populated in the 40Ca(40Ca, α2 p) and 40Ca(40Ca, 4 p) reactions. Gamma rays were detected with the GASP array which was coupled to the Cologne Plunger device. The results resolve discrepancies between earlier lifetime measurements and a recent Coulomb excitation experiment. Experimental transition rates are compared to theoretical calculations. The results support a strong mixing between prolate and oblate configurations for the low-spin states, and represent an important basis for the interpretation and understanding of the shape coexistence phenomenon in this mass region. [ABSTRACT FROM AUTHOR]

Evidence for the decay of non-yrast states in 254No has been observed for the first time in an experiment performed at the University of Jyväskylä. The experiment employed the JUROGAM array of germanium detectors coupled to the gas-filled recoil separator RITU and the focal-plane spectrometer GREAT. The ground-state rotational band has been tentatively extended up to a spin of 24ℏ and has a smoothly behaving dynamical moment of inertia. It is speculated that the observation of high-energy γ-rays is due to the decay of a K = 3 band-head state. [ABSTRACT FROM AUTHOR]

Over the past few years a great deal of new spectroscopic data has been obtained for transfermium nuclei. Recoil separators, coupled with modern target position and focal-plane spectrometers, allow detailed studies of the structure and decay properties of transfermium nuclei to be peformed. In-beam studies using the recoil-gating and recoil-decay tagging techniques mainly provide information on yrast states, whilst complementary focal-plane decay studies give access to non-yrast and isomeric structures. In-beam studies of nuclei in this region have largely been performed at ANL and JYFL, and decay experiments at GSI, JYFL, GANIL and ANL. The present contribution is focussed on recent developments and experiments carried out by a number of collaborating institutes at JYFL. [ABSTRACT FROM AUTHOR]

A superdeformed band has been observed in theN= 108 isotope190Pb. This is the most neutron-deficient Pb isotope in which superdeformed states have been observed. Several theoretical approaches have predicted thatN= 108 will mark the limit of observable superdeformation in the Pb isotopes. The band, which consists of five (possibly six) transitions, is observed to feed at least one isomeric level in its decay to the ground state. This decay pattern supports a spin assignment of 10? for the lowest observed level. [ABSTRACT FROM AUTHOR]

The collective structures of131Cs have been investigated by in-beam ?-ray spectroscopic techniques following the124Sn (^11B , 4n) reaction at a beam energyElab = 57MeV. The previously established rotational bands, built on pg7/2, pd5/2 and the unique-parity ph11/2 orbitals, have been extended and evolve into new bands involving rotationally aligned ?(h11/2)2 and p(h11/2)2 quasiparticles. In addition, a new multiquasiparticle band based on the pg7/2 ? ?g7/2 ? ?h11/2 configuration has also been observed. Theoretical interpretations for the assigned configurations are discussed in the framework of Total Routhian Surface (TRS) and Tilted Axis Cranking (TAC) model calculations. TAC model calculations predict a decrease in theB(M1) values with increasing rotational frequency for the pg7/2/pd5/2 ? ?(h11/2)2 and ph11/2 ? ?(h11/2)2 bands, thus indicating a magnetic rotation character for these bands. [ABSTRACT FROM AUTHOR]

Superdeformed bands in 88Mo and 89Tc were populated using 40Ca-induced fusion-evaporation reactions on 58Ni at a beam energy of 185MeV. Gamma-rays emitted in the reactions were detected using the Gammasphere spectrometer, in coincidence with charged particles detected by the Microball array. A new superdeformed band was assigned to the nucleus 88Mo, leading to a revisit of earlier configuration assignments for superdeformed structures in this nucleus. In particular, the theoretical interpretation of a pair of identical (isospectral) superdeformed bands in 88Mo/89Tc is discussed. The configurations that are assigned to the four SD bands belonging to 88Mo have properties that are predicted to be significantly affected by pair correlations. [ABSTRACT FROM AUTHOR]

Prompt and delayed gamma-ray spectroscopy of very neutron-deficient bismuth isotopes 187,189Bi has been performed using the recoil decay tagging method. A rotational band has been observed in 189Bi and is interpreted as a complete decoupling of a single proton from the deformed lead core. The results for 187Bi suggest a similar structure and coupling scheme. This study gives the first evidence for a prolate band in a light bismuth nucleus and confirms the prolate character of the low-lying rotational band observed in the core nuclei 188Pb and 186Pb. [ABSTRACT FROM AUTHOR]

A multi-nucleon transfer reaction using an 850 MeV 136Xe beam incident on a 198Pt target was used to populate high-spin states in 184W, 14 nucleons from the target. A 4-quasiparticle isomer with t1/2 =188±38 ns has been observed for the first time and its de-excitation through collective and intrinsic structures studied. The results are compared with predictions of blocked BCS Nilsson calculations. Observation of this metastable state completes the tungsten 4-quasiparticle isomer systematics from A 176 to 186. Mapping out the most yrast 4-quasiparticle isomers in these even-even tungsten isotopes suggests the existence of a highly favoured state in 188W, within reach of current experimental set-ups. [ABSTRACT FROM AUTHOR]

The even-even nucleus 136Nd was studied via in-beam γ-ray spectroscopy using the 16O + 125Te reaction at 100 MeV and the EUROBALL array. One new dipole band was observed. Together with a previously identified dipole band, whose position in the level scheme is revised, the new band forms a doublet structure similar to the recently observed chiral bands in the odd-odd neighboring nuclei. This would be the first case of a chiral doublet in an even-even nucleus. [ABSTRACT FROM AUTHOR]

Lifetimes of states in the yrast superdeformed bands of 163Lu and 164Lu were determined in a Doppler-shift attenuation-method experiment. From fractional Doppler shifts and line shapes, average transition quadrupole moments, Qt = 8.2-0.6 +1.0 b and 7.1-0.6 +0.5 b, were deduced for one of the bands in 163Lu and 164Lu, respectively. These values are much larger than the quadrupole moment of the normal-deformed yrast band in 163Yb, Qt = 4.9-0.4 +1.3 b, that was also determined in this experiment. Comparison to cranking calculations indicates that both superdeformed bands correspond to a local potential energy minimum with a pronounced triaxiality, γ∼ 20°. [ABSTRACT FROM AUTHOR]

Lifetimes for low-lying members of the irregular Δ I = 1 band in 196Pb have been measured by means of the EUROBALL spectrometer using the coincidence recoil distance technique. The 164Dy(36S,4n)196Pb reaction at a beam energy of 168 MeV was used. The data were analyzed with the differential decay-curve method (DDCM). A characteristic drop in the reduced transition probabilities with increasing angular momentum was observed in agreement with predictions by the semiclassical model for the shears mechanism. [ABSTRACT FROM AUTHOR]

The band structures built on the 5- isomeric state ( T1/2 = 3.46 m) in the doubly odd 130Cs nucleus have been established up to I = 24? via the 124Sn(11B, 5n)130Cs reaction. The previously observed bands based on the π h11/2⊗ν h11/2, π g7/2⊗ν h11/2 and π d5/2⊗ν h11/2 configurations and a positive-parity side band with multiple connections to the α = 0 signature partner of the yrast π h11/2⊗ν h11/2 band have been extended to higher spins. A new band based on the π h11/2⊗ν g7/2 configuration is observed. The yrast π h11/2⊗ν h11/2 band exhibits anomalous signature splitting whose magnitude decreases up to spin 15 and then increases without restoring the normal signature splitting. [ABSTRACT FROM AUTHOR]

We report the identification of six new superdeformed (SD) bands in 197,198Pb observed with the EUROBALL IV spectrometer. The results are interpreted in the framework of cranked Hartree-Fock calculations with approximate projection on the particle number by means of the Lipkin-Nogami method. A mixing between quasi-particle excitations and an octupole vibration is suggested in the two SD isotopes. We have estimated the ordering of the neutron valence orbitals and confirm indirectly a N = 118 SD gap. [ABSTRACT FROM AUTHOR]

High-spin states in 202Pb and 203Pb have been investigated by in-beam γ-ray spectroscopy following the reaction 198Pt(9Be,xn). A search for magnetic rotational bands in these isotopes confirmed one of the two bands previously assigned to 202Pb and revealed a new band in this isotope. No evidence for magnetic rotation has been found in 203Pb. [ABSTRACT FROM AUTHOR]

High–spin states in 200Hg have been investigated by in–beam γ–ray spectroscopy following the reaction 198Pt(9Be,α3n). The α–emission channel leading to 200Hg is strongly enhanced which may be explained by an incomplete fusion reaction with pre–equilibrium emission of the α particle. The level scheme is extended to higher spins and new band crossings are observed. The band structures are compared to the lighter Hg isotopes with even mass number. [ABSTRACT FROM AUTHOR]

Magnetic–rotational bands in the nearly spherical nuclei 197Pb and 199Pb and their decay to the normal states have been investigated by in–beam conversion electron spectroscopy following (heavy ion,xn) reactions. The expected M1 multipolarity of the in–band transitions has been confirmed for the strongest bands and the multipolarity of several transitions in the decay of the bands has been determined. [ABSTRACT FROM AUTHOR]

Three mini-orange conversion–electron spectrometers and four Euroball Ge Cluster detectors have been used for γ–e- coincidence spectroscopy of superdeformed 135Nd. 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. [ABSTRACT FROM AUTHOR]

Lifetimes of excited states in 107Tc, 109Rh, 111Rh, and 113Rh were measured at GANIL using the Recoil-Distance Doppler Shift method. The neutron-rich nuclei were produced in fission reactions in inverse kinematics with a 238U beam impinging on a 9Be target. Fission fragments were identified event-by-event in the ray-tracing spectrometer VAMOS++ and correlated with prompt γ rays observed around the target position with the EXOGAM Ge detector array. Several lifetimes were obtained for states in the positive-parity yrast bands in the four nuclei and compared to triaxial particle-rotor calculations. The results clarify the configuration for the strongest positive-parity band in 107Tc and suggest a gradual increase of triaxial deformation with atomic number Z, reaching almost maximum triaxiality for the neutron-rich Rh nuclei. [ABSTRACT FROM AUTHOR]