New yrast excited states of the N = 84 nucleus 142Ce observed in deep inelastic reactions

Excited states of ¹⁴²Ce, populated in deep inelastic reactions of ⁸²Se projectiles bombarding ¹³⁹La target, have been studied up to medium spins using in-beam γ spectroscopy techniques. Three new levels have been identified at 2625, 2995, 3834 keV, and assigned as 8⁺, 9^(-) and 11^(-), respectively. These new yrast states follow closely the level systematics of the even mass N = 84 isotones. Their strctures have been discussed with the help of empirical shell model calculations. Received: 2 November 2001 / Accepted: 15 January 2002     

Intruder states in even-even neutron-rich Pd isotopes

The decays of ¹¹²Rh ^g and ¹¹²Rh ^m obtained as on-line mass separated fission products have been investigated by standard β and γ spectroscopic techniques and γ-γ angular correlations. Low-lying 0⁺ and 2⁺ states are identified in the daughter nucleus ¹¹²Pd. Systematics suggests the existence of an intruder band which is the lowest in ¹¹⁰Pd, i.e. two neutrons before the midshell. Received:13 March 1998     

Beta Decay of 111Tc to 111Ru

The β-decay of the very neutron-rich ¹¹¹Tc nucleus has been observed. A partial decay scheme of ¹¹¹Ru is presented, complementing the high-spin levels earlier reported in spontaneous fission work. Received: 15 January 1998     

Terminating high-spin bands in 101Rh

High spin states of ¹⁰¹Rh have been populated using the reaction ⁷⁰Zn+³⁶S at 130 MeV. γ-rays were detected with the EUROGAM2 array. New high-spin bands have been observed in this nucleus up to 45/2⁻, 57/2⁻ and 65/2⁺ states. They have been interpreted using the Nilsson-Strutinsky cranking formalism as terminating configurations. Two of the bands were observed up to the predicted terminating states which are built up from g_9/2 protons as well as d_5/2, g_7/2 and h_11/2 neutrons relative to a ⁹⁰Zr core. Received: 30 October 1998     

Shape coexistence near the double-midshell nucleus 111Rh

The decay of ¹¹¹Ru obtained from fast on-line chemical and mass separation has been investigated by β-γ-t and γ-γ coincidence techniques. Earlier spin and parity assignments of ¹¹¹Rh levels based on extrapolations of level systematics are confirmed. In particular, the K=1/2 intruder band is supported by the hindrance of E2 transitions between deformed and spherical states and enhancement of intraband E2 transitions. The excitation energies of intruder band members in Rh isotopes show a minimum at ¹⁰⁹Rh₆₄, with two neutrons less than ¹¹¹Rh at the N=66 midshell. This trend, which differs from the one in the higher-Z neighbouring elements Ag and Cd with minima at N=66, follows the evolution of deformation observed in the lower-Z elements Ru and Mo. Received: 25 June 1997 / Revised version: 10 September 1997     

Lifetime measurement of the ((11/2)−) isomer in 125Cs

A new rotational band has been observed in ¹⁶⁷Lu by ¹⁵²Sm (¹⁹F,4n)reaction at the HI-13 tandem accelerator of CIAE in Beijing. The high spin transition energies of the new band are almost identical to the triaxial superdeformed bands recently discovered in ¹⁶³Lu and ¹⁶⁵Lu. This new band is predicted as a triaxial superdeformed band by total routhian surface calculations. Received: 6 October 1997     

High-spin multiparticle-hole excitations in 148Eu

Studies by means of 155 MeV ²⁷Al bombardment on a ¹³⁰Te target revealed in ¹⁴⁸Eu high-spin structures up to spin 31?, in addition to a cascade extended to the 11088.1 keV excitation. The observed levels are tentatively assigned as complex multiparticle-hole proton and neutron configurations. Received: 15 December 2000 / Accepted: 29 January 2001     

New high-spin microsecond isomers in 131Sb

In this work we have identified and studied the decay of two new microsecond isomers 19/2^- and 23/2⁺ in ¹³¹Sb. This neutron-rich nucleus was produced by thermal neutron-induced fission of ²⁴¹Pu. The detection is based on time correlation between fission fragments selected by the LOHENGRIN spectrometer at ILL (Grenoble) and the γ-rays or conversion electrons from isomers. These new data on high-spin states complete the level scheme previously obtained from β-decay. A large fraction of the members of the πg _7/2ν(h _11/2 ^-1 d _3/2 ^-1) and πg _7/2νh _11/2 ^-2 multiplets are now known and were compared with a multi-particle shell model calculation. Received: 7 June 2000 / Accepted: 19 September 2000     

New states in heavy Cd isotopes and evidence for weakening of the N = 82 shell structure

A chemically selective laser ion source has been used in a β-decay study of heavy Ag isotopes into even-even Cd nuclides. Gamma-spectroscopic techniques in time-resolving event-by-event and multiscaling modes have permitted the identification of the first 2⁺ and 4⁺ levels in ¹²⁶Cd₇₈, ¹²⁸Cd₈₀, and tentatively the 2⁺ state in ¹³⁰Cd₈₂. From a comparison of these new states in ₄₈Cd with the E(2⁺) and E(4⁺)/E(2⁺) level systematics of ₄₆Pd and ₅₂Te isotopes and several recent model predictions, possible evidence for a weakening of the spherical N = 82 neutron-shell below double-magic ¹³²Sn is obtained. Received: 13 July 2000 / Accepted: 12 October 2000     

Three-valence-particle fission product 51 135Sb84

By analysis of fission product γ-ray data measured at Eurogam II using a ₂₄₈Cm source, yrast levels up to about 2 MeV in the N=84 three-particle nucleus ₁₃₅Sb have been identified. These levels are interpreted as π g^7/2ν f^7/2 ₂ and π g^7/2ν f^7/2h^9/2 states with the help of shell model calculations using empirical nucleon-nucleon interactions. Received: 30 July 1998     

Configuration assignments and decay of 126La high-spin bands

High spin states of ¹²⁶La have been populated using the reaction ¹¹⁶Sn+¹⁴N at 68 MeV. γ-rays and conversion electrons were detected with the GAREL array. Multipolarities of the lowest-lying in-band dipole transitions have been determined from the deduced internal conversion coefficients. Experimental B(M1)/B(E2) ratios have been derived for the bands and compared with calculated values using the D?nau-Frauendorf geometrical model. Configurations are proposed for the bands comparing them with cranked shell model calculations and on the basis of the measured B(M1)/B(E2) ratios. The β-decay of ¹²⁶La has also been revisited. The population of the ¹²⁶Ba levels gives a probable spin value of five for the decaying high-spin ¹²⁶La state with T _1/2≈ 64 s which may indicate a signature inversion in the πh_11/2νh_11/2 band. Received: 12 October 1999     

In-beam study of 145Tb

The high-spin states of ¹⁴⁵Tb have been studied in the ¹¹⁸Sn(³²S, 1p4n) reaction at ³²S energies from 161 to 175 MeV using techniques of in-beam γ-ray spectroscopy. Measurements of γ-ray excitation functions and γ-γ-t coincidences were performed with 12 BGO(AC)HPGe detectors. Based on the measured results of γ-γ coincidences, γ-ray anisotropies and DCO ratios, a level scheme for ¹⁴⁵Tb was established for the first time. The observed excited states show typical irregular pattern in a spherical nucleus, and the low-lying levels have been interpreted qualitatively with a particle-core coupling. Received: 21 September 2001 / Accepted: 9 November 2001     

Multiple octupole excitations in 148Gd

The lifetime and the -decay to the 0⁺ ground state of the lowest 3^- state in ¹⁴⁸Gd has been determined. The reduced strength B(E3, 3^- 0⁺)=41 (6) W.u. agrees well with the theoretical value from empirical shell model calculations and can be directly compared with the 12⁺ 9^- two-octupole-phonon one-octupole-phonon strength obtained in the same Recoil Distance Method lifetime measurement. The results of our search for a three octupole-phonon state built on the state is also reported. Received: 7 March 2000 / Accepted: 12 May 2000     

On the nature of the 17 μs isomer of the <Superscript>133</Superscript>Sb valence nucleus

The decay of the 17 μs isomer of ¹³³Sb was re-investigated experimentally. It was produced by thermal neutron induced fission of ²⁴¹Pu. Its detection is based on time correlation between fission fragments selected by the LOHENGRIN spectrometer at ILL (Grenoble), and the γ-rays, and conversion electrons from the isomer. The interpretation of the level scheme is based on shell model calculations, where empirical two-body matrix elements were employed. The good agreement between theory and experiment suggests that the isomer is the 21/2⁺ member of the 2p-1h πg _7/2ν(f _7/2 h _11/2 ⁻¹) configuration. Received: 20 January 2000 / Revised version: 28 February 2000     

Maximum spin aligned states in 98 47Ag51

New excited states have been observed in the neutron deficient isotope ⁹⁸Ag following the ⁵⁸Ni+⁵⁰Cr →¹⁰⁸Te^* heavy–ion reaction. One of these states may be interpreted as a maximum spin aligned state of the πg_9/2 ⁻³νg_7/2 configuration. Other possible interpretations within the nuclear shell model are discussed as well. Received: 24 October 1997     

Beta decay of neutron-rich 118Rh and the lowest excited states in 118Pd

Beta decay of a refractory isotope ¹¹⁸Rh produced in symmetric fission and mass separated by the ion guide technique has been applied for the study of low-lying excited states of ¹¹⁸Pd. The yrast band in ¹¹⁸Pd has been observed up to a 6⁺ state and the lowest states of the asymmetric γ-band have been identified. The measured half-life of ¹¹⁸Rh is (300±60)ms. The systematics of the excited states in neutron-rich Pd-isotopes implies the saturation towards an O(6) symmetry at N = 70. Received: 19 June 2000 / Accepted: 1 August 2000     

Quadrupole moment measurement of the highly deformed πg 9/2⊗νh 11/2 band in 130Pr

The quadrupole moment for the πg _9/2⊗νh _11/2 band in the ^130>Pr nucleus has been measured using the Doppler-shift attenuation method. A centroid shift analysis was carried out and a value of Q₀=6.1±0.4 eb, corresponding to an axial prolate deformation of β₂=0.35(3), has been determined. This is the first direct experimental confirmation of the deformation-driving character of the πg _9/2 orbital in an odd-odd nucleus in the A≃135 superdeformed region. Received: 23 April 1998     

Lifetimes and configuration mixing in 110Cd

Lifetimes of excited states in ¹¹⁰Cd have been measured by the Doppler shift attenuation method in the reaction (α,2nγ) at E _α= 25 MeV. Lifetime values for 8 states and lifetime limits for 3 states were obtained. The band structures of ¹¹⁰Cd have been interpreted in terms of a modified version of the interacting boson model (IBM + 2 q.p.). The calculations explain well the excitation energies and electromagnetic transition probabilities up to J ^π= 16⁺, except for the 10⁺ ₁ state. The structural features are discussed in terms of collective and two quasiparticle excitations. Received: 20 March 1999 / Revised version: 28 May 1999     

First decay scheme of 113Tc and identification of 113Ru m

Very neutron–rich fission products of the mass chain A=113 obtained from the IGISOL on–line mass separator have been investigated by γγ coincidence techniques and γ-spectra multiscaling. Gamma–rays following β–decay of ¹¹³Tc have been observed for the first time and a new 0.5 s isomeric state has been found in ¹¹³Ru. Received: 10 February 1998     

Decay of the neutron-rich isotope 113Ru to 113Rh

The decay of neutron-rich isotope ¹¹³Ru obtained as on-line mass separated product of proton-induced fission has been investigated by γγ coincidence and spectrum multiscaling measurements. Decay schemes for both low- and high-spin isomers of ¹¹³Ru have been constructed. The level scheme of ¹¹³Rh is considerably extended. Systematics of the lowest-lying rhodium levels is smooth. The picture of shape coexistence established for neutron-rich Rh isotopes near-neutron midshell is confirmed with the observation of a K = 1/2 deformed band, with its 3/2⁺ state at 600 keV being the lowest-lying level and of probable 7/2⁺ and 5/2⁺ band members. A large fraction of β feeding is found to populate high-lying levels in ¹¹³Rh. The GT strength in ¹¹³Ru^m decay is significantly larger than for the decay of ¹¹³Ru_g and of lighter rhodium isotopes. Received: 18 January 2001 / Accepted: 14 January 2002