Favoured superdeformed states in 89Tc

A superdeformed band consisting of a cascade of ten γ-ray transitions has been identified and assigned to the nucleus ⁸⁹Tc, close to the proton dripline. The quadrupole moment of the band (Q _t= 6.7^+3.0 _−2.3 eb, as measured by the Residual Doppler Shift Method) as well as a large dynamic moment of inertia point to a highly elongated shape. With a relative population of approximately 15% of the γ-ray flux in the ⁸⁹Tc exit channel, the band is among the most intense superdeformed bands observed to date. Received: 6 July 1999     

First identification of excited states in 59Zn

Excited states in ⁵⁹Zn were observed for the first time following the fusion-evaporation reaction ²⁴Mg + ⁴⁰Ca at a beam energy of 60 MeV. The GASP array in conjunction with the ISIS Silicon ball and the NeutronRing allowed for the detection of γ-rays in coincidence with evaporated light particles. The mirror symmetry of ⁵⁹Zn and ⁵⁹Cu is discussed. Received: 28 May 2002 / Accepted: 10 July 2002 / Published online: 3 December 2002 RID="a" ID="a"Present address: Oliver Lodge Laboratory, University of Liverpool, P.O. Box 147, Liverpool, L69 7ZE, United Kingdom; e-mail: ca@ns.ph.liv.ac.uk. RID="b" ID="b"Present address: Physik-Departament, Technische Universit?t München, D-85748 Garching, Germany. Communicated by W. Henning     

Decay of 83Sr and level structure of 83Rb

The excited states of the ⁸³Rb nucleus were investigated in radioactive decay of ⁸³Sr. The level scheme was established and for a number of levels spin-parity assignments are suggested on the basis of log ft values and γ-branching ratios. Combining with the high-spin states observed by the in-beam γ-ray spectroscopy of a previous decay work, the structure of the excited states of ⁸³Rb is discussed in the framework of the projected shell model. Received: 17 November 1999 / Accepted: 11 December 2000     

Coulomb energy differences between isobaric analogue states in 70Br and 70Se

Gamma ray transitions de-exciting states in the N = Z nucleus ⁷⁰Br have been identified for the first time using the GASP and EUROBALL arrays coupled with ancillary detectors. The level scheme of ⁷⁰Br has been established by means of particle-gated γ-γ and γ-γ-γ coincidences. The Coulomb energy differences between isobaric analogue states in ⁷⁰Br and ⁷⁰Se show a deviation from the expected behaviour which could be related to dripline effects. Received: 18 July 2001 / Accepted: 25 September 2001     

High-spin states in 160Lu

High-spin states of ¹⁶⁰Lu have been studied through the ¹⁴⁴Sm( ¹⁹F, 3n) reaction. The previously known πh _11/2⊗υi _13/2 yrast band is extended from I ^π = 21^- to 25^- and a four quasiparticle band with configuration πh _11/2[523]7/2 ^-⊗υh _9/2[521]3/2 ^-⊗ (υi _13/2)² is reported. Received: 21 May 2001 / Accepted: 19 July 2001     

High-spin states in 166Lu

It is shown that the discrepancy between the results obtained for different neutron energy ranges, when neutron polarizability is derived from the neutron scattering data, can be removed if one assumes that at the fast neutron scattering a strong-interaction long-range potential of Van der Waals (～ r ^?6 ) or Casimir-Polder (～ r ^?7 ) is observed. This strong-interaction long-range potential has possibly some experimental confirmation in the elastic p-p scattering.     

Shell model structures in the N = 46 isotones 86Zr, 87Nb, 88Mo, 89Tc, 90Ru and 91Rh

The known level energies, electromagnetic moments and decay probabilities of high-spin states in the N = 46 isotones ⁸⁶Zr, ⁸⁷Nb, ⁸⁸Mo, ⁸⁹Tc, and ⁹⁰Ru are interpreted within the shell model. The single-particle space was truncated to the p _1/2 and g _9/2 orbits (relative to the ⁸⁸Sr core) and the single-particle energies and empirical two-body matrix elements derived by Gross and Frenkel were used in the calculations. Based on the generally good success of this approach, energies and decay properties of the yrast spectra in ⁹⁰Ru and ⁹¹Rh are predicted. Received: 31 July 2000 / Accepted: 18 December 2000     

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     

New excited superdeformed bands in heavy Pb nuclei: Clue for an octupole softness near the N = 118 gap at large deformation

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. Received: 20 December 2000 / Accepted: 24 January 2001     

High-spin states in the deformed 122Ba nucleus

The even-even nucleus ¹²²Ba was studied via in-beam γ-ray spectroscopy using the ⁴⁰Ca + ⁹²Mo reaction at 190 MeV. Five bands were observed, four more that can be found in the literature. Configurations were assigned to the various bands from the comparison with the neighboring even-even nuclei. Received: 10 July 2001 / Accepted: 10 October 2001     

Level structure of 99Rh at high spins

High spins states in ⁹⁹Rh were populated via the ⁶⁶Zn(³⁷Cl, 2p2n)⁹⁹Rh reaction at an incident beam energy of 130 MeV. Seventeen new transitions have been observed in the present study and the level scheme has now been extended up to a spin of J∼ 25ħ and an excitation energy of about E _x∼ 10 MeV. The observation of a positive parity E2 cascade based on the 9/2⁺ isomeric level is suggestive of collective behaviour in this nucleus up to high spins. Spherical shell model (within restricted model space) and Cranked shell model calculations were performed to obtain an insight into the observed level structure. The new collective band observed up to a spin of J∼ 25ħ is suggested to be based on (πg _9/2 ³) ⊗ (νg _7/2 ²) quasi-particle excitations. Received: 12 July 1999 / Revised version: 14 September 1999     

Evolution of shapes in 59Cu

High-spin states in ⁵⁹Cu were populated using the fusion-evaporation reaction ²⁸Si + ⁴⁰Ca at a beam energy of 122 MeV. The Gammasphere Ge-detector array in conjunction with the 4π charged-particle detector array Microball allowed for the detection of γ-rays in coincidence with evaporated light particles. The resulting extensive high-spin decay scheme of ⁵⁹Cu is presented, which comprises more than 320 γ-ray transitions connecting about 150 excited states. Their spins and parities have been assigned via directional correlations of γ-rays emitted from oriented states. Average quadrupole moments of rotational bands have been determined from the analysis of residual Doppler shifts. Shell model calculations in the fp shell are invoked to study some of the low-spin states, while the experimental characteristics of the rotational bands are analyzed in the configuration-dependent cranked Nilsson-Strutinsky (CNS) approach. Received: 15 February 2002 / Accepted: 23 April 2002     

Observation of signature inversion in odd-odd 178Ir

High spin states in ¹⁷⁸Ir have been studied via the ¹⁵²Sm(³¹P, 5nγ)¹⁷⁸Ir reaction through excitation functions, X-γ and γ-γ-t coincidence measurements. According to the band structure characteristics and the measured intraband B(M1)/B(E2) ratios, two rotational bands are identified and assigned to be associated with the πh _9/2⊗νi _13/2 and πh _11/2⊗νi _13/2 configurations, respectively. Both bands show the signature inversion feature. Received: 23 March 2000 / Accepted: 31 July 2000     

Lifetime study of high-spin states in 104,105In

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. Received: 30 June 1998     

High-spin states following multi-nucleon transfer

High-spin states in neutron-rich nuclei, populated following deep-inelastic multi-nucleon transfer, have been studied using the GAMMASPHERE array at the LBNL, USA. A ⁶⁴Ni beam at an energy ∼ 15% above the Coulomb barrier was incident upon a thick ²⁰⁸Pb target, leading to the population of more than 130 different nuclei. The strongest channels correspond to nuclei close to the projectile and target, although transfer of up to 50 nucleons has been observed. New high-spin states in neutron-rich ^60,62Fe and ^68,70,72Zn nuclei have been observed. Some limitations of this method of high-spin spectroscopy are discussed, including the apparent difficulty of populating odd-odd and odd-even isotopes via this type of reaction. The data have been searched for superdeformed (SD) states in the A = 190-200 region, but no evidence for their presence has been found. Received: 14 April 2000 / Accepted: 12 September 2000     

Identification of band structures in the 137La nucleus

High-spin states of ¹³⁷La have been investigated with the reaction ¹³⁰Te(¹¹B, 4n) at a beam energy of 50MeV. The level scheme of ¹³⁷La has been expanded with spin up to 33/2ℏ. Several new bands have been found in this nucleus. A band crossing in the band based on the 17/2^- level has been observed at a rotational frequency of ℏω ∼ 0.48MeV. From systematic comparison, this band crossing probably originates from the alignment of protons. One of the bands with strong M1 transitions is proposed as a collective oblate band ( γ ∼ -60^°).     

High-spin states in 44Ca

High-spin states of the ⁴⁴Ca nucleus populated in the 68 MeV ¹⁸O + ³⁰Si reaction have been studied in a γ-γ-recoil coincidence experiment. The level scheme of ⁴⁴Ca has been extended up to 12.2 MeV. In particular, the negative-parity band has been identified with the highest I = 13^- level at 10.6 MeV. This state is interpreted as the band-terminating state for the ( d _3/2 ^-1 f _7/2 ⁵) configuration. Received: 7 November 2001 / Accepted: 3 December 2001     

Precise determination of the neutron scattering length of lead isotopes <Superscript>204</Superscript>Pb, <Superscript>207</Superscript>Pb and <Superscript>208</Superscript>Pb by neutron interferometry

Excited states of ⁶⁸Ga have been investigated through the ⁵⁵Mn(¹⁶O, 2pn) reaction at projectile energy 55 MeV. The level scheme has been extended up to 7.8 MeV. Altogether six new excited levels could be identified and twelve previously unobserved γ-transitions have been placed in the modified level scheme. Received: 19 June 2000 / Accepted: 20 October 2000     

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 states and evidence for octupole correlations in 117Xe

High-spin states of ¹¹⁷Xe were investigated by means of in-beam γ-ray spectroscopic techniques via the reaction of ²⁸Si bombarding a ⁹²Mo target at beam energies of 100-120 MeV. A positive-parity rotational band decaying into the yrast negative-parity band by a series of enhanced E1 transitions was observed for the first time, implying the existence of octupole correlations in ¹¹⁷Xe. The B(E1) values increase with spin. The νd_5/2 band was firmly established up to 27/2⁺ and the B(M1)/B(E2) ratios were extracted from the relative intensities of γ-rays in this band. The previously known νh_11/2 and νg_7/2 [413]5/2⁺α=−1/2 bands were confirmed and extended up to high spins and two bandcrossings are observed in the latter at ħω=0.33 and 0.44 MeV, respectively. The bandcrossings and configurations of these bands are discussed by TRS and CSM calculations. In a γ–γ–t measurement, the 11/2⁻ and 7/2⁻ levels were identified as two isomers with half-lives of 59.4±20 ns and 16.5±8.0 ns, respectively. Received: 17 June 1997 / Revised version: 29 September 1997