Investigation of lifetimes in dipole bands of 142Gd

Lifetimes have been measured for dipole bands in ¹⁴²Gd using DSAM. The deduced B(M1) and B(E2) values as well as B(M1)/B(E2) ratios are compared with calculations in the framework of the TAC (Tilted Axis Cranking) and SPAC (Shears mechanism with Principal Axis Cranking) models. The dipole bands DB1 to DB4 can be interpreted as magnetic rotational bands.     

Investigation of lifetimes in the dipole band of 139Sm

Lifetimes have been measured for a dipole band in ¹³⁹Sm using DSAM. The deduced B(M1) and B(E2) values as well as B(M1)/B(E2) ratios are compared with calculations in the framework of the TAC (Tilted Axis Cranking) and SPAC (Shears mechanism with Principal Axis Cranking) models. The dipole band in ¹³⁹Sm can be considered as a magnetic rotational band with a prolate or triaxial nuclear deformation.     

Configuration assignments of yrare high-spin structures in 126Cs

High-spin states in ¹²⁶Cs were populated in the reaction ¹¹⁶Cd(¹⁴N, 4n) at a beam energy of 65 MeV. About 50 new transitions were placed in a level scheme that consists of six rotational structures, three of which have been observed for the first time. The newly observed bands and a previously reported but uninterpreted band were assigned configurations based on their population, aligned angular momentum, energy signature splitting and B(M1)/B(E2) ratios (for the strongly coupled bands).Received: 16 September 2002, Revised: 10 March 2003, Published online: 1 July 2003PACS: 21.10.Re Collective levels - 27.60.+j      

Investigations of the level scheme of 144Gd and lifetimes in the quadrupole bands

For a level scheme investigation of ¹⁴⁴Gd an experiment with the -spectrometer EUROBALL III has been carried out and lifetimes have been measured with the -spectrometer GASP using the Doppler-shift attenuation method. The high-spin states have been populated in these experiments by means of the ¹⁰⁰Mo(⁴⁸Ti,4n) reaction at 215 MeV and the ¹¹⁴Cd(³⁶S,6n) reaction at E = 182 MeV, respectively. The known quadrupole band has been modified and a new one has been established. Reduced E2 transition probabilities B(E2) were determined for seven members of these quadrupole bands. They show values between and 130 W.u. and this considerable enhancement gives evidence for a significant nuclear deformation. A configuration may be assigned to one of the quadrupole bands according to total Routhian surface calculations. The spin dependence of the B(E2) values has been explained by IBM calculations involving high-spin quasiparticle excitations.Received: 5 June 2003, Revised: 10 December 2003, Published online: 23 July 2004PACS: 21.10.Re Collective levels - 21.10.Tg Lifetimes - 21.60.Fw Models based on group theory - 27.60. + j      

A new isomer in 136 Ba populated by deep inelastic collisions

Excited states in ¹³⁶Ba, populated in deep inelastic collisions by the interaction of 450 MeV ⁸²Se ions with a ¹³⁹La target, have been studied by means of in-beam -ray spectroscopy. A new isomer with has been identified at an excitation energy E_x = 3.357 MeV. The half-life was determined as ns. The extracted B(E2) value is much smaller than those in ¹³²Te and ¹³⁴Xe. This hindrance is investigated by a shell model calculation.Received: 22 September 2003, Revised: 11 November 2003, Published online: 6 April 2004PACS: 21.10.Tg Lifetimes - 23.20.Lv transitions and level energies - 27.60. + j      

Study of <Emphasis Type="Italic">N</Emphasis> = <Emphasis Type="Italic">Z</Emphasis> nuclei in variation-after-projection framework

Variation-after-projection (VAP) calculations in conjunction with the Hartree- Bogoliubov (HB) ansatz have been carried out for A = 68-88, N = Z nuclei. In this framework, the yrast spectra with , B(E2) transition probabilities and deformation parameter ( ) have been obtained. A pairing interaction for like particles as well as protons and neutrons has been included in the model for a two-body interaction.Received: 28 April 2003, Revised: 20 March 2004, Published online: 14 September 2004PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 21.60.-n Nuclear structure models and methods - 27.50. + e      

Collectivity and single-particle degrees of freedom

Intruder rotational bands in ⁴⁵Sc and ⁴⁵Ti have been investigated up to the maximum aligned angular momentum by means of EUROBALL IV and the Recoil Filter Detector (RFD). The use of the RFD allowed for a reduction of the -line Doppler broadening and, moreover, for a determination of very short level lifetimes. In the studied nuclei, the estimated deformation shows a gradual disappearance of the collectivity at the highest available spins.Received: 19 November 2002, Revised: 14 March 2003, Published online: 2 March 2004PACS: 21.10.Tg Lifetimes - 21.60.Cs Shell model - 27.40. + z P. Bednarczyk: Present address: GSI, Darmstadt, GermanyM.B. Smith: Present address: TRIUMF, Vancouver, Canada     

Study of thermally excited nuclei through <Emphasis Type="Italic">E</Emphasis>1 and <Emphasis Type="Italic">E</Emphasis>2 decay from collective modes

The nuclear system at the limit of excitation energy and angular momentum is here studied in the case of the superdeformed nucleus ¹⁴³Eu using -spectroscopy techniques. The data are based on a EUROBALL experiment using the reaction ³⁷Cl + ¹¹⁰Pd Eu + 4n. The influence of thermal energy on superdeformed configurations is investigated through the analysis of the quasi-continuum spectra formed by E2 transitions among states of excited rotational bands with energy extending up to 4-5 MeV above the yrast line. In particular, the effective lifetimes of the discrete rotational bands forming ridge structures in - coincidence matrices is measured by a Doppler Shift Attenuation Method. The deduced quadrupole deformation of 10 eb indicates that the nucleus maintains its collectivity with increasing excitation energy, supporting the superdeformed character of the excited nuclear rotation. The obtained number of superdeformed discrete bands forming the ridge structures is found in good agreement with microscopic cranked shell model calculations including the decay-out process into the lower deformation minimum. In addition, the nuclear properties at higher excitation energies are investigated through the E1 -decay of the giant dipole resonance (GDR). It is found that the intensity of the superdeformed yrast and excited bands increases by a factor of approximately 1.6 when a coincidence with a high-energy -ray is required, showing the importance of the E1 cooling in the feeding mechanism of the superdeformed states.Received: 2 December 2002, Published online: 2 March 2004PACS: 21.10.Tg Lifetimes - 21.10.Re Collective levels - 23.20.Lv transitions and level energies - 27.60. + j      

Shell model calculations with modified empirical Hamiltonian in the <Superscript>132</Superscript>Sn region

Using recent experimental information for the ¹³²Sn region, an empirical Hamiltonian is obtained by some modifications of a Hamiltonian (CW5082) originally derived from the ²⁰⁸Pb region. Shell model calculations with the new Hamiltonian show a remarkable improvement in the predictive power when compared with the available experimental results. It overcomes many limitations of the CW5082 Hamiltonian in this region, specially for isotones. The calculated level spectra and B(E2) values with the new Hamiltonian, also compare well with the available results calculated with the CD-Bonn and SKX Hamiltonians, reflecting consistency in the wave function structure at least in the low-lying regions. An interesting behaviour of effective charges is revealed in this region. It is shown that a drastic reduction of proton effective charge is necessary for obtaining B(E2) values for the N = 84 isotones. Neutron effective charge is found to be in the range (0.62-0.72)e. We predict the spectroscopic properties of ^135,136Sn not yet known experimentally. Further improvement of the modified Hamiltonian is also initiated.Received: 25 September 2003, Revised: 20 January 2004, Published online: 13 July 2004PACS: 21.60.Cs Shell model - 21.10.-k Properties of nuclei, nuclear energy levels - 23.20.-g Electromagnetic transitions - 27.60. + j      

Multiple Coulomb excitation experiment of 66 Zn

A Coulomb excitation experiment was carried out with a ⁶⁶Zn beam bombarding a Pb target. Four E2 matrix elements and the quadrupole moment of the 2₁ ⁺ state were derived with the least-squares search code GOSIA. According to the B(E2) values, the ground band can be interpreted as a quasirotational band. It was found that the 2₁ ⁺ level has a positive quadrupole moment, which may be interpreted as a soft triaxial deformation.Received: 28 January 2003, Revised: 18 March 2003, Published online: 9 October 2003PACS: 25.70.De Coulomb excitation - 21.10.Ky Electromagnetic moments - 23.20.-g Electromagnetic transitions - 27.50.+e      

Systematics of deformed states around doubly-magic <Superscript>40</Superscript>Ca

The low-lying rotational bands of A = 36-48 nuclei are consistently explained by starting from the recently discovered, superdeformed intrinsic state of ³⁶Ar as the core, filling successively the first three Nilsson orbits above the Fermi border. The critical single-particle energies were obtained from experimental data as were the residual interactions in the parametrization of Brink and Kerman. Implicit are the rearrangement energies due to configuration-dependent equilibrium deformations. The binding energies of 20 experimental bandheads were used to derive the parameters while another 38 bandheads were subsequently predicted and identified almost completely. The Racavy expression reduced by 20% reproduces or predicts the values of the deformation parameter . The empirical Nilsson model amended by -vibrational and rotation-aligned bands accounts completely for the multi-particle excitations from the N = 2 into the N = 3 major shell which are not accessible by shell-model calculations. In the case of ⁴⁰Ca a spectrum of 42 states below E _x = 8 MeV is explained.PACS: 21.60.Ev Collective models - 21.10.Dr Binding energies and masses - 27.30. + t - 27.40. + z      

Viewing the proton through “color” filters

A seven-quasiparticle isomer with and T _1/2 = 53 ( ^{+ 3} _-7) ns has been identified in ¹⁷⁹Ta. By comparing its excitation energy with results from multi-quasiparticle calculations that include the effects of blocking and residual nucleon-nucleon interactions, the isomer is assigned the (5/2 ⁺ [402], 7/2 ⁺ [404], (5/2^-[512], 7/2^-[514], 7/2^-[503], 9/2 ⁺ [624]) configuration. The decay of this isomer is found to be unusually fast, a feature that is attributed to a mixing with a specific collective level. The interaction strength is found to be orders of magnitude lower than that observed between interacting collective levels.Received: 7 March 2004, Revised: 3 May 2004, Published online: 5 October 2004PACS: 21.10.Re Collective levels - 21.10.Tg Lifetimes - 23.20.Lv Gamma transitions and level energies - 27.70. + q S.J. Freeman: Present address: Department of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.G . Mukherjee: Present address: Nuclear and Atomic Physics Division, Saha Institute of Nuclear Physics, Kolkata 700 064, India.     

Complete spectroscopy in high-spin cranking calculations

Exact and approximate quantum numbers of the cranked Nilsson-Strutinsky (CNS) formalism are exploited to calculate excited bands in fixed configurations with the energy of the individual bands minimized with respect to deformation for all spin values. The formalism is applied to ⁵⁹Cu, where all bands which appear important in the decay out of the superdeformed band are calculated.Received: 14 November 2002, Published online: 17 February 2004PACS: 21.10.Ma Level density - 21.60.Cs Shell model - 23.20.Lv transitions and level energies - 27.50. + e C. Andreoiu: Present address: Department of Physics, University of Guelph, Guelph, Ontario, Canada N1G 2W1.     

Multi-quasiparticle states in 184 W via multi-nucleon transfer

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 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.Received: 14 October 2003, Revised: 14 November 2003, Published online: 18 May 2004PACS: 21.10.Tg Lifetimes - 23.20.Lv transitions and level energies - 27.70. + q      

Hard-to-reach nuclei studied with deep-inelastic heavy-ion reactions

Spectroscopic studies performed with deep-inelastic heavy-ion reactions are reviewed for two regions of neutron-rich nuclei. The identification of isomers in nearly complete series of Sn isotopes and the resulting systematic of B(E2) values for isomeric transitions is presented and followed by the discussion of shell model states studied in neutron-rich Te isotopes including the new four neutron-hole isomers identified in ¹³⁰Te. Yrast spectroscopy studies of nuclei from the doubly magic ²⁰⁸Pb region are described by outlining the highest spin states observed in the ²⁰⁸Pb core nucleus. The E3 transitions observed abundantly in yrast decays are discussed within the framework of particle-octupole vibration coupling and the validity of a simple rule connecting energy shifts of octupole states built on one-particle states with the ones observed for two-particle states is demonstrated.Received: 15 January 2003, Published online: 23 March 2004PACS: 21.60.Cs Shell model - 23.20.Lv transitions and level energies - 27.60. + j - 27.80. + w      

Reinvestigation of the beta-decay of 110Mo

The beta-decay of the neutron-rich nucleus ¹¹⁰Mo, separated by the IGISOL on-line mass separator from other fission products, has been investigated by using beta-gamma and gamma-gamma coincidence techniques. The decay scheme of ¹¹⁰Mo has been revised, including 3 new excited states and 7 new transitions in ¹¹⁰Tc. The -feedings were measured and values and B(GT) values were deduced based on a -value from systematics. Three excited 1 ⁺ states in ¹¹⁰Tc fed by spin-flip allowed-unhindered beta transitions were identified. The deduced beta-decay strengths are compared with the Gamow-Teller strength distribution obtained from a macroscopic-microscopic calculation. The role of the asymptotic quantum numbers in the context of the allowed beta-decay is discussed.Received: 5 May 2003, Revised: 13 June 2003, Published online: 26 November 2003PACS: 27.60. + j - 21.10.Tg Lifetimes - 23.20.Lv Gamma transitions and level energiesJ.C. Wang: Present address: Argonne National Laboratory, 9700 S. Cass Ave., Room F-133, Bldg 203, Argonne, IL 60439, USA;     

Wobbling phonon excitations in strongly deformed triaxial nuclei

The wobbling mode is uniquely related to triaxiality and introduces a series of bands with increasing wobbling phonon number, . The pattern of -transitions between the wobbling excitations will be influenced by the presence of an aligned particle. Evidence for the wobbling mode was obtained recently, and even a two-phonon wobbling excitation has now been identified in ¹⁶³Lu. The similarity of the data in ¹⁶³Lu to new strongly deformed triaxial bands and connecting transitions in the neighbouring nuclei, ¹⁶⁵Lu and ¹⁶⁷Lu, establishes wobbling as a more general phenomenon in this region. The higher phonon wobbling excitations show some anharmonicity, but the characteristic large E2 strength is observed. The wobbling interpretation is based on the comparison of electromagnetic decay strength between bands to particle-rotor calculations in which an i_13/2 proton is coupled to a triaxial core.Received: 30 October 2002, Published online: 23 March 2004PACS: 27.70. + q - 23.20.-g Electromagnetic transitions - 21.10.Re Collective levels     

Excited states in 163,164Ho populated through incomplete-fusion reactions

High-spin states in ^163,164Ho were investigated by means of in-beam -ray spectroscopy techniques using the multidetector array GASP. Excited states in ^163,164Ho were populated predominantly through the incomplete-fusion mechanism in the ¹⁶⁰Gd (¹¹B reaction at a beam energy of 61 MeV. Known rotational bands in ¹⁶³ Ho have been extended to higher spins and a three-quasiparticle band has been observed in this nucleus. Rotational bands have been identified in ¹⁶⁴Ho and their configurations have been discussed. Empirical Gallagher-Moszkowski (GM) splitting energies were extracted from the and GM doublets. Alignments, band crossing frequencies, and electromagnetic properties have been analyzed in the framework of the cranking model.Received: 13 February 2004, Revised: 18 March 2004, Published online: 14 September 2004PACS: 21.10.Re Collective levels - 21.60.Ev Collective models - 23.20.Lv transitions and level energies - 27.70. + q