Relativistic Hartree-Bogoliubov description of deformed light nuclei

The Relativistic Hartree-Bogoliubov model is applied in the analysis of ground-state properties of Be, B, C, N, F, Ne and Na isotopes. The model uses the NL3 effective interaction in the mean-field Lagrangian, and describes pairing correlations by the pairing part of the finite-range Gogny interaction D1S. Neutron separation energies, quadrupole deformations, nuclear matter radii, and differences in radii of proton and neutron distributions are compared with recent experimental data.Received: 27 August 2003, Revised: 12 March 2004, Published online: 19 October 2004PACS:   21.60.Jz Hartree-Fock and random-phase approximations - 21.10.Gv Mass and neutron distributions - 27.20. + n - 27.30. + t      

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      

Study of the double-beta-decay of 100 <A$ \leq 150$ nuclei within the QRPA,RQRPA and the SRQRPA formalisms

We have used a self-consistent version of the BCS + RQRPA method for a systematic study of the two-neutrino double-beta-decay of nuclei with . The comparison with other approaches, namely the QRPA and the RQRPA, shows that inclusion of the quasiparticle correlations at the BCS level reduces the ground-state correlations in the particle-particle channel of the proton-neutron interaction. This in turn results in a systematic reduction of the double-beta-decay matrix elements. The effect of the extension of the formalism on the Ikeda sum rule has been discussed.Received: 28 July 2003, Published online: 5 February 2004PACS: 21.60.Jz Hartree-Fock and random-phase approximations - 23.40.Bw Weak-interaction and lepton (including neutrino) aspects - 23.40.Hc Relation with nuclear matrix elements and nuclear structure - 27.60. + j      

\alpha-decay spectroscopy of light odd-odd Bi isotopes - I: 188,190Bi nuclei

Detailed fine-structure -decay studies of ^188,190Bi were performed using the complete-fusion reactions of ^50,52Cr ions with a ¹⁴²Nd target at the velocity filter SHIP. The evaporation residues were separated in-flight and subsequently identified on the basis of recoil- , recoil- - /X-ray and excitation function measurements. Improved data on the -decay of ^188,190Bi were obtained and a number of new low-lying excited states in the daughters ^184,186Tl were observed. An intruder, presumably 10^- state was identified in ¹⁸⁴Tl, extending the systematics of such states in the odd-odd Tl nuclei beyond the neutron mid-shell at N = 104. Some technical aspects of experiment at recoil separators are also discussed.Received: 14 March 2003, Revised: 1 May 2003, Published online: 2 September 2003PACS: 23.60.+e decay - 27.70.+q - 27.80.+w C.D. OLeary: Present address: Department of Physics, University of York, York, UK.M.J. Taylor: Present address: Department of Physics and Astronomy, Rutgers Univesity, NJ, USA.L. Weissman: Present address: NSCL, Michigan State University, East Lansing, MI 48824-1321 USA.K. Heyde: Present address: EP-ISOLDE, CERN, CH-1211, Geneva 23, Switzerland.     

Two-quasiparticle and collective excitations in transitional 108,110 Pd nuclei

High-spin states in ^108,110Pd isotopes are studied by -ray spectroscopy of heavy-ion-induced fission. The Pd isotopes are produced in the fission channel of the ³¹P + ¹⁷⁶Yb reaction at beam energy 152 MeV. The prompt -rays are detected with the EUROBALL4 multidetector array. The yrast states of ^108,110Pd have been observed above the region of the first backbend. The level scheme of ¹⁰⁸Pd was extended with a new negative-parity band. The yrast sequence in ¹¹⁰Pd is observed up to spin I = 14 ⁺ and negative-parity bands have also been identified. The backbending in these even-mass Pd isotopes is associated with the alignment of the neutron (h _11/2)² pair. The negative-parity states arise from two neutron configurations and and they are interpreted in the frame of two-quasiparticle + rotor model as semidecoupled bands. The observed experimental staggering in the -bands of ^108,110Pd supports the theoretical predictions for -instability of their shapes.Received: 22 April 2003, Revised: 27 June 2003, Published online: 2 December 2003PACS: 21.60.-n Nuclear structure models and methods - 23.20.Lv transitions and level energies - 25.70.Jj Fusion and fusion-fission reactions - 27.60. + j      

Level structure of 146Tb

The level structure of the doubly odd nucleus ¹⁴⁶Tb has been studied via the ¹¹⁸Sn(³²S, 1p3n) reaction using techniques of in-beam -ray spectroscopy. Measurements of -ray anisotropies, X- and - -t coincidences were performed with 12 BGO(AC)HPGe detectors. Based on the measured results, the level scheme of ¹⁴⁶Tb has been revised significantly and extended up to an excitation energy of 8.39 MeV. The level structure has been interpreted qualitatively by coupling an h _11/2 proton-particle and an h _11/2 neutron-hole to the excited states in the ¹⁴⁶Gd core.Received: 3 July 2003, Published online: 26 November 2003PACS: 23.20.Lv transitions and level energies - 27.60. + j      

Boltzmann-Uehling-Uhlenbech calculation of total reaction cross-section and fragmentation cross-section

, and have been calculated via the BUU model with soft EOS and 0.8 times of . The density distribution without any adjustable parameters which comes from the RMF model has been introduced into the BUU calculation to replace the normally used one-parameter square-type distribution. The calculated results can reproduce the experimental data well for both halo- and stable-nuclei-induced reactions. Here or is calculated as the difference between of halo nucleus and core nucleus, by assuming . It indicates that this assumption works very well at high energy in the BUU calculation. More experimental measurements are necessary to test the validity of this assumption at intermediate energy.Received: 12 June 2003, Revised: 29 September 2003, Published online: 27 April 2004PACS: 24.10.-i Nuclear reaction models and methods - 25.60.Dz Interaction and reaction cross-sections - 25.60.Gc Breakup and momentum distributions - 27.20. + n      

Energy dependence of the Λ/Σproduction cross-section ratio in p-p interactions

The production of the - and -hyperons has been measured via the reaction at the internal COSY-11 facility in the excess energy range between 14 and 60 MeV. The transition of the cross-section ratio from about 28 at MeV to the high-energy level of about 2.5 is covered by the data showing a strong decrease of the ratio between 10 and 20 MeV excess energy. Effects from the final-state interactions in the p- channel seem to be much smaller than in the p- channel. Estimates of the effective range parameters are given for the and the systems.PACS: 13.75.-n Hadron-induced low- and intermediate-energy reactions and scattering (energy GeV) - 13.75.Ev Hyperon-nucleon interactions - 13.85.Lg Total cross-sections - 25.40.Ep Inelastic proton scattering     

Isomeric and ground-state decay of 215 Bi

A new high-spin isomer in ²¹⁵Bi, with a half-life of 36.9(6) s, has been identified at the PSB-ISOLDE on-line mass separator using the pulsed-release technique combined with the element selective RILIS source. A decay scheme of Bi was constructed and complemented with the low-spinstructure observed in Bi decay. The population of a cascade on top of the level in ²¹⁵Poprovides evidence for Gamow-Teller -decay of the high-spin ²¹⁵Bi isomer.Received: 3 March 2003, Revised: 10 June 2003, Published online: 9 October 2003PACS: 23.20.Lv transitions and level energies - 27.80.+w - 29.30.Kv X- and -ray spectroscopyV. Fedoseyev: Present address: ISOLDE, CERN-PPE, CH-1211, Geneva 23, Switzerland.M. Górska: Present address: GSI, Darmstadt, D-64220, Germany.M. Huhta: Present address: Nokia, Tampere, Finland.     

First structure information on the exotic 149 La from the $\beta^-$-decay of 149 Ba

The -decay of ¹⁴⁹Ba to ¹⁴⁹La has been investigated by means of - and X-ray spectroscopy, and a partial level scheme of ¹⁴⁹La has been constructed for the first time. It includes thirteen -rays and ten excited states. The exotic ¹⁴⁹La is the heaviest lanthanum for which spectroscopic information is now available. We have applied the shell correction approach with the axially deformed Woods-Saxon potential in order to calculate the deformation energy for the ¹⁴⁹La ground state. The deformed ground state was found at 0.23, 0 and 0.12.Received: 18 July 2003, Revised: 12 January 2004, Published online: 26 May 2004PACS: 27.60. + j - 29.30.Kv X- and -ray spectroscopy     

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      

Extended RPA with ground-state correlations

We propose a time-independent method for finding a correlated ground state of an extended time-dependent Hartree-Fock theory, known as the time-dependent density matrix theory (TDDM). The correlated ground state is used to formulate the small amplitude limit of TDDM (STDDM) which is a version of extended RPA theories with ground-state correlations. To demonstrate the feasibility of the method, we calculate the ground state of ²² O and study the first 2 ⁺ state and its two-phonon states using STDDM.Received: 7 November 2003, Published online: 10 August 2004PACS: 21.10.Re Collective levels - 21.60.Jz Hartree-Fock and random-phase approximations - 27.30. + t      

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      

First identification of excited states in the T_z\! = \!1/2 nucleus 93 Pd

The first experimental information about excited states in the N = Z + 1 nucleus ⁹³Pd is presented. The experiment was performed using a 205 MeV ⁵⁸Ni beam from the Vivitron accelerator at IReS, Strasbourg, impinging on a bismuth-backed ⁴⁰Ca target. Gamma-rays, neutrons and charged particles emitted in the reactions were detected using the Ge detector array Euroball, the Neutron Wall liquid-scintillator array and the Euclides Si charged-particle detector system. The experimental level scheme is compared with the results of new shell model calculations which predict a coupling scheme with aligned neutron-proton pairs to greatly influence the level structure of nuclei at low excitation energies.Received: 28 October 2003, Revised: 4 December 2003, Published online: 26 January 2004PACS: 21.10.Hw Spin, parity, and isobaric spin - 23.20.Lv transitions and level energies - 27.60. + j - 21.60.Cs Shell model     

Pseudo-spin band in the odd-odd nucleus 172Lu

High-spin states in the odd-odd nucleus ¹⁷²Lu have been populated in a ¹⁷⁰Er(⁷Li, 5n) reaction and the emitted -radiation was detected with the GASP array. Two sequences of a new identical band have been observed with the transition energies in the favoured and unfavoured sequences being identical within keV at low spins and keV at high spins over the whole observed spin range. Aninterpretation as a pseudo-spin singlet band of configuration is proposed. It represents the best example of a pseudo-spin singlet band in normal deformed nuclei known until now.Received: 19 February 2003, Revised: 27 March 2003, Published online: 12 August 2003PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 21.10.Re Collective levels - 23.20.Lv transitions and level energies - 27.70.+q      

The influence of the entrance channel dynamics on the evaporation residue formation

The dynamical effects of the entrance channel on the competition between quasifission and fusion processes, and on the evaporation residue formation are investigated. We have analyzed the results and compared our calculations with the experimental data obtained in the ¹⁶ O + ²⁰⁴ Pb and ⁹⁶ Zr + ¹²⁴ Sn reactions having very different mass asymmetries and leading to the ²²⁰ Th ^* compound nucleus. We have found that different partial capture cross-sections for these reactions lead to different fusion-quasifission competitions and, consequently, to different partial fusion cross-sections of the compound nucleus formed in the two reactions. The dynamical conditions also affect the fission-evaporation competition of the excited intermediate nuclei along the CN de-excitation cascade and, consequently, the evaporation residue formation.Received: 8 March 2004, Revised: 5 April 2004, Published online: 25 October 2004PACS: 25.70.Jj Fusion and fusion-fission reactions - 25.70.-z Low and intermediate energy heavy-ion reactions - 27.80. + w - 27.90. + b      

Study of drip line nuclei through two-step fragmentation

We have studied the structure of light neutron-rich nuclei around N = 16 by employing the in-beam -ray spectroscopy technique using the fragmentation of secondary beams of ^25,26Ne, ^27,28Na and ^29,30Mg isotopes. This secondary-beam cocktail was obtained by the fragmentation of a ³⁶S beam at 77.5 MeV by the SISSI/GANIL facility. By a second-step fragmentation, we have measured -ray-residue coincidences in ^17-20C and ^23,24O and described the obtained levels in the framework of the shell model.Received: 31 October 2002, Published online: 24 February 2004PACS: 23.20.Lv transitions and level energies - 21.60.Cs Shell model - 27.20. + n - 27.30. + t