Single-particle quadrupole electromagnetic transitions in p-shell and sd-shell nuclei

Electron scattering Coulomb form factors for the single-particle quadrupole transitions in p-shell and sd-shell nuclei have been studied. Core polarization effects are included through a microscopic theory that includes excitations from the core orbits up to higher orbits with 2ω excitations. The modified surface delta interaction is adopted as a residual interaction. The results are discussed for the ( 1p _1/2 ^-1↦1p _3/2 ^-1) proton transition in ¹⁵N, ( 1d _5/2↦2s _1/2) neutron transition in ¹⁷O and ( 1d _3/2 ^-1↦2s _1/2 ^-1) proton transition in ³⁹K. The inclusion of core polarization effects modifies the form factors markedly and describes the experimental data very well in both the absolute strength and the momentum transfer dependence. Received: 18 April 2002 / Accepted: 1 July 2002 / Published online: 6 March 2003 RID="a" ID="a"e-mail: baguniv@uruklink.net Communicated by A. Molinari     

Perturbative role in the inelastic electron scattering from <Superscript>29</Superscript>Si

Inelastic electron scattering form factors away from the closed sd -shell are investigated. This investigation covers the low-lying states in ²⁹Si , which is considered according to the many-particle configuration mixing shell model as the ¹⁶O core, plus thirteen nucleons distributed over the entire sd -shell orbits. The investigation concentrates on the perturbative role of the core, which is called core polarization effects, on the inelastic electron scattering form factors. Core polarization effects are taken into consideration through the excitation of nucleons from 1s and 1p core orbits, and also from the 2s -1d valence orbits into higher shells, with 2ℏω excitations. Core polarization matrix elements are calculated with the M3Y effective interaction. For the sd -shell model space, a new Hamiltonian, based on a renormalized G -matrix, USDB, is used. All calculations are performed without adjusting any parameters.     

Rotational alignment of the h11/2 band in 157Dy

High-spin states of ¹⁵⁷Dy were investigated using in-beam γ-ray spectroscopy techniques with a ¹⁵⁰Nd(¹²C, 5n) reaction. Three rotational bands with the h _9/2, i _13/2 and h _11/2 configurations were observed up to (43/2^-), 53/2⁺ and 45/2^-, respectively. Interband M1 transitions in the h _11/2 (high-Ω) band were also measured up to the highest-spin state. The high-spin states were well reproduced by calculations using the tilted-axis-cranking model (TAC). The B(M1)/B(E2) ratio, Routhian and the tilted angle of the angular-momentum vector are found to be in good agreement with the result of the TAC calculation. Received: 22 August 2002 / Accepted: 26 September 2002 / Published online: 19 November 2002 RID="a" ID="a"e-mail: hayakawa@jball4.tokai.jaeri.go.jp Communicated by W. Henning     

In-beam γ-ray spectroscopy of 42Ca

High-spin states of the ⁴²Ca nucleus, populated in the 68 MeV ¹⁸O + ³⁰Si reaction, have been studied in a γ-γ-recoil coincidence experiment. The level scheme of ⁴²Ca has been extended up to 13.7 MeV. An elaborate decay pattern with various paths, together with high-quality DCO and polarization information assigns spins and parities for almost all observed levels. The sequence of non-yrast positive-parity states is discussed and compared with highly deformed bands in ³⁶Ar and ⁴⁰Ca. Received: 26 November 2002 / Accepted: 11 December 2002 / Published online: 18 February 2003 RID="a" ID="a"e-mail: Malgorzata.Lach@ifj.edu.pl RID="b" ID="b"Present address: TRIUMF, Vancouver, Canada. RID="†" ID="†"Deceased. Communicated by D. Schwalm     

Decoupling and coherence in E1 and E2 moments in drip line nuclei

I discuss first the effect of decoupling of extended wave functions and the coherence in the low-energy E1 strength in drip line nuclei ¹²Be and ¹³O, which are studied by large-scale shell model calculations including 3 ?ω configuration space. The calculated results are compared to recent experimental data of Coulomb excitations. The quenching of the core polarization charges in drip line nuclei is also discussed in relation to recent observations of quadrupole moments in B-isotopes. Received: 1 May 2001 / Accepted: 4 December 2001     

High-spin study of odd- A 49In isotopes beyond the neutron mid-shell

The ^{115, 117, 119, 121}In nuclei have been produced as fission fragments in three reactions induced by heavy ions: ¹²C + ²³⁸U at 90MeV bombarding energy, ¹⁸O + ²⁰⁸Pb reaction at 85MeV, and ³¹P + ¹⁷⁶Yb at 152MeV. Their level schemes have been built from gamma-rays detected using the EUROBALL III and IV arrays. High-spin states of ^{117, 119, 121}In nuclei have been identified for the first time. Moreover, isomeric states lying around 2.5MeV have been established in ^{119, 121}In from the delayed coincidences between the fission fragment detector SAPhIR and the gamma array. Most of the observed states can be described by coupling a proton g _9/2 hole to a Sn core, while the intruder band based on an orbital from the π[g _7/2/d _5/2] sub-shells behaves as the ground-state band of neighbouring Cd isotopes. Received: 24 May 2002 / Accepted: 11 June 2002 / Published online: 19 November 2002 RID="a" ID="a"e-mail: porquet@csnsm.in2p3.fr RID="b" ID="b"Present address: CEA-DIF, DAM/DCRE/SDE/LDN, 91680 Bruyères-le-Chatel, France. RID="c" ID="c"Present address: CSNSM IN2P3-CNRS and Université Paris-Sud 91405 Orsay, France. RID="d" ID="d"Present address: CEA/Saclay, DSM/DAPNIA/SPhN, 91191 Gif-sur-Yvette Cedex, France. Communicated by D. Schwalm     

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     

High-spin structure of the neutron-rich odd-odd 106, 108 45Rh and 110, 112 47Ag isotopes

The ^{106, 108}Rh and ^{110, 112}Ag nuclei have been produced as fission fragments following the fusion reaction ²⁸Si + ¹⁷⁶Yb at 145 MeV bombarding energy and studied with the Eurogam2 array. The yrast high-spin states of these four odd-odd nuclei, which are observed for the first time, consist of rotational bands in which the odd proton occupies the πg _9/2 subshell and the odd neutron the νh _11/2 subshell. Their behaviour as a function of spin values does not vary with the number of neutrons: as observed in the odd-N neighbouring nuclei, the motion of the odd neutron remains decoupled from the motion of the core, from N = 61 to N = 65. Moreover, the staggering observed in the yrast bands of odd-odd isotopes is strongly reduced as compared to the large values displayed by the rotational bands built on the πg _9/2 subshell in the odd-A Rh and Ag isotopes. The results of particle-rotor calculations indicate that this reduction is related to a change of the core deformation. Received: 1 June 2001 / Accepted: 23 July 2002 / Published online: 10 December 2002 RID="a" ID="a"e-mail: porquet@csnsm.in2p3.fr RID="b" ID="b"Present address: CSNSM IN2P3-CNRS and Université Paris-Sud 91405 Orsay, France. RID="c" ID="c"Present address: NAC, Faure, ZA 7131, South Africa. RID="d" ID="d"Present address: Department of Nuclear Physics, ANU, Canberra ACT 0200, Australia. Communicated by D. Schwalm     

Supersymmetry for nuclear cluster systems

A supersymmetry scheme is proposed for nuclear cluster systems. The bosonic sector of the superalgebra describes the relative motion of the clusters, while its fermionic sector is associated with their internal structure. An example of core + α configurations is discussed in which the core is a p-shell nucleus and the underlying superalgebra is U(4|12). The α-cluster states of the nuclei ²⁰Ne and ¹⁹F are analyzed and correlations between their spectra, electric quadrupole transitions, and one-nucleon transfer reactions are interpreted in terms of U(4|12) supersymmetry. Received: 14 September 2001 / Accepted: 26 October 2001     

Measurement of 2+ 1 level lifetimes in 162Yb and 162Er by fast electronic scintillation timing

Lifetime measurements for the 2⁺ ₁ levels of ¹⁶²Er and ¹⁶²Yb were obtained in β⁺/ɛ decay at the Yale Moving Tape Collector by fast electronic scintillation timing of β⁺γ coincidences. Received: 2 September 2002 / Accepted: 1 October 2002 / Published online: 4 February 2003 RID="a" ID="a"e-mail: mark.caprio@yale.edu Communicated by J. ?yst?     

Maximally aligned states in 99Ag

Excited states of ⁹⁹Ag were populated via the ⁵⁰Cr + ⁵⁸Ni (261 MeV) reaction using the NORDBALL detector array equipped with charged-particle and neutron detector systems for reaction channel separation. On the basis of the measured γγ-coincidence relations and angular distribution ratios a significantly extended level scheme has been constructed up to E _x ∼ 7.8 MeV and I = 35/2. The experimental results were described within the framework of the shell model. Candidates for states fully aligned in the πg _9/2 ^-3ν(d _5/2, g _7/2)² valence configuration space were found at 4109 and 6265 keV. Received: 18 June 2002 / Accepted: 11 October 2002 / Published online: 4 February 2003 RID="a" ID="a"e-mail: sohler@atomki.hu Communicated by J. ?yst?     

New insights into neutron-rich nuclei at high spin

With new high statistic data, new isotopes and new high-spin structures are observed in neutron-rich nuclei populated in the spontaneous fission of ²⁵²Cf. The ¹³⁵Te levels are extended, and many new levels in ^139,141Ba observed. The coexistence of collective and single particle-hole states is found in ¹³⁵Te. The N = 83 ¹³⁵Te and ¹³⁹Ba show marked differences associated with differences in their particle and hole states. New levels in ¹⁴¹Ba complete evidence for two opposite-parity doublets characteristic of stable octupole deformation. In ^114,116Pd a second backbend is observed for the first time in this mass region and the backbend in ¹¹⁸Pd occurs earlier than in ^112-116Pd because of a reduction in pairing. Gamma-type vibrational bands are seen up to 13⁺ to 15⁺ in ^104,106Mo, ^108-112Ru, and ^112-116Pd. Their behavior reflects prolate to triaxial shapes in these nuclei. The levels of ^162,164Gd are observed for the first time. As N increases toward mid-shell at 104, the moments of inertia in N = 100 ¹⁶⁴Gd show an unexpected decrease compared to N = 98 ¹⁶²Gd. The levels in ^162,164Gd form remarkable shifted identical bands with nuclei separated by 2n, 2p, α, and 2α. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: j.h.hamilton@vanderbilt.edu     

Band termination in the Z = N odd-odd nuclei <Superscript>46</Superscript>V and <Superscript>50</Superscript>Mn

The configuration-dependent cranked Nilsson-Strutinsky approach has been employed to study the properties and band structures at high spin in the Z = N odd-odd nuclei ⁴⁶V and ⁵⁰Mn. The observed bands are explained and terminating states are confirmed by the calculations. The calculated and observed bands are in good agreement without normalization, especially for terminating states. Possible bands with rotation around the intermediate axis and the effect of γ-deformation on the total energy of several interesting configurations are discussed. Received: 2 April 2002 / Accepted: 27 January 2003 / Published online: 15 April 2003     

Inelastic excitation of <Superscript>187</Superscript>Re

Excited states in ¹⁸⁷Re populated by inelastic scattering of a 500 MeV ⁸²Se beam have been studied by means of in-beam γ-ray spectroscopy. Levels built on the 5/2⁺[402] and 9/2^-[514] one-quasiparticle states were measured up to I ^π = (21/2⁺) and (21/2^-), respectively. In addition, several new levels including an isomer at 1682 keV with a half-life of 114(23) ns have been found. Quasiparticle configurations of the levels and the transition rates are discussed. Received: 12 December 2002 / Accepted: 13 March 2003 / Published online: 13 May 2003     

Rotational bands and signature inversion phenomena in πh9/2⊗νi13/2 and πi13/2⊗νi13/2 structures in odd-odd 176Ir

The ^109,111,113Rh nuclei have been produced as fission fragments in the fusion reaction ¹⁸O + ²⁰⁸Pb at 85 MeV. Their level schemes have been built from gamma-rays detected using the Euroball IV array. High-spin states of the neutron-rich ^111,113Rh nuclei have been identified for the first time. Several rotational bands with the odd proton occupying the πg _9/2, πp _1/2 and π(g _7/2/d _5/2) sub-shells have been observed. A band of low-energy transitions has been identified at excitation energy around 2 MeV in ^109,111Rh, which can be interpreted in terms of three-quasiparticle excitation, πg _9/2νh _11/2νg _7/2/d _5/2. In addition another structure built on states located at low excitation energy (608 keV in ¹¹¹Rh, 570 keV in ¹¹³Rh) points out that, as already observed in the lighter isotopes ^107,109Rh, triaxial deformation plays a role in the neutron-rich Rh isotopes well beyond the mid-shell. Received: 15 July 2002 / Accepted: 9 October 2002 / Published online: 3 December 2002 RID="a" ID="a"e-mail: porquet@csnsm.in2p3.fr RID="b" ID="b"Present address: CSNSM IN2P3-CNRS and Université Paris-Sud 91405 Orsay, France. RID="c" ID="c"Present address: CEA/Saclay, DSM/DAPNIA/SPhN, 91191 Gif-sur-Yvette Cedex, France. Communicated by D. Schwalm     

New region of deformation in the neutron-rich 60 24Cr36 and 62 24Cr38

The neutron-rich nuclei ₂₃ ^60-63V have been produced at GANIL via interactions of a 61.8A·MeV ⁷⁶Ge beam with a ⁵⁸Ni target. Beta-decay to ₂₄ ^60-63Cr has been investigated using combined β- and γ-ray spectroscopy. Half-lives of the ^60-63V nuclei have been determined, and the existence of a beta-decay isomer in the ⁶⁰V nucleus is strongly supported. The observation of low-energy 2⁺ states in ⁶⁰Cr (646keV) and ⁶²Cr (446keV) suggests that these isotopes are strongly deformed with β₂ ∼ 0.3. This is confirmed by shell model calculations which show the dominant influence of the intruder g and d orbitals to obtain low 2⁺ energies in the neutron-rich Cr isotopes. Received: 13 June 2002 / Accepted: 27 August 2002 / Published online: 17 January 2003 RID="a" ID="a"e-mail: sorlin@ipno.in2p3.fr Communicated by D. Guerreau     

Candidates for chiral doublet bands in 136Nd

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. Received: 23 May 2002 / Accepted: 30 September 2002 / Published online: 27 November 2002 RID="a" ID="a"e-mail: costel.petrache@unicam.it RID="b" ID="b"Present address: Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. RID="c" ID="c"Present address: Gesellschaft für Schwerionenforschung D-64291 Darmstadt, Germany. Communicated by C. Signorini     

High-spin states in the <Superscript>97</Superscript>Tc nucleus

High-spin states in the ⁹⁷Tc nucleus have been studied by in-beam γ-ray spectroscopy with the reaction ⁸²Se(¹⁹F,4nγ) at 68 MeV incident energy. Excited states have been observed up to about 8 MeV excitation and spin 43/2. The observed level scheme is compared with results of shell model calculations. Received: 22 November 2002 / Accepted: 23 December 2002 / Published online: 18 March 2003 RID="a" ID="a"e-mail: bucurescu@tandem.nipne.ro RID="b" ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy. RID="b" ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy. RID="b" ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy. RID="c" ID="c"Present address: Università di Padova, Padova, Italy. Communicated by C. Signorini     

Studies with one- and two-proton drip line nuclei

In recent experiments at GANIL, we studied nuclei at the one- and two-proton drip line. The production rates allowed to search for direct 2p emission in the drip line nuclei ⁴²Cr, ⁴⁵Fe, and ⁴⁹Ni. No evidence for this decay mode was found in ⁴²Cr and ⁴⁹Ni, whereas the situation stays unclear for ⁴⁵Fe due to the limited statistics. In the medium-mass region ( A = 50-70), the half-life was measured for all proton-rich nuclei in the range T _z = 0 to T _z = - 1 between Z = 27 and Z = 36. First half-lives were determined for ⁶⁰Ga, ⁶²Ge, ⁶⁴As and ⁶⁶Se. Finally, β-decay studies of the 0⁺ → 0⁺ decay of ⁶²Ga have been performed at IGISOL in Jyv?skyl?. Non-analog transitions have been observed and are compared to theoretical predictions. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: blank@cenbg.in2p3.fr