New insight in the level structure of <Superscript>153</Superscript>Er

The high-spin level structure of the ¹⁵³Er nucleus has been reinvestigated by in-beam γ-ray and electron spectroscopy with (¹⁴N,pxn) reaction. Excitation energies, spin and parity assignments are unambiguously established for the two lowest isomers T _1/2≃ 380 ns and T_1/2\simeq 10 ns. The characteristics of the third one (T _1/2≃ 250 ns) at 5.2 MeV are still questionable but its main decay modes are better known. An extension of the level scheme is proposed up to 8.4 MeV.Experimental results have been discussed in terms of shell model multiplets and compared with the other structures observed in N=85 neighbouring nuclei. Received: 8 November 1999 / Revised version: 13 December 1999     

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     

Signature inversion in the yrare band of <Superscript>119</Superscript>Xe

Excited states of the ¹¹⁹Xe nucleus have been studied by using in-beam γ-ray spectroscopy with the ¹⁰⁷Ag ( ¹⁶O, p3n) ¹¹⁹Xe fusion-evaporation reaction at a beam energy of 85 MeV. The level scheme of ¹¹⁹Xe has been derived from γ-γ coincidence and γ-γ angular correlation analyses. We have, for the first time, established the second negative-parity favored and unfavored states built on the 11/2^- state, namely the yrare rotational bands in ¹¹⁹Xe. In contrast to the behavior of the yrast bands where the favored states are lying lower in energy, the yrare favored states were observed to lie above the unfavored band. Such a signature inversion in ¹¹⁹Xe is changed to be normal at I = 12?. Received: 8 January 2002 / Accepted: 18 April 2002     

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     

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     

Low-spin states in <Superscript>182</Superscript>Os and K<Superscript>π</Superscript> = 0<Superscript>+</Superscript>, 2<Superscript>+</Superscript> excited bands

Excited states in ¹⁸²Os were populated by the β⁺/EC decay of ¹⁸²Ir following mass separation. Gamma-ray and conversion electron spectroscopy techniques were employed. Monopole (E0) contributions were determined in transitions populating the ground-state band. A systematic study of the low-spin structures in the Os isotopes is presented and a detailed analysis in the framework of a microscopic configuration mixing approach is performed.     

New states and γ-transitions in 209Bi observed in the (3He, d*γγ)-subcoulomb-reaction

High-spin states in ¹⁴³Pm have been investigated via the ¹²⁸Te(¹⁹F,4nγ)¹⁴³Pm reaction using techniques of in-beam γ-spectroscopy. γ-ray singles, γ-γ coincidences, γ-ray anisotropies and DCO ratios have been measured. Based on these measurements, the level scheme of ¹⁴³Pm has been extended up to an excitation energy of 10535.4 keV, including 48 new γ-rays deexciting 28 new levels. The yrast levels in ¹⁴³Pm can be understood qualitatively in the framework of a weak-coupling model. Received: 10 July 2000 / Accepted: 12 October 2000     

Beta decay of 101Sn

The β decay of the very neutron-deficient isotope ¹⁰¹Sn was studied at the GSI on-line mass separator using silicon detectors for recording charged particles and germanium detectors for γ-ray spectroscopy. Based on the β-delayed proton data the production cross-section of ¹⁰¹Sn in the ⁵⁰Cr + ⁵⁸Ni fusion-evaporation reaction was determined to be about 60nb. The half-life of ¹⁰¹Sn was measured to be 1.9(3)s. For the first time β-delayed γ-rays of ¹⁰¹Sn were tentatively identified, yielding weak evidence for a cascade of 352 and 1065keV transitions in ¹⁰¹In. The results for the ¹⁰¹Sn decay as well as those from previous work on the ¹⁰³Sn decay are discussed by comparing them to predictions obtained from shell model calculations employing a new interaction in the ⁸⁸Sr to ¹³²Sn model space.     

Indication for hyperdeformed cluster states in <Superscript>233</Superscript>Th

An activation technique was used to investigate relative yields of fission products from the reaction ²³²Th(n, f ) for neutron energies between 1.3 and 1.8MeV covering the region around the first hyperdeformed resonances. Intensities of characteristic γ-ray transitions were analyzed to search for changes in the mass distribution for neutron energies corresponding to the resonances and below the resonances. Relative increases in yield between 7 and 23% are observed for A ≈ 100 and 132 in the resonance region around 1.6MeV. It is proposed that the yield enhancement of daughter nuclei of the preformed fragments ¹³²Sn and ¹⁰¹Zr arises from cold fission of a di-cluster configuration. The experimental results support theoretical predictions for the existence of hyperdeformed octupole shapes based on the di-nuclear configuration ¹³²Sn + ¹⁰¹Zr.     

High-spin levels in 147Tb

The high-spin states of ¹⁴⁷Tb have been studied with regard to their spins. The data were obtained by in-beam γ-ray spectroscopy using the reaction ¹²⁰Sn(³¹P,4n)¹⁴⁷Tb at 152 MeV performed at the Osiris spectrometer in Berlin. We obtained multipole mixing ratios for 60 transitions, and level spins up to 67/2ħ are introduced. Received: 30 March 1998     

High-spin isomers in 183Os

High-spin states in ¹⁸³Os have been studied by means of in-beam γ-ray spectroscopy. Two isomers with I ^π= ((43/2)⁻) and (43/2)⁺ have been identified at excitation energies of E _x = 5.068 and 5.168 MeV. The half-lives are determined as T _1/2= 27 ± 3 and 24 ± 2 ns. Received: 22 December 1997     

Fragment dependence of high energy γ-ray emission in the spontaneous fission of 252Cf

The high energy γ-ray emission accompanying the spontaneous fission of ²⁵²Cf has been measured in coincidence with individual fission fragments selected by discrete γ-ray transitions. The enhancement of the γ-ray emission probability in the energy range E_γ= 3–8 MeV has been observed for the fission fragments in the region of nearly symmetric mass splitting, confirming results reported in previous investigations. The γ-γ coincidence technique employed in the present work clearly demonstrate that the major contribution to this enhancement is caused by the fission channels where one fragment is near to the N= 82 or Z= 50 shell closures. The high energy γ-ray emission probability does not show any significant dependence on the number of neutrons emitted in the fission process, supporting the hypothesis that high energy γ-rays are mainly emitted from the fragments after the neutron evaporation. Received: 22 December 1998     

Band structures in 108In

High spin states in ¹⁰⁸In have been established upto ∼ 8 MeV in excitation energy and to a tentative spin of (23⁻). The data were obtained by in-beam γ-ray spectroscopy using the reaction ⁹³Nb(¹⁹F, p3n)¹⁰⁸In at a beam energy of 86 MeV. Four sequences of dipole bands and a normal rotational band of E2 γ-transitions have been placed in the level scheme. Received: 16 June 1998     

A new high-spin isomer in 145Sm

A new high-spin isomer in ¹⁴⁵Sm was observed by in-beam γ-ray spectroscopy with the reaction ¹²²Sn(²⁷Al,3np) at 127 MeV performed at the Nordball multi-detector array in Roskilde. The excitation energy of the isomer was determined to be E _x= 11147 keV, and using the generalized centroid-shift method its half-life was found to be T _1/2= (7.4 ± 1.0) ns. Received: 23 October 1998     

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     

On the unusual properties of the 282 keV state in <Superscript>135</Superscript>Sb

Recently the first excited state in ¹³⁵Sb has been observed at the unexpectedly low excitation energy of only 282keV and interpreted as mainly d _5/2 proton coupled to the ¹³⁴Sn core. Based on theoretical considerations it was suggested that its low excitation energy is related to a relative shift of the proton d _5/2 and g _7/2 orbits induced by the neutron excess. We have measured the lifetime of the 282keV state by the advanced time-delayed βγγ(t) method. The measured half-life, T _1/2 = 6.1(4)ns, yields exceptionally low limits of B(M1;5/2₁ ⁺→7/2₁ ⁺)≤3.0×10^-4 μ ² _N and B(E2;5/2₁ ⁺→7/2₁ ⁺)≤54e ² fm ⁴. These strongly hindered M1 and slow E2 transition rates are similar to those for the transition de-populating the first excited state at 405keV in ²¹¹Bi. Results of shell model calculations with realistic interactions are presented. The M1 decay rate was found to be extremely sensistive both to the wave function and to the M1 effective operator.     

Inelastic scattering on 12Be and disappearance of the N = 8 magic number

Experimental studies on in-beam γ-ray spectroscopy using a ¹²Be radioactive beam are presented. Inelastic scattering of the neutron-rich ¹²Be nucleus on ²⁰⁸Pb, ¹²C, and (CH₂)_n targets has been studied by measuring de-excitation γ-rays in coincidence with scattered particles. The level schemes and transition probabilities are determined for low-lying excited states in ¹²Be. The present paper presents a brief review of the spectroscopic results, which may be associated with the N = 8 shell quenching near the drip line. Received: 1 May 2001 / Accepted: 4 December 2001     

Level structure of 123Cs observed from 123Ba decay and described using the IBFM and CQPC models

The decay of ¹²³Ba to ¹²³Cs has been studied with mass-separated sources. Singles spectra of γ-rays, X-rays and conversion electrons as well as γ - γ - t, γ - e ⁻ - t, and X - e ⁻ - t coincidences were recorded. A level scheme of ¹²³Cs has been constructed including 26 new excited states and 82 transitions. The existence of a I ^π = 11/2⁻, T _1/2 = 1.7 s isomer, bandhead of the h _11/2 band, is confirmed. Its excitation energy equals 156.3 keV. A new T _1/2 = 114 ns isomer has been established at 232 keV using the in-beam recoil catcher technique. It is assigned to the I ^π = 9/2⁺ bandhead of the gpg _9/2 band. Collective bands based on the 1/2⁺ ground state and first 3/2⁺ excited state are proposed. The level structure is described in the frame of the interacting boson-fermion and core-quasiparticle coupling models.     

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     

Beta decay of 94Pd and of the 71 s isomer of 94Rh

The β decay of ⁹⁴Pd and of the 71s isomer of ⁹⁴Rh was investigated by using total γ-ray absorption techniques. Several levels in ⁹⁴Rh are established, including a new low-lying isomer characterized by a half-life of 0.48(3)μs and a de-exciting transition of 55keV. E2 multipolarity is determined for this transition by measuring the intensities of its γ-rays and the characteristic X-rays from its electron conversion. On the basis of the measured reduced β-decay transition rates to known ⁹⁴Ru levels and shell model considerations, the spin-parity of the 71s and the 0.48μs isomers of ⁹⁴Rh is assigned to be (4⁺) and (2⁺), respectively. The β-decay strength distributions measured for ⁹⁴Pd and the 71s isomer of ⁹⁴Rh yield Q _EC values of 6700(320) and 9750(320)keV for these decays and give evidence for the population of those states below and above the magic N = 50 gap that belong to both components of the 0g spin-orbit doublet.