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.     

Rotational structures in 123Cs

High-spin states in ¹²³Cs, populated via the ¹⁰⁰Mo ( ²⁸Si, p4n) fusion-evaporation reaction at E _lab = 130 MeV, have been investigated employing in-beam γ-ray spectroscopic techniques. Rotational bands, built on πg _7/2, πg _9/2 and the unique-parity πh _11/2 orbitals, have been extended and evolve into bands involving rotationally aligned ν(h _11/2)² and π(h _11/2)² quasiparticles. A three-quasiparticle band based on the high-K πh _11/2 ⊗ νg _7/2 ⊗ νh _11/2 configuration has also been observed. Total Routhian Surface (TRS) calculations have been used to predict the nuclear shape parameters ( β₂, β₄, γ) for the various assigned configurations. The assigned configurations have been discussed in the framework of a microscopic theory based on the deformed Hartree-Fock (HF) and angular-momentum projection techniques.     

Observation of high spin levels in131Cs from131Ba decay

The γ- and conversion electron spectra following¹³¹Ba ε-decay are investigated, using HPGe detector and mini-orange electron spectrometer. Attention is particularly focussed on identifying weak transitions associated with low energy high spin levels in¹³¹Cs level scheme earlier inferred in reaction studies but not yet observed in¹³¹Ba decay. Our experiment identifies 15 new gammas and 6 new conversion lines in this decay. Internal conversion coefficients and multipolarities of several transitions are determined. Five new levels (3 with I^π = 7/2⁺ and one each with I^π 9/2⁺ and 11/2⁻) are introduced in the¹³¹Cs level scheme based on our observations taken together with the results from reaction studies. Spin-parity assignments to a few other levels are also suggested     

Pseudo spin gap in high‐Tc oxides observed by NMR

From the temperature dependence of the ⁶³Cu nuclear spin‐lattice relaxation rate, 1/T₁T, in the planar Cu(2) sites, it is now well established that a highly enhanced and strongly temperature dependent relaxation process due to antiferromagnetic Cu spin fluctuations exists in all of the high‐T_c’s. The data also exhibit the opening of a gap in the low‐lying magnetic excitations with an energy comparable to the superconducting gap, particularly for the so‐called low doping regime. It is also found that, irrespective of the system, the temperature at which the spin‐gap opens, T_sg, determined as the peak of 1/T₁T vs. T, has a linear decrease with increasing of the doping concentration. A spin‐gap phase diagram is proposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Observation of a decoupled band in123Cs

The methods of in-beamγ-ray spectroscopy have been used to study¹²³Cs produced by the¹¹⁵In(¹²C, 4n) reaction. Five coincident stretchedE2 transitions, previously assigned in the literature to¹²³Ba, have been identified as members of a decoupled band in¹²³Cs.     

Strong quantum spin correlations observed in atomic spin mixing

We have observed sub-Poissonian spin correlations generated by collisionally induced spin mixing in a spin-1 Bose-Einstein condensate. We measure a quantum noise reduction of -7 dB (-10 dB corrected for detection noise) below the standard quantum limit for the corresponding coherent spin states. The spin fluctuations are detected as atom number differences in the spin states using fluorescent imaging that achieves a detection noise floor of 8 atoms per spin component for a probe time of 100 μs.     

Particle-hole states at high spin in 150Dy

The level scheme of the nucleus ¹⁵⁰Dy up to spin around 40 was obtained using the reaction ¹¹⁴Cd(⁴⁰Ar, 4n). Above spins 20 to 22 — the highest obtainable from the valence nucleons — the breaking of the ¹⁴⁶Gd pproton and neutron cores occurs in separate parallel cascades.     

Shape coexistence at high spin in187Au

High-spin states in¹⁸⁷Au have been populated in the¹⁷²Yb(¹⁹F, 4n) reaction and studied with in-beam spectroscopic techniques using the “Château de Cristal” 4π-multidetector array. A comprehensive level scheme of¹⁸⁷Au has been established. Experimental band crossing frequencies and gains in alignment were deduced. Shape coexistence in¹⁸⁷Au, well established at low spin, is found to survive up to spin 57/2, and manifests itself through well separated oblate and prolate structures.     

Shape changes at high spin in 78Kr

High-spin states in ⁷⁸Kr have been studied via the ⁶³Cu (¹⁹F, 2p2n)⁷⁸Kr reaction at a beam energy of 60 MeV using the Indian National Gamma Array (INGA). In this nucleus, lifetimes have been measured upto the I^π=22⁺ level in the yrast positive-parity band and upto the I^π=15^- level in the negative-parity band using the Doppler Shift Attenuation Method (DSAM). The deduced transition quadrupole moments Q_t's are found to decrease with rotational frequency for both the bands.     

Structure of 72,74Se at high spin

Lifetimes of high spin states up to { }=22⁺ in the yrast positive parity bands have been measured to investigate the shape evolution with increasing spin in ^{72, 74}Se. The Q _t values derived from these measurements indicate that prolate shape stabilizes for ⁷²Se, while a triaxial shape develops for ⁷⁴Se at higher spins. Comparison of the observed trend in Q _t with spin for ^{72, 74}Se with that of the corresponding kryptones isotones emphasizes the stability provided by N=38 prolate shell gap even at high rotational frequency.     

Martensitic fcc-to-hcp transformation observed in xenon at high pressure

Angle-resolved x-ray diffraction patterns of Xe to 127 GPa indicate that the fcc-to-hcp transition occurs martensitically between 3 and 70 GPa in diamond-anvil cells without an intermediate phase. These data also reveal that the transition occurs by the introduction of stacking disorder in the fcc lattice at low pressure, which grows into hcp domains with increasing pressure. The small energy difference between the hcp and the fcc structures may allow the two phases to coexist over a wide pressure range. Evidence of similar stacking disorder and incipient growth of an hcp phase are also observed in solid Kr.     

Co-existing coupling schemes at high spin in 166Hf

The nucleus ¹⁶⁶Hf has been populated by the reaction ⁹⁶Zr(⁷⁴Ge,4n) using a beam energy of 310MeV. γ-rays were detected with the EUROBALL III detector array. Fourteen new normal-deformed rotational bands, of which six form coupled pairs, have been observed in ¹⁶⁶Hf. Four previously known bands have been extended to considerably higher spin, and configurations of the new bands are proposed. Two different bands have been assigned configurations involving the same orbitals at high spin. The two coupling schemes, deformation and rotation alignment, are discussed in connection with this new observation, which calls for a formulation of co-existing coupling schemes in six-quasiparticle structures involving the same orbitals at high spin.     

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