Evidence for wobbling excitation in 161Lu

High-spin states in ¹⁶¹Lu were investigated using the EUROBALL spectrometer. A previously known triaxial superdeformed band has been extended to higher spins and a new band with similar characteristics has been discovered. Comparison to systematically occurring wobbling bands in Lu isotopes strongly suggests that these two bands represent the n_w = 0 and 1 wobbling excitations in ¹⁶¹Lu.     

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.     

Trapping guests within a nanoporous metal-organic framework through pressure-induced amorphization

The release of guest species from within a nanoporous metal-organic framework (MOF) has been inhibited by amorphization of the guest-loaded framework structure under applied pressure. Thermogravimetric analyses have shown that by amorphizing ZIF-8 following sorption of molecular I(2), a hazardous radiological byproduct of nuclear energy production, the pore apertures in the framework are sufficiently distorted to kinetically trap I(2) and improve I(2) retention. Pair distribution function (PDF) analysis indicates that the local structure of the captive I(2) remains essentially unchanged upon amorphization of the framework, with the amorphization occurring under the same conditions for the vacant and guest-loaded framework. The low, accessible pressure range needed to effect this change in desorption is much lower than in tradition sorbents such as zeolites, opening the possibility for new molecular capture, interim storage, or controlled release applications.     

Hydration structures of U(III) and U(IV) ions from ab initio molecular dynamics simulations

We apply DFT+U-based ab initio molecular dynamics simulations to study the hydration structures of U(III) and U(IV) ions, pertinent to redox reactions associated with uranium salts in aqueous media. U(III) is predicted to be coordinated to 8 water molecules, while U(IV) has a hydration number between 7 and 8. At least one of the innershell water molecules of the hydrated U(IV) complex becomes spontaneously deprotonated. As a result, the U(IV)-O pair correlation function exhibits a satellite peak at 2.15 A? associated with the shorter U(IV)-(OH(-)) bond. This feature is not accounted for in analysis of extended x-ray absorption fine structure and x-ray adsorption near edge structure measurements, which yield higher estimates of U(IV) hydration numbers. This suggests that it may be useful to include the effect of possible hydrolysis in future interpretation of experiments, especially when the experimental pH is close to the reported hydrolysis equilibrium constant value.     

Magnetic properties of the υj15/2 intruder orbital in the superdeformed minimum of 197Pb

This work has established eight cross-talk transitions between the two signature partner superdeformed (SD) bands in ¹⁹⁷Pb with the EUROBALL IV spectrometer. Directional correlations from oriented states measurements confirm the ΔI = 1 character of these transitions. The flat behaviour of the dynamical moment of inertia and the agreement between the experimental and microscopic HF+BCS values of (g _K - g _R)K/Q ₀ suggest that the configuration of the SD bands is based upon the υ[752]5/2^- neutron intruder orbital. The derived effective spin gyromagnetic factor g _s ^eff is found to be not quenched, and is close to the theoretical g _s ^free value. Received: 14 June 2000 / Accepted: 14 September 2000