Spin alignment in the particle-rotor and cranking models

It is shown that the cranking model normally gives a smaller rotation-aligned spin for an odd quasiparticle than the particle-rotor model, especially at low rotational frequencies. The basic reason is found to be that the rotational frequency vector of the cranking model is “sharp”. This is an unphysical model property, and in the presence of a particle whose rotational motion is partly decoupled from the rotational motion of the average field its consequences become serious. A “sharp” rotational frequency corresponds to a neglect of the recoil effect that establishes coherence between the motion of the decoupled nucleon and the other nucleons and therefore is a prerequisite for the conservation of angular momentum. In conclusion the cranking model cannot be invoked to explain the so-called “Coriolis attenuation”, relative to the particle-rotor model, that is observed experimentally. Particle-rotor calculations are carried out into the backbending region of some well-deformed rare-earth nuclei, and the results indicate that the “Coriolis attenuation” effect is weak or absent at high rotational frequencies. However, the experimental $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$, unfavoured band of ¹⁶⁷Yb is found to exhibit an anomalous “downbending” behaviour.     

Rotational bands on few-particle excitations of very high spin

An RPA formalism is developed to investigate the existence and properties of slow collective rotation around a non-symmetric axis, when there already exists a large angular momentum K along the symmetry axis built up by aligned single-particle spins. Both repeatability and E2 collectivity are required to distinguish the collective rotational-like solutions from the others, which may come lower in energy. First the formalism is applied to bands on high-K isomers in the well-deformed nucleus ¹⁷⁹Hf, where the rotational-model picture is reproduced for intermediate K-values in agreement with experiment. At high K the collectivity is suppressed even more than the diminishing vector-coupling coefficient of the rotational model would suggest, but the repeatability actually improves. The moment of inertia is predicted to remain substantially smaller than the rigid-body value, so the bands slope up steeply from the yrast line at spins where pairing effects are gone. A second application is to the initially spherical nucleus ²¹²Rn, which is believed to acquire an oblate deformation that increases steadily with K due to the oblate shape of the aligned orbitals. In this case the rotational-like excitations also exist but are still less favoured than in ¹⁷⁶Hf, even at comparable deformations. Some collective states may come closer to the average yrast trend, but they have lower repeatability because they are more like dressed single-particle excitations. The main differences between the two nuclei studied is interpreted as a general consequence of their different shell structure.     

The improved convergent syntheses of arecolones and isoarecolone

Good yields of arecolone and isoarecolone were obtained by treating the N,O-dimethylamides of arecaidine and isoarecaidine, respectively, with methylmagnesium chloride. Other substituted arecolones were synthesized by this same strategy.     

Counting and measuring particles sized from soot to pollen

For number concentration measurements of superfine particles a condensation nucleus counter （CNC） is frequently used. The combination of a new CNC module with a white light aerosol spectrometer and a passive collector makes possible accurate time-resolved determination of particle number within the overall size range of 10 nm to 40 μm and at concentrations up to 10^5 particles/cm^3. With the aerosol spectrometer a high time-resolved particle size determination is also possible in the size range of 0.3-40 μm up to the same high number concentrations of 10^5 particles/cm^3.     

Collective quadrupole dynamics and the band structure of the nucleus 127Cs

Excited states of ¹²⁷₅₅Cs were populated in the ¹²⁷I(α, 4n)¹²⁷Cs reaction. Singles, prompt and delayed γ-ray spectra, γγ coincidence spectra, angular distributions and excitation functions were measured, and negative and positive parity bands established. The h_{$\text{11}\text{2}$} families of excited levels in ^{127, 129}Cs and ¹³³La were reproduced by core-particle coupling calculations, regardless of whether the cores were taken to be rigid triaxial rotors or to have all five quadrupole degrees of freedom. The hamiltonians for the latter case were based on microscopic calculations which attribute an important role to the γ-dependence of the mass functions for collective quadrupole motion. From a core-quasiparticle analysis of the positive-parity levels in ¹²⁷Cs, indications of a “Coriolis attenuation” anomaly were inferred.     

On the stability of the transeinsteinium elements

We calculate ground-state properties of nuclei in the Z≧100 region. The most stable superheavy elements are predicted for lower neutron number than in previous investigations, namely ₁₁₀ ²⁸⁸ X and ₁₁₀ ²⁹⁰ X, both with a calculated half-life of around 200 days. A new feature is a local minimum in the ground-state shell correction at Z=110 andN=162. Elements in this region are therefore expected to show increased stability relative to some earlier expectations.