Jeudi 26 mars 2009, à 16h00
Two new representations of the data on rotational nuclei are suggested. The first is reference-free, and the second arises from the natural VMI (Variable Moment of Inertia) reference corresponding to the ground-state band of the system. As such neither contains any free parameters. By defining a ‘configuration spin and energy’, it is shown that the ground-band reference has previously been incorrectly applied. Its correct use allows a more complete description of the changes associated with the first, and higher, band crossings. These representations are applied to discuss the nature of the AB crossing along even-even isotopic chains in the rare-earth region. Neighbouring odd-even nuclei are also discussed.
Although an yrast condition is exploited to derive some of the relevant relationships, they can be equally well applied to higher rotational bands since their energies are also minimised (subject to their wavefunctions being orthogonal to those of lower bands). A study of excited bands shows that the VMI configuration, originally introduced to explain properties at the lowest angular momenta, may also play an important role at higher spins, in particular in superdeformed nuclei in the mass-190 region.