Mark Cunningham

The formalism of the Interacting Boson-Fermion Model permits the calculation of the properties of the low-lying collective states in odd-mass nuclei. Transitional nuclei, which are difficult to understand in terms of other nuclear models, are easily dealt with in this framework. Additionally, the model allows the treatment of cases in which several single-particle degrees of freedom are important. Moreover, the mixing of these various degrees of freedom need not be weak. We present here the application of this formalism to the study of the light isotopes of xenon and barium.

We begin with an analysis of the negative parity states in these nuclei in terms of the single j-shell approximation. Energy spectra and electromagnetic moments and transitions are discussed for a large set of nuclei, assuming that the odd neutron occupies the 1h(,11/2) neutron orbital. The results of these calculations indicate that while many of the properties of these nuclei can be reproduced by this simple approximation, there are features which cannot. Thus in an attempt to improve the description of these states, we repeat the calculations, including the 2f(,7/2) and 1h(,9/2) levels. These two levels come from the next major shell, but could have considerable influence on the low-lying structure of these nuclei if the mixing matrix elements are large.

Finally, the positive parity states in these nuclei are analyzed, incorporating the 3s(,1/2), 2d(,3/2), 2d(,5/2) and 1g(,7/2) single particle levels. These four levels are the remaining levels of the 50-82 neutron major shell, and all four are important to completely describe the low-lying states in these nuclei. Again, we report the results of the calculation of energy levels and electromagnetic moments and transitions for these positive parity states.