Microscopic quasiparticle-phonon model in the study of the beta decay of Cd-115

Abstract

This master’s thesis concerns the use of the microscopic quasiparticle-phonon model in the study of the beta minus decay of Cd-115. The first part of this text concentrates on the theoretical description of nearly spherical open-shell odd-A nuclei by using the microscopic quasiparticle-phonon model. The treatment of the subject is far from exhaustive but all the necessary relations needed in the practical application of the formalism are provided in the text.

The second part provides the theory that is needed for the study of beta minus decay. In addition to the general theory of forbidden beta minus decay, also the greatly simplified case of allowed transitions are discussed. Again rather than providing a fully comprehensive treatment of the subject, a more streamlined approach is adopted. All the various relations that are needed in the practical application of the theory are provided in the text.

Finally, in the third and final part of the text the above theoretical framework is applied to the beta minus decay of Cd-115. In addition to the ground state transitions of Cd-115, it is also possible to study the transitions coming from the first excitation state due to its isomeric character. Because of the various possible ways of carrying out the fitting of the QRPA phonons, several sets of calculated partial half-lives are obtained. The calculated partial half-lives are compared to experimental results. For several transitions values that are fairly close to the experimental ones can be found. However, in many cases there are large disrepancies between the two. Some of the transitions seem also to be very sensitive to the adjustments made to the QRPA phonons. The effect of varying the nucleon spin-orbit interaction strength was studied as an additional exercise.