Level densities, thermodynamics and the γ-ray strength functions in 163,164Dy

Abstract

The nuclei 163,164 Dy were analyzed at the Oslo Cyclotron laboratory (OCL) by use of the so-called Oslo method. This method enables us to extract both the level density and the γ -ray strength function simultaneously from one and the same experiment. The method relies on the Brink-Axel hypothesis, which states that the primary-γ spectrum is proportional to both the level density and the γ -transmission coefficient. The γ -transmission coefficient is itself proportional to the γ -ray strength function. The level density and the γ -ray strength function provides fundamental information about nuclear structure. The level density is the starting point for extracting thermodynamic properties, whereas the γ -ray strength function characterizes the average electromagnetic properties of excited nuclei.

In this thesis results for the experimental level densities, thermodynamic properties and the γ -ray strength functions for 163,164 Dy are extracted. Several interesting features were found when studying the γ -ray strength functions. We observe an enhanced strength at around 5 MeV of excitation energy. Similar characteristics may also be recognized in other rare earth isotopes. The results for the γ -ray strength functions also indicates that the width of the pygmy resonance located in the 3 MeV region is reaction dependent.