Eksperimentele bepaling van energievlakbreedtes in die kerne 79Br en 81Br

Abstract

The dissertation discusses the experimental determination of the level widths and mean lifetimes of the 1.07 MeV and 1.10 MeV nuclear energy levels in the stable isotopes of bromine ( 79Br, 81 Br). The technique of resonance fluorescence has been used and in particular the resonant scattering of Compton scattered gamma rays has been observed. The primary radiation originated from a 4700 curie source of 60co. In the first sequence of experiments a NaI(Tl) scintillation counter was used as detector, but later a 20 cm3 Ge(Li) solid state detector was employed. In chapter I of the dissertation the definition of resonance fluorescence will be found . A discussion of the interaction between gamma rays and matter is also given. Equations relevant to a discussion of transition probabilities and level widths are summarized. In chapter II the dissertation discusses the concepts of resonance absorption and resonance scattering of gamma radiation in matter . Expressions for the yield of resonantly scattered gamma quanta are derived and the experimental technique known as self-absorption is discussed. Chapter III is a discussion of the experimental arrangements which were used in the determinations of lifetimes. In chapter IV the lifetimes which have been determined by measurements with the NaI detector have been recorded . Since no data on the spins of the 1.07 MeV and 1.10 MeV levels were available, lifetimes for various spin assignments of the two excited states have been calculated in this chapter . The fact that it is not known in which isotope the particular level occurs, was also taken into consideration . In chapter V the results obtained from measurements with the Ge(Li) detector are presented and the results derived from the respective experiments with the two detectors are discussed . An explanation of how the exact energies of the 1.07 MeV and 1. 10 MeV levels in bromine have been determined, is given in chapter VI .