γ-Ray Absorption Cross Sections of F¹⁹, Mg²⁴, Al²⁷, and Ca⁴⁰ in the Giant Dipole Resonance Region

Abstract

A detailed investigation of the interactions of high-energy γ-rays with nuclei can give extensive and reliable information about the properties of highly-excited nuclear states. In principle, the theoretical interpretation of these studies is simpler than the interpretation of results obtained from studies of nucleon and nucleon system interactions with nuclei because the properties of the electromagnetic interaction are well known and reliably explained by theory. From the point of view of interpretation of results, studies of the nuclear γ-ray absorption section are of great interest because the requirement for inclusion of supplemental information about the properties of the channel along which the decay of the excited nucleus goes is eliminated in that case. However, the smallness of the cross section and the need for working with a continuous bremsstrahlung spectrum create serious difficulties in performing such experiments. These difficulties are compounded by the requirement for good energy resolution and high statistical accuracy because there is considerable interest in data on absorption cross section structure in addition to data on the integral characteristics of the cross section. In practice, such experiments can only be performed with light nuclei where the level densities are low. All this is why, at the start of the experiments to be discussed (middle of 1962), sufficiently accurate measurements of the absorption cross section which could be reliably compared with theoretical data had been completed only for C¹² and O¹⁶.

Dissertation offered in satisfaction of the requirements for the scientific degree of candidate in the physical and mathematical sciences. Defended on May 26, 1965, at the MGU Research Institute for Nuclear Physics (abridged version).