Multiple Nucleon Emission From 232Th Following High Energy Photo-Excitation

High energy physics, Nuclear physics and radiation, High temperature physics

Miller, Gary John

University:University of Glasgow

关键词: High energy physics, Nuclear physics and radiation, High temperature physics;   

Others  :  http://theses.gla.ac.uk/77549/1/10995597.pdf

来源: University of Glasgow

【 摘 要 】

New results are presented on the multiple emission of nucleons from 232Th following photo-excitation in the energy range 40-150 MeV. Using activation techniques, the cross-sections for 11 separate (gamma, xnyp) photoreactions have been determined from the residual alpha-activity of their reaction products. In the course of this investigation, improved half-lives have also been measured for several of the actinide nuclides studied. Photoreaction cross-sections, obtained from the electron and bremsstrahlung yield curves, have been compared with the predictions of the intranuclear cascade and hybrid exciton models for precompound nuclear decay. The photodisintegration models in their present form, while reproducing the general trends of the measured cross-sections, appear to underestimate the importance of precompound fast particle emission during the nuclear de-excitation sequence which follows photon absorption. Necessary improvements to these models, regarding their application to photonuclear interactions, are discussed. The importance of fission competition in the nuclear disintegration process has also been demonstrated and present estimations of the parameters governing fission decay in this energy domain, are shown to be reasonably valid. Comparisons of the real and virtual photon data gathered in this experiment suggest that present calculations of the virtual photon spectra, made in second order Born approximation, underestimate the E1 intensity for nuclei in this mass and energy range. The need for a virtual photon formalism which incorporates a full treatment of both nuclear size and charge effects is emphasised. This new data greatly extends the information available on photodisintegration in heavy nuclei and provides a useful testing ground for theoretical treatments of the final-state interactions and absorption mechanism associated with photonuclear processes at these energies.