Chemical effects of the irradiation of solids

Cairns, James A. (1966) Chemical effects of the irradiation of solids. PhD thesis, University of Glasgow.

Abstract

This study provides an insight into the sequence of events which take place in crystalline alkali halides following thermal neutron absorption and prompt gamma-ray emission. The object of the work was to clarify certain aspects of "hot atom" chemistry by utilising current concepts of radiation damage theory.

The system chosen for this investigation was potassium iodide, in the form of single crystals. It was postulated that (n,g) reactions involving the iodine atoms would lead to a series of focused collision sequences in the anion lattice, causing ejection of atomic iodine from the crystal surfaces in certain preferred directions. The problem of detecting these chemically minute amounts of recoiled iodine was solved by having the potassium iodide surfaces labelled with I131, an isotope with a convenient half-life, which would not itself be produced by thermal neutron activation of potassium iodide.

Using the facilities of the Scottish Research Reactor Centre, a variety of experimental techniques, viz., gamma-ray spectrometry, autoradiography, ionic conductivity, etc., has proved that ejection of iodine atoms from the surfaces of single crystals of potassium iodide is preferentially initiated by thermal neutrons, as predicted, and is accompanied by modest lattice damage, in agreement with the proposed mechanism. It has also been shown that the influence of fast neutrons is to cause more extensive lattice damage and consequently fewer collision sequences. In addition, an inverse relationship between crystal surface roughness and yield of ejected iodine has been established.

Various collectors have been developed for the purpose of capturing and localising the energetic iodine atoms recoiled from the crystal surfaces on irradiation; the most successful ones have been palladium/polystyrene, butadiene-acrylonitrile, and activated charcoal/aluminium. The first two types of collector have led to the observation of a remarkable distortion in the gamma-ray spectra of I131 recoil atoms when irradiations were conducted at -78°C. A large volume of experimental evidence has been accumulated in elucidating this phenomenon.

When quantitative irradiations and studies of yields were made, it became apparent that the amount of iodine recoiled from the surfaces of the crystals was too high to be accounted for on the basis of mere thermal neutron absorption and prompt gamma-ray emission, causing I128 recoil. It is explained, on the basis of theoretical approaches, how this large number of released atoms may be due to a process of multiple ionization, caused by internal conversion and secondary electron emission following thermal neutron capture. This conclusion was strengthened by taking into account the results of irradiations conducted in a flux of gamma-rays. Should it prove to be correct, it would constitute a most valuable insight into the (n,γ) process in this system.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Nuclear chemistry.
• Subjects: Q Science > QD Chemistry
• Colleges/Schools: College of Science and Engineering > School of Chemistry
• Date of Award: 1966
• Depositing User: Enlighten Team
• Unique ID: glathesis:1966-77199
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jan 2020 11:53
• Last Modified: 02 Feb 2023 13:35
• Thesis DOI: 10.5525/gla.thesis.77199
• URI: https://theses.gla.ac.uk/id/eprint/77199