Radiation Imaging with Caesium Bromide Storage Phosphors

Abstract

This thesis is centred on the development of a new method to prepare semitransparent CsBr:Eu²⁺ imaging plates for high resolution X-ray radiography. Methods of characterising the performance of these plates, and their application to dual energy imaging and neutron imaging are discussed. The basic preparation method, based on high-pressure uniaxial compression of powder mixtures of CsBr and EuBr₂, produces imaging plates which show good transparency and resolution. These imaging plates have a conversion efficiency of 1.5 pJmR⁻¹mm⁻³ compared to 5.1 pJmR⁻¹mm⁻³ for a commercial needle imaging plate. Water is found to play a critical role in the photostimulated luminescence activation in CsBr:Eu²⁺ storage phosphors, and imaging plates subsequently hydrated at room temperature have an increased conversion efficiency of up to 11 pJmR⁻¹mm⁻³, better than the commercial material. A model has been suggested for the generation of the PSL active site in the imaging plates based on thermomechanical sintering and water-induced crystal regrowth. A precise method for determining the conversion efficiency and stimulation energy of X-ray storage phosphor materials using an integrating sphere has been developed and used to characterise the materials developed in this thesis. A novel read-out method for storage phosphor imaging plates based on flood illumination and a semi-professional digital camera has also been developed and tested. Good quality X-ray images are obtained and the method shows excellent promise as a low-cost, portable X-ray imaging system. A stratified detector using CsBr imaging plates has been developed for use in dual-energy imaging. Results suggest that it is possible to perform dual-energy imaging with this structure. CsBr:Eu²⁺ imaging plates have been produced with added neutron converters for use as thermal neutron imaging plates. An imaging plate with 5 % ¹ºB₂O₃ added as a neutron converter has a PSL output 50 % that of a commercial neutron imaging plate. Neutron imaging with these imaging plates has been successfully demonstrated.