Gamma ray emission tomography and angular correlation measurements to study the distribution and binding site of selenium

• Main Author: Dhani, Anwar
• Published: University of Surrey 1989
• Subjects: 539.7; Nuclear physics & particle accelerators
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234481

The distribution of 75Se in tissue equivalent materials was investigated employing Gamma ray Emission Tomography with a rectilinear scanner utilizing NaI(Tl) and BGO detectors. The reconstructed images, using Filtered Back Projection and Iterative techniques were presented in 2D colour and 3D representations. Using a lead collimator of aperture 1.5x20 mm and 70 length, the distribution of selenium with variation of volume and concentration was examined and clearly seen. Several corrections such as background, scattering, attenuation compensation and X-ray characteristic suppression, were performed to improve the quality of the images which was evaluated in terms of the fidelity factor. The possibility of quantifying an image was considered with regard to spatial resolution and least detectable concentration. The spatial resolution was measured using two small vials containing the same concentration of selenium, the value obtained was the same as the width of the collimator aperture. The value of the least detectable concentration of selenium however, was difficult to find, due to the many ambiguous factors involved. The binding site of selenium which is based on quadrupole interaction with the surrounding electric field, was investigated employing Perturbed Angular Correlation (PAC) experiments using NaI(Tl) and BaF2 detectors. Using NaI(Tl) detectors, it was difficult to observe the perturbation, due to the poor time resolution. The BaF2 detector according to the literatures has a shorter light emission decay time constant (0.6 ns), suggested that a better time resolution than that found with the NaI(Tl) detectors could be obtained. A Perturbed Angular Correlation experiment employing BaF2 detectors and a fast-slow coincidence system was set up. The time differential PAC of selenium in solution showed an unperturbed angular correlation pattern. The main problem is the very short half life of the intermediate state of 75Se (0.3 ns), making it difficult to observe the perturbation effect. The time resolution of the system (5.4 ns) will need to be improved by an order of magnitude or more for the investigations to continue.