Radiological protection of the public from radioactive particles

Abstract

Radioactive particles are physically discrete sources of radioactivity that have been released into the environment as result of past accidents, incidents, and practices, and can present a hazard to members of the public by inadvertent contact with the skin and inadvertent ingestion. The historical use of radium in the luminising of aircraft components, and the subsequent decommissioning of those aircraft and associated waste disposal practices, has left a legacy of contamination, such as the radioactive particles containing Ra-226 at Dalgety Bay, Scotland. The overall aim of this thesis was to advance the current understanding of the characteristics of Ra-226 particles found in the environment and improve the assessment of radiation doses via inadvertent skin contact and inadvertent ingestion by members of the public. Ra-226 particles were physically, chemically, and radiologically characterised using optical macroscopy, scanning election microscopy with energy dispersive X-ray spectroscopy, and gamma spectrometry. Particle characteristics showed wide variation for physical appearance, size, shape, mass, density, chemical composition, and radioactivity. The absorbed dose rate from inadvertent skin contact with Ra-226 particles was assessed using Radiochromic Film (RCF) dosimetry for different skin thicknesses and averaging areas. It was found that the ICRP reference 70 µm skin thickness and nominal 1 cm 2 skin averaging area are not appropriate for the assessment of Ra-226 particles. The committed effective dose from inadvertent ingestion of Ra-226 particles was assessed using the BARGE Unified Bioaccessibility Method. It was found that the nominal ICRP f1 gastrointestinal absorption values are not appropriate for the assessment of committed effective dose from Ra-226 particles due to the wide range of bioaccessibility exhibited by the particles. The research presented in this thesis characterised and assessed the greatest number of Ra-226 particles of any study and has found that many standard assumptions used in radiological protection may not be appropriate for Ra-226 particles. The diversity of Ra-226 particle characteristics and the wide range of potential radiation doses highlights the need for site-specific characterisation and assessment studies. The recommendations from this thesis will provide a valuable input into future studies, helping to improve the radiological protection of the public from radioactive particles.