Characteristics of Ra-226 particles from legacy contamination and implications for radiological protection

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. 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 aim of this research was to physically, chemically, and radiologically characterise Ra-226 particles from Dalgety Bay and consider the implications for radiological protection of the public. Physical characterisation measured particle size and shape using optical macroscopy with image analysis, measured particle mass, and calculated particle density, as well as general observations on their physical appearance. Chemical characterisation used scanning electron microscopy with energy dispersive X-ray spectroscopy to measure surface elemental composition, and gamma spectrometry was used to measure the activities of Ra-226 and its gamma-emitting daughter radionuclides. Qualitative observations on visual appearance indicated there were five distinct subpopulations, and measurements of size, shape and density varied widely. A wide range of surface chemical compositions were observed, and evidence of their estuarine origin was visible in the form of sand grains and salt deposits. Ra-226, Pb-214, Bi-214 and Pb-210 were detected in all samples with activities over several orders of magnitude and varying degrees of secular equilibrium. Two original aircraft artefacts were also included in the investigation, comparison with which showed the particles and artefacts differed in their characteristics, indicating that the source material has undergone alteration. The diversity of particle characteristics has implications for the radiological protection of the public from Ra-226 particles including pathways of exposure, assessment of radiation dose, and longevity in the environment.