Thorium in the workplace measurement intercomparison

The monitoring of radionuclides in the nuclear industry has been recognized as the most straightforward way of assessing health and safety issues associated with the exposure of the workforce to potentially harmful radiation doses. Much of this is achieved by measurements in the workplace itself and by the bioassay and monitoring of workers in the industry. However, there also exists a significant ‘non-nuclear’ industry where workers are exposed to radioactive materials, for example where this involves thorium, which is made wide use of in the aerospace and other high technology industries. As such work involves the processing of thorium bearing materials, the workforce is potentially exposed to 232Th and its daughter nuclides. Thus, to monitor the workforce effectively, it is important to be able to measure both 232Th and the decay products of 232Th where they are in an unknown state of radioactive equilibrium and this is where monitoring laboratories may experience some difficulty. Accordingly, the Health and Safety Laboratory in the UK has organized a EC wide project on the monitoring of thorium in the ‘non-nuclear’ workplace; this project is currently ongoing. We report the results of the first intercomparison of this project involving two solutions of 232Th, one in radioactive equilibrium and one not in equilibrium with its daughters. The results are presented with some comments on how this intercomparison has progressed and how these first results will inform the rest of the project.