Radionuclide deposition from the Chernobyl cloud

The accident at the Chernobyl nuclear power station in the Soviet Union created a cloud of radioactivity that affected a surprisingly large area of Europe. This letter concentrates on the main passage of this cloud over the United Kingdom and presents some results of preliminary investigations into the collected data on radioactivity levels in the air, in rain water, on grass and in milk, and attempts to link the time variations of these levels to meteorological conditions. In particular, we report that high levels measured on grass are linked to to heavy rainfalls associated with thunderstorms embedded in the radioactive cloud. The accident is believed to have begun at 01: 23 local time on Saturday 26 April (20:23 GMT on Friday 25 April) and to have ended on the following Wednesday or Thursday. By the Monday, countries throughout Europe had been alerted and possible trajectories of the plume were being estimated, based on standard meteorological data. In many cases, analyses and forecasts from numerical weather prediction models were being used. Trajectories calculated at the Meteorological Office early in the week indicated a possible risk to the United Kingdom, and this possibility was strengthened when, on Wednesday, enhanced radiation levels were reported in northern Italy, indicating a first arrival in the United Kingdom on Friday 2 May. Since then, more thorough analyses of the cloud movement have been carried out at the Meteorological Office and at many other centres throughout Europe, and the most probable path of the cloud that affected the United Kingdom is shown