This is a reconstruction of the Chernobyl radioactive plume by the French Government's official agency on radiation and nuclear matters, the Institut de Radioprotection et Surete Nucleaire.
It is based on weather patterns for the time period April 26 to May 6 when the fire was burning inside the stricken reactor, and on known Cs-137 measurements.
It is a remarkably graphic illustration of the huge extent of the radioactive contamination of East and West Europe (and eventually the rest of the Northern Hemisphere) by the Chernobyl catastrophe.
After you have opened this page please wait for 1 or 2 minutes while the film (15 MB) is downloaded to your computer: it then starts automatically. Link to file.