37% chance. A "dirty bomb" is a dispersal mechanism like a conventional explosive attached to a radioactive material, intended to render an affected area undesirable, impassible, or uninhabitable. Nuclear explosions (those relying on nuclear fission or fusion for their energy) do not count. Intended nuclear devices that malfunction do not count, even if they have the same effect as a dirty bomb. This question resolves NO in four years if no dirty bomb detonates anywhere in the world. This question resolves YES based on the report of a newspaper AND a reputable scientific organization. I do not expect that to be a subjective criterion, but if it appears that subjective resolution is required I will sell any shares at current market value a full day before resolving this market.