For many environmentalists, exposure to man-made radiation is one of the biggest eco-threats around.  But according to data from a special United Nations scientific committee, scares about exposure from nuclear power and other man-made sources should be melted down.  The committee’s massive new report, entitled sources and effects of ionizing radiation, notes for example, that while most people around the world are exposed to about 40 millirems of man made radiation each year, they are exposed to six times that amount annually from natural sources.  When you also consider that exposure from just one typical chest x-ray is 500 times greater than that from nuclear power plant operations, it sounds like a chain reaction of evidence against anti-nuclear hype.