In order to cause damage, alpha emitters like plutonium must come in intimate contact with a material, such as the tissues of your lungs or bones or the inside of your favorite memory chip. A billionth of a gram of plutonium inhaled or swallowed is something to seriously worry about, but you can hold a lump of the stuff in your hand as long as it is covered with a leakproof cladding or vitrified into a ceramic. It is in this sense that plutonium is extremely toxic and hazardous to the environment, while at the same time not being particularly radioactive. Heavy shielding is not required between you and it. My understanding is that the heavy metal toxicity of Pu exceeds the radioactive toxicity by several (10?) orders of magnitude. In other words, the fact that Pu is an alpha emitter is irrelevant to the risk -- it's simply like lead poisoning only several billion times worse. Simple arithmetic yields that the amount of alpha exposure from a billionth of a gram of an alpha emitter with a half-life measured in thousands of years is infinitismal. - kitten