Radiation Units

Letter to Chemical and Engineering News
Editor, C&E News: 

Elizabeth Wilson's article about radiation-resistant compounds is tainted with popular mystique in talking about the "extremely radioactive substances such as plutonium, some researchers say." [emphasis added] 

The activity of a substance is inversely proportional to its half-life.  Short half-lives imply high radioactivity; long half-lives imply low radioactivity.  

The half-life of radium is 1620 years and the half-life of the dreaded bomb-grade plutonium-239 is 24,100 years.  Therefore a micromole of radium is about 15 times as radioactive as a micromole of plutonium-239.  

It is true that some small amounts of Pu-238 (half-life 87.7 years) occur in the waste from nuclear reactors, but the the activity per mole is less than half that of Cs-137 (half-life 30.17 years), the quantity is far smaller than that of Cs-137, and the alpha radiation of the Pu is far less penetrating than that of the hard (661 keV) gamma from the cesium.  There are about 100 isotopes in radioactive waste that are more radioactive than "extremely radioactive" plutonium.  

One wonders who "some researchers" are, and why Ms.  Wilson echoes their misconceptions.  

Best regards, 
Howard Hayden 

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