With acknowledgements to Gary Kramer and Ian Hoffman, here is a fascinating link to a creative use of isotopes!! http://www.facebook.com/l.php?u=http%3A%2F%2Fwww.nuclear.kth.se%2F&h=lAQGV8PUGAQEpz-SAWsItXUa-z29v_3p6G7mcupqJJ8eSjQ Hope this works! - =RPB