I just did some research on Cohen, he's my hero!
"When Ralph Nader described Plutonium as "the most toxic substance known to mankind", Cohen, then a tenured professor, offered to consume on camera as much Plutonium oxide as Nader could consume of caffeine, the stimulant found in coffee and other beverages, which in its pure form has an estimated LD50 of 13-19 grams for an adult human. Professor Cohen maintained that the radioactive substance would pass through his intestinal tract unabsorbed."
Interesting, twomers. Here's a web article http://www.nei.org/index.asp?catnum=3&catid=1295, it's wierd that there would be a shortage. People aren't scared of radioactivity are they?