Lectures on Physics has been derived from Benjamin Crowell's Light and Matter series of free introductory textbooks on physics. See the editorial for more information....

The hot potato

A nuclear physicist with a demented sense of humor tosses you a cigar box, yelling "hot potato." The label on the box says "contains 1020 atoms of 17F, half-life of 66 s, produced today in our reactor at 1 p.m." It takes you two seconds to read the label, after which you toss it behind some lead bricks and run away. The time is 1:40 p.m. Will you die?

The time elapsed since the radioactive fluorine was produced in the reactor was 40 minutes, or 2400 s. The number of elapsed half-lives is therefore t/t1/2 = 36. The initial number of atoms was N(0) = 1020 . The number of decays per second is now about 107 s-1, so it produced about 2 107 high-energy electrons while you held it in your hands. Although twenty million electrons sounds like a lot, it is not really enough to be dangerous.

Last Update: 2009-06-21