Alpha particles, beta particles, and gamma-rays originate in nuclei and can be detected using a simple hand-held counter like the one shown in the photograph at the left below. The sources shown in the photograph are a 241Am alpha particle source (second from left in front), a 90Sr beta particle source (left front with yellow label), and a natural uranium source (primarily 238U) for gamma-rays. The uranium ore is encased in plastic.
If something is placed between the radioactive source and the detector, the particles might be stopped. The photograph also shows three possible "stoppers" of nuclear radiation: a lead brick, a thin sheet of lead, and a piece of paper (on the lead sheet).
The question this week is which "stopper" will work for each of the sources:
Click here for Answer #144 after March 24, 2003.
