Protection Against Radiation

By far the best shielding against radioactivity is Gauss' law: the intensity of a point source falls off as the square of its distance from the observer. All localized sources are labelled with their activity at a given distance, for instance ``10 mr/h at 1 m.'' If one keeps at least 10 m away from such a source, one will receive less than 0.1 mR per hour, which is not worrisome. Needless to say, one should never touch a radioactive source, because 1/r² can be very large as r goes to zero. Other safety measures include lead aprons, which are effective only for X-rays and -rays, and thick concrete shielding for neutrons and high-energy charged particles (these are much in evidence at TRIUMF).