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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.¹⁷ Other safety measures include lead aprons, which are effective only for X-rays and $\gamma$-rays, and thick concrete shielding for neutrons and high-energy charged particles (these are much in evidence at TRIUMF).