ALARA - As Low As Reasonably Achievalbe

ALARA is an acronym for As Low As Reasonably Achievable. ALARA is a radiation safety principle for reducing radiation doses and releases of radioactive materials by using all reasonable methods. ALARA is a regulatory obligation for all radiation safety programs.

The three main principles of ALARA are time, distance, and shielding.

Minimizing time of radiation exposure minimizes dose.
Doubling the distance between your body and the radiation source will divide the radiation exposure by a factor of 4.
Using shielding materials such as Plexiglas for beta particles and lead for X-rays and gamma rays is an effective way to reduce radiation exposures.

time-distance-shielding
For more information, see the U.S. NRC's Minimize Your Exposure.