Principle Investigators are responsible for maintaining access to an appropriate portable survey instrument when working with moderate energy beta-particle or photon-emitting radionuclides. Portable survey instruments require calibration with sufficient accuracy to provide an estimation of the presence of localized surface contamination. Calibration refers to the determination and adjustment of instrument response in a particular radiation field of known intensity. The percent efficiency of detection for various isotopes is posted on the side of your meter. Survey meters are calibrated semi-annually by the Radiation Safety Division or outside calibration providers as warranted.