Geiger- Müller survey meters (GM meters) are portable instruments used to detect and measure radiation. Facilities conducting work with radioactive materials detectable by GM meters need to have the meters calibrated at intervals not to exceed 12 months in accordance with 105 CMR 120.225.
Records of calibration should be maintained in the central safety files or other specific location according to institutional policy. Did you know that it is also a requirement to document GM meter operability checks at least quarterly?
GM meter operability checks are required to be performed each day that the meter is used. This involves placing the probe next to the check source and verifying that the reading is within 20% of the calibration reading. This should be one of the first steps that a radioactive material user takes when beginning to conduct work with an isotope that is detectable by a GM meter. Documentation of these operability checks must be recorded after instrument repair, battery change, instrument calibration, and at intervals not to exceed three months. If any check source reading varies by greater than 20% from the reading measured immediately after calibration, the meter should be taken out of service. The instrument would need to be repaired or recalibrated prior to being used for any compliance surveys.