Final answer:
Pre-op checks for a GM counter include verifying battery voltage, conducting efficiency calibration, and measuring background radiation levels. These checks are important for accurate operation, with battery checks recommended daily, and calibration and background checks as specified or per use.
Step-by-step explanation:
The pre-op check of a GM counter (Geiger-Müller counter) includes several important steps to ensure that the instrument is functioning properly. These checks are critical for the accurate measurement of ionizing radiation levels. Firstly, the battery voltage should be checked to ensure that the unit has enough power for consistent operation. Secondly, efficiency calibration should be conducted to make certain that the counter correctly indicates the counts per unit of radiation.
This is often done using a known source of radiation and comparing the readings with expected values. Thirdly, measuring the background radiation level is crucial to account for the natural occurring radiation present in the environment during measurements. As for the frequency of these checks, while there isn't a one-size-fits-all answer, the commonly recommended practice is to perform a check on the battery voltage daily, ensure efficiency calibration is performed periodically as specified by the manufacturer or based on usage, and record the background radiation level at the start of each use or daily.