RaySafe 452 Survey Meter

Tube leakage is the radiation emitted from the machine outside the primary beam. All X-ray tubes have some radiation leakage. Tube leakage measurements are important for controlling the work environment for hospital staff who work close to the X-ray machine. Several measurements are made around the tube housing, and at positions where personnel typically stand during an operation. From tube leakage measurements, calculations are made to estimate an operator’s body radiation dose, for a single exposure or over an extended period.

According to IEC 60601-1-3, clause 12.4, the tube leakage is not allowed to exceed 1 mGy, averaged over the busiest hour in the lab, when measured at distance of 1 m from the focal point with a sensor area of 100 cm².

Wall leakage measurements are performed to ensure that radiation from X-ray rooms does not leak through the walls and exceed critical limits outside the X-ray room. Common measurement cases are at installations of new X-ray machines or after renovations of X-ray rooms.

The survey meter is scanned across the walls of interest while the X-ray machine is operating. Measurements are normally performed with a worst-case scenario of the settings on the X-ray machine (high kVp and/or high mAs). Typical points of interest for wall leakage measurements include the upper part of the wall, corners, windows, doors, etcetera. The survey meter is often hand-held but may also be mounted on a tripod for longer measurements. Low dose rates normally mean longer integration times of the survey meter.

From the survey meter measurements, calculations are made to check if critical radiation limits are exceeded. To perform the calculations correctly, it is vital to know if the location is a controlled or public access area. Furthermore, parameters such as workload, occupancy, leakage, and target dose need to be considered.

In nuclear medicine, radioactive substances are used for imaging and treatment of patients. Since radioactive substances have a specific decay time, and only are active for a certain amount of time, the drugs must be prepared at the hospital right before the examination. At preparation, it is important to ensure that no radioactive substances have been spilled on surfaces, or on the radiopharmacist preparing the drugs. The presence of unintended or undesirable radioactive substances is commonly referred to as contamination.

The survey meter is typically used to scan surfaces, as well as the gloves and hands of the radiopharmacist for spills. The survey meter is swept across the surface of interest to detect and measure the contamination. It is important to be close to the surface and to move the meter slowly, since the amount of spilled source can be very small and hard to detect.