Radiation measurements and approvals

Radiation is measured for a variety of reasons, and there are different types of radiation detectors in use. In all measurements, it is important to use a right kind of measuring instrument for the purpose and to ensure that the instrument is in working order and calibrated. The measurement result must also be interpreted correctly. Some radiation measurements require separate approval.

Radiation measurements are carried out to protect workers when monitoring exposure conditions or individual doses. Measurements are also needed for quality assurance of the use of radiation and in health care when determining the radiation exposure of patients. In addition, radon measurements are carried out to assess the exposure of both workers and the general public. In order for the measurement results to be reliable, radiation measurements must be made with a suitable, intact and calibrated radiation detector that is in full working order. In addition to radiation measurements, computational methods are also used to determine radiation exposure. For more detailed information on the requirements for radiation meters is available in the Radiation and Nuclear Safety Authority Regulation on Measurements of Ionizing Radiation STUK S/7/2021.

Selecting a suitable radiation meter

When selecting a radiation meter, ensure that it is capable of measuring the type of radiation and the dose rate in question and that the energy range of the meter is suitable. The characteristics of the radiation meter must be suitable for the application, and the prevailing environmental conditions must not influence the measurement result in unpredictable ways.

The suitability of the radiation meter has to be verified particularly carefully when measuring pulsed radiation, very high dose rates or low-energy radiation. Typically, a single radiation meter type is not suitable for measuring all types and qualities of radiation. For example, a dose rate meter cannot be used for determining surface activity caused by radioactive contamination.

Calibration and condition monitoring

Radiation meters must be properly calibrated. Calibration means determining a calibration factor for the radiation meter, i.e. the ratio between the value indicated by the radiation meter and the value of the measured quantity. Calibration also involves determining uncertainty for the calibration coefficient. Radiation meters are calibrated in a laboratory that has traceability to international radiation measurement standards. A radiation meter has to be calibrated before it is put into operation. Thereafter, the calibration will be carried out at least once in every five years, unless otherwise specified at the time of approval of the measurement method or operations.

Stricter requirements have been set for the calibration intervals of meters used in healthcare and radon measurements. The calibration interval of a field instrument used for measuring medical exposure may not exceed two years. The calibration interval of measuring instruments used for dose calibration of radiotherapy equipment used for external radiotherapy may not exceed three years, and the same calibration interval applies to the radiation sources and measuring instruments used for calibration of radiation sources in brachytherapy. The calibration interval of a meter and measurement system for airborne radon concentration and radon exposure may not exceed two years.

Calibration might need to be repeated more frequently if the meter is adjusted or problems are detected in its operation. Initial calibration by the manufacturer is often sufficient for commissioning a radiation meter.

During calibration, the meter reading is usually not adjusted. The true value of the quantity of radiation is obtained by multiplying the meter reading by the calibration factor. The calibration factor may depend on the radiation quality to be measured. Therefore, the calibration has to be performed for the energy range for which the meter will be used.

The operating condition of the meter must be checked regularly between the calibrations. This includes checking the general condition of the meter and a functional test using a suitable radiation source.

Accuracy of measurements in radiation and dosimetry

All measurements are subject to uncertainty. Their impact on the measurement result is assessed in a measurement uncertainty estimate. The measurement uncertainty estimate indicates how well the measurement result describes the actual value of the measured quantity and what factors affect the measurement uncertainty.

Approval of radon measurements

Radon measurements carried out to assess occupational or public exposure or to ensure safety require an approval from the Radiation and Nuclear Safety Authority. The prerequisite for approval is that the equipment used for measurements meets the requirements laid down in the Radiation Act and the decrees and regulations issued on the basis thereof, and that the equipment has been appropriately calibrated. The calibration of the equipment must be valid at the time of measurement.

Form: Approval of radon measurements (in Finnish)

The test report based on the measurement must be compliant with the standard. The calibration factor determined during calibration must be taken into account when reporting the results of radon measurements. The actual radon concentration in respiratory air is obtained by multiplying the result given by the radon measuring device by the calibration factor.

More information on measuring radon

Approved radon measurements

The Radiation and Nuclear Safety Authority (STUK) has granted several different operators an approval to carry out radon measurements. The approvals are in force for a limited period and must use the meter or measurement method for which the approval has been applied for.

Table 1. Alpha track radon detectors with a valid approval and calibration.

*) Distributor stated by the holder of the approval decision.

Table 2. Portable alpha track radon detectors with a valid approval and calibration, intended for measuring radon exposure.

*) Distributor stated by the holder of the approval decision.

Table 3. Continuously operating radon concentration measuring instruments with a valid approval and calibration.

Bulletin on radon measurements with Corentium Pro measuring instruments (in Finnish)

Approval of dosimetry services

Dosimetry service providers who provide measurement services for individual dosimetry of workers, must apply for approval from the Radiation and Nuclear Safety Authority. An approval has to be sought for the dosimetry service itself and for the measurement methods used for individual dose monitoring.

The application for approval must demonstrate that the requirements laid down in the Radiation Act and in the decrees and regulations issued on the basis thereof are met. This can be demonstrated, for example, by calibration certificates, test reports and measurement uncertainty estimates.

Table 4. Approved dosimetry services. 

Fees for radiation practices regulation