The following is a systematic description of the calibration method for personal radiation dose meters, covering calibration principles, processes, standard basis, and quality control points:
1、 Calibration Fundamentals and Core Standards
The calibration of personal dosimeters (such as TLD and electronic dosimeters) must follow strict standardization procedures to ensure that measurement results can be traced back to national standards. The current core standard in China is GB/T 12162.3-2024 (replacing the 2004 version), which is equivalent to the international standard ISO 4037-3:2019 and specifies the following key contents:
1. Scope of application: Covering dose meters and personal dosimeters in X/gamma ray fields, applicable to photon energy range of 8 keV~9 MeV.
2. Calibration objective: Determine the energy response and angular response characteristics of the instrument, and provide the conversion coefficient from the specific release energy of air ($K0 $) to the actual amount (such as $H '(0.07) $, $H_p (10) $).
3. Reference radiation field: Two types of reference radiation fields, matching or characteristic, need to be established to clarify the calibration procedures under 1m and 2.5m irradiation conditions.
>Note: Calibration essentially establishes the correlation between the readings of the dosimeter and the standard value through relative measurement, and its reliability depends on precise control of the reference radiation.
2、 The entire process of calibration implementation
1. Pre preparation stage
-Equipment status confirmation:
-Check the integrity of the appearance of the dosimeter (no damage to the sensor, sealing of the housing);
-Verify that the battery level and data storage function are normal;
-Preheat the instrument to a stable working state (electronic dosimeters usually take more than 30 minutes).
-Standard source and phantom configuration:
-Select standard radioactive sources verified by the National Institute of Metrology;
-Select the phantom based on the monitoring object: ICRU board phantom for whole-body monitoring, cylindrical phantom for intraocular lens dose monitoring.
2. Establishment of reference radiation field
According to the requirements of GB/T 12162.3-2024, the following must be met:
-Uniformity of radiation quality: coefficient of variation of dose rate within the irradiation field is ≤± 5%;
-Charged particle equilibrium condition: When the energy is higher than 65 keV, it is necessary to ensure that electronic equilibrium is achieved at the reference depth (such as 0.07mm, 3mm, 10mm).
3、 Key quality control links
1. Traceability chain guarantee:
Calibration must be carried out through a secondary standard laboratory (SSDL) or directly sent to a national metrology institute (such as the National Institute of Metrology, NIM) to ensure that the values are traced back to the original standard (such as a water calorimeter or graphite calorimeter).
2. Periodic resumption of school:
-The regular resumption period is ≤ 1 year;
-Immediate recalibration is required in the event of severe collision, immersion, or abnormal readings.
3. Application consistency verification:
In practical workplaces, the dual dosimeter method (synchronous monitoring of the inside and outside of the torso) is used to verify the effectiveness of calibration, especially for uneven radiation fields such as interventional radiology.
V. Conclusion
Calibration of personal dosimeters is the cornerstone of radiation protection systems, which requires the integration of precision metrology technology, standard specifications, and practical experience. With the implementation of GB/T 12162.3-2024, China has further improved its technical framework in areas such as energy response optimization and intraocular lens dose assessment. Users should strengthen their awareness of full lifecycle management, forming a closed loop from selection and procurement, periodic calibration to daily quality control, and effectively safeguarding the health rights and interests of radiation workers.