Personal dosimetry is the set of methods and equipment used to measure and record the ionising radiation dose received by each individual worker. It is mandatory for all workers professionally exposed to ionising radiation under the ICRP system of radiological protection and national legislation transposing European Directive 2013/59/Euratom.
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This article presents the main types of personal dosimeters available, the applicable international standards, the dose limits established by the ICRP, and best practices for use in occupational settings.
What is Personal Dosimetry and Why is it Required
Personal dosimetry aims to ensure that occupational exposure to ionising radiation remains within legal limits and, ideally, as low as reasonably achievable (ALARA principle). Each worker classified as a Category A or B exposed worker must wear an individual dosimeter that records the accumulated dose over time.
The legal requirement derives from several normative instruments:
- Directive 2013/59/Euratom — EU directive establishing basic safety standards for protection against the dangers arising from exposure to ionising radiation; transposed into national law in all EU member states.
- ICRP Publication 103 — recommendations of the International Commission on Radiological Protection, adopted internationally; defines effective dose limits for workers and the general public.
- IEC 62387:2020 — international standard defining performance requirements for passive radiation dosimeters used in personal and environmental dosimetry.
Established Dose Limits (ICRP 103)
| Group | Effective Dose (whole body) | Eye Lens | Skin / Extremities |
|---|---|---|---|
| Exposed workers | 20 mSv/year (averaged over 5 consecutive years); max. 50 mSv in any single year | 20 mSv/year | 500 mSv/year |
| General public | 1 mSv/year | 15 mSv/year | 50 mSv/year |
| Apprentices (16–18 years) | 6 mSv/year | 15 mSv/year | 150 mSv/year |
Types of Personal Dosimeters
Several personal dosimetry technologies are available, each with specific characteristics regarding sensitivity, energy range, real-time reading capability, and cost. The choice of dosimeter depends on the work context, the types of radiation involved, and regulatory requirements.
1. Thermoluminescent Dosimeters (TLD)
Thermoluminescent dosimeters (TLDs) are the most widely used in individual dosimetry programmes in hospitals, radiology clinics, and nuclear facilities. They work on the principle of thermoluminescence: the detector material (typically lithium fluoride, LiF, or calcium fluoride, CaF₂) absorbs and stores energy from incident radiation in metastable electron states. When heated, these electrons return to equilibrium and emit light proportional to the dose received.
Key characteristics of TLDs:
- Excellent reproducibility and linearity for photons and X-rays
- Detection range: typically 0.01 mSv to 10 Sv
- Destructive reading (the signal is erased during readout)
- Reusable after reading and annealing
- Compliance with IEC 62387:2020
Interphysix distributes the Harshaw Model 3500 TLD Reader from Thermo Scientific — one of the world’s reference TLD readers, widely used in dosimetry laboratories, hospitals, and nuclear medicine departments.
2. Optically Stimulated Luminescence Dosimeters (OSL)
OSL dosimeters use carbon-doped aluminium oxide (Al₂O₃:C) as the detector material. Instead of heat, stimulation is performed using laser light or LEDs, which allows multiple readings without significant loss of the stored signal. This makes OSL dosimeters particularly suitable for partial readouts and dose audits.
Advantages of OSL over TLD:
- Non-destructive reading — the same dosimeter can be read multiple times
- Higher sensitivity to low doses (useful for very low-dose quality control)
- Permanent dose record — the material can be preserved for future audits
- Flat energy response for diagnostic X-rays
3. Electronic Personal Dosimeters (EPD)
Electronic personal dosimeters (EPDs) provide real-time dose readings and are frequently used as a complement to passive dosimeters (TLD or OSL). They are essential in controlled areas where there is a risk of exceeding dose limits, as they allow workers to monitor their exposure instantaneously and trigger configurable alarms.
Characteristics of EPDs:
- Real-time reading of Hp(10) (personal dose equivalent) and dose rate
- Programmable dose and dose rate alarms
- Internal memory and data interface (USB, Bluetooth, or infrared)
- Compliance with IEC 61526 (electronic individual dosimeters)
Interphysix offers EPD dosimeters from Thermo Scientific, including the RadEye G Series — high-sensitivity personal gamma dose rate meters — and the EPD TruDose by Mirion Technologies, designed specifically for precision radiological protection applications.
4. Film Badge Dosimeters
Film badge dosimeters were the standard in individual dosimetry for decades. They consist of a special photographic emulsion sensitive to ionising radiation. The dose is determined by optical analysis of the film’s darkening after development. Although less commonly used today, they are still maintained in some national dosimetry programmes due to their permanent record and the possibility of post-hoc analysis.
Limitations of film badge dosimeters:
- Sensitive to temperature, humidity, and light (risk of incorrect readings)
- Slow reading process (requires a processing laboratory)
- Limited linearity for very low or very high doses
- Largely replaced by TLD and OSL in modern programmes
Technology Comparison Summary
| Technology | Real-time reading | Reusable | Minimum sensitivity | Applicable standard |
|---|---|---|---|---|
| TLD | No | Yes | ~0.01 mSv | IEC 62387 |
| OSL | No | Partially | ~0.01 mSv | IEC 62387 |
| EPD | Yes | Yes | ~0.001 mSv | IEC 61526 |
| Film | No | No | ~0.1 mSv | ISO 1757 |
Applicable Standards and Regulations
IEC 62387:2020
This international standard specifies performance requirements for passive dosimeters used in individual and environmental dosimetry for photon radiation, electrons, and neutrons. It defines acceptance criteria for accuracy, resolution, energy response, and directional dependence. TLD and OSL dosimeters used in official dosimetry programmes must comply with this standard.
ICRP Publication 103 (2007)
The most recent recommendations of the International Commission on Radiological Protection (ICRP) establish the system of radiological protection based on the principles of justification, optimisation (ALARA), and dose limitation. Effective dose limits for workers are 20 mSv/year averaged over a period of 5 consecutive years, with a maximum of 50 mSv in any single year.
Directive 2013/59/Euratom
This EU directive establishes basic safety standards for protection against the dangers arising from exposure to ionising radiation. It defines employer obligations regarding individual monitoring, worker classification (Category A and B), dose records, and the role of the occupational physician and qualified expert in radiological protection.
Best Practices for Personal Dosimeter Use
Correct Positioning
- Whole-body dosimeter: wear at trunk level (preferably between the neck and waist), on the side facing the radiation source. In diagnostic radiology, typically at collar level on the lead apron.
- Extremity dosimeter (ring or wrist): wear on the dominant hand, with the detector facing the source.
- Eye lens dosimeter: wear at temple level or on specific glasses, indicated for professionals with high exposure to scattered X-radiation (e.g., cardiac intervention).
Periodic Exchange and Records
- Observe the exchange periodicity defined by the dosimetry service (monthly or quarterly, depending on exposure level and dosimeter type).
- Never use an expired or damaged dosimeter.
- Keep individual dose records for at least 30 years after the end of professional activity.
- Report to the radiation protection officer any anomaly or suspected accidental exposure.
Interphysix Solutions for Personal Dosimetry
Interphysix, as an authorised distributor of Thermo Scientific and Mirion Technologies, offers a complete portfolio for individual monitoring programmes:
- Harshaw Model 3500 TLD Reader (Thermo Scientific) — reference system for TLD dosimeter reading and processing.
- EPD TruDose (Mirion Technologies) — precision electronic dosimeter for radiological protection, with programmable alarms and dose memory.
- RadEye G Series (Thermo Scientific) — personal gamma dose rate meters, ideal for real-time monitoring in work environments.
For information on dosimetry programmes, calibration, and technical support, contact Interphysix.
Frequently Asked Questions about Personal Dosimetry
Who is required to use a personal dosimeter?
All workers classified as Category A exposed workers (exposure exceeding 6 mSv/year or equivalent doses exceeding 3/10 of extremity limits) and Category B (exposure between 1 mSv/year and Category A limits) are subject to individual monitoring. This includes radiographers, physicians and nurses in interventional radiology, nuclear medicine workers, radiotherapists, and nuclear industry workers.
What is the difference between TLD and OSL?
Both are passive dosimetry technologies that measure accumulated dose. The main difference is the reading method: TLDs are read by heating (thermoluminescence), making the reading destructive; OSLs are read by light stimulation (laser or LED) and can be re-read multiple times without erasing the signal. OSLs also offer higher sensitivity to very low doses and the possibility of preserving the record for future audits.
Does an electronic dosimeter (EPD) replace a passive dosimeter (TLD/OSL)?
EPDs are generally used as a complement to passive dosimeters. Regulatory frameworks consider the passive dosimeter read by an accredited laboratory as the official dose record. EPDs provide real-time information essential for operational control and alarms, but do not replace the legal dose record conducted by passive dosimetry in most regulatory contexts.
How often should I change my dosimeter?
Exchange frequency depends on the dosimeter type and estimated exposure level. For Category A workers, individual monitoring must be monthly. For Category B, it may be quarterly. The recommended maximum period for TLD and OSL is 3 months. High-exposure programmes (interventional radiology, nuclear medicine) typically use monthly exchange periods.
What should I do if I suspect an accidental high exposure?
If you suspect an unplanned or accidental exposure: (1) immediately notify the radiation protection officer; (2) do not remove or handle the dosimeter to avoid loss of evidence; (3) the dosimeter should be sent immediately for urgent reading to the dosimetry laboratory; (4) document the circumstances of the incident. Employers are legally required to investigate and record any accidental exposure exceeding 1 mSv.
Do dosimeters measure all types of radiation?
It depends on the dosimeter type and composition. Standard LiF TLDs are suitable for photons (X-rays and gamma) and electrons. For neutrons, specific materials are required (e.g., TLD-600 with ⁶Li or TLD-700 with ⁷Li in combination). Modern EPDs typically have separate detectors for photons and neutrons. It is essential to select the appropriate dosimeter for the type of radiation present in the workplace.
What is the ALARA principle in dosimetry?
ALARA (As Low As Reasonably Achievable) is the fundamental principle of radiological protection that recommends keeping radiation dose as low as reasonably achievable, taking into account economic and social factors. In practice, it involves optimising procedures, using adequate shielding, limiting exposure time, and increasing distance from the source. Personal dosimetry is the tool that verifies whether optimisation measures are effective and legal limits are respected.
Última actualização: 01/07/2026