TLD vs. OSL – Types of Dosimeters

Reviewed by Joel H. White, ME, Nuclear Engineering

Explore the basics of radiation, the differences between TLDs and OSLs, and the benefits of each type of dosimeter.

Thermoluminescent dosimeters (TLD) and optically stimulated luminescent dosimeters (OSL) are the two primary types of radiation dosimeters used in passive dosimetry.

Key Takeaways: TLD and OSL Dosimeters

• Professionals in occupational settings often prefer passive dosimeters for monitoring radiation over specific periods.
• Only badges approved for a legal dose of record from an NVLAP-accredited lab can fulfill the regulatory requirements from the United States Nuclear Regulatory Commission.
• Most occupational settings use thermoluminescent dosimeters (TLD) and optically stimulated luminescent (OSL) dosimeters to measure radiation exposure.
• Both personal radiation dosimeters measure radiation dose; TLDs require heat stimulation, while OSLs require only optical stimulation.

First: What is Ionizing Radiation? 

Ionizing radiation is a form of energy that causes the removal of electrons from atoms and molecules of materials (including living tissue, air, and water). This type of radiation can travel unseen and pass freely through these materials in the form of waves or particles. There are five types of ionizing radiation:

• Alpha particles
• Beta particles
• Neutron radiation
• Gamma radiation
• X-rays (electromagnetic radiation)

Ionizing radiation is powerful enough to affect the atoms in living cells, and higher doses can even damage genetic material.

Prioritizing the proper safety measures by using a radiation monitoring service to evaluate personal radiation exposure in occupational settings can help companies take action to prevent long-term health conditions like cancer and cardiovascular disease.¹

Active vs. Passive Dosimeters

There are two common types of personal radiation dosimeters: active and passive.

A passive dosimeter does not need an external source of energy or continuous monitoring to operate. Passive dosimeters are also known as integrating dosimeters, meaning they only provide the cumulative dose an individual is exposed to over a specific period of time. Badge wearers return passive dosimeters after the wear period (a week, month, quarter, or year) for analysis to meet required occupational radiation dose reporting.

Passive dosimeters differ from active dosimeters, which measure instant doses and provide accumulated dose over time. Not to be confused with personal emergency radiation detectors (or PERDs), active dosimeters provide a real-time direct display of information about radiation dose measurement for the individual wearing the device, but they do not provide a legal dose of record.²

Active and passive dosimeters can act as personal radiation detectors for employees working with radiation sources like radioactive material and radiation-emitting equipment. Also known as electronic dosimeters, an active dosimeter can be used with other emergency response applications to alert the wearer when they are approaching elevated or dangerous levels of exposure.

However, it’s important to note that active dosimeters do not provide a legal dose of record; you must use a badge approved for a legal dose of record from an NVLAP-accredited provider.

Passive dosimetry provides valuable data for assessing safety and potential health risks. Hospitals, dentist offices, veterinary clinics, and other occupational settings with low levels of radiation often prefer personal passive dosimeters because, unlike active dosimeters, they do not require continuous monitoring or an external power source.

NVLAP-accredited passive dosimeters can provide a legal dose of record to keep organizations in compliance with federal requirements.

Learn more about passive dosimetry in our blog post: Passive Dosimetry - What Is It, And Why Is It Important?

Radiation Regulatory Compliance 

The International Atomic Energy Agency (IAEA) provides safeguards to limit exposure to unnecessary and unintended radiation. These guidelines help ensure radiation dose limits align appropriately with medical needs, especially in situations involving X-ray exposure.

Occupational settings must also follow the United States Nuclear Regulatory Commission (NRC) and other state governing agencies in the United States. The NRC enforces radiation exposure regulations by setting industry standards for the safe use of nuclear materials and facilities to protect radiation workers. They impose these regulations through inspections, licensing, and enforcement actions against violators. State agencies typically oversee radiation devices in medical, veterinary, and industrial settings.

Both the IAEA and the NRC work to minimize exposure levels, establish robust regulatory frameworks, promote best practices, and provide technical support to ensure the safe use of nuclear materials and radiation.

Following radiation protocols helps protect public health and ensure radiation safety – for patients, employees, companies, and communities.

While many factors can contribute to an individual's personal dose equivalent, radiation dosimeters provide the dose for occupational radiation workers and act as an important first step toward radiation safety.

Using Dosimeters to Measure Radiation Dose

There are three types of dose in radiation dosimetry:

• Absorbed dose
• Effective dose
• Dose equivalent

Personal radiation dosimeters record the radiation absorbed by a person working in occupational settings with radiation or radioactive substances.

For clarification, radiation dose is measured in units of microSeiverts (mSv). Dose rate, on the other hand, is measured in terms of dose per unit of time, such as microSeiverts per hour.

Measuring Radiation Exposure: TLD or OSL

Both TLDs and OSLs measure radiation dose levels. However, OSL requires only light stimulation, while a TLD requires heat to stimulate the detector.

Radiation passing through a detector triggers optical and thermal stimulation, releasing electrons stored in the dosimeter. Luminescence (or visible light) is released when the electrons are released.

The material makeup of a TLD dosimeter and an OSL dosimeter is very similar. Both types utilize crystalline solids and capture point dose measurements, or radiation doses, in a relatively small volume.

To reiterate, the main difference between TLDs and OSL dosimeters is that TLDs require heat, while OSL dosimeters require only optical stimulation.

In the following sections, we'll go more into depth about the science behind TLD and OSL dosimeters.

How Thermoluminescent Dosimeters Work

First, radiation passing through a thermoluminescent dosimeter moves electrons into dosimetric traps. When the detector heats up (to a maximum of approximately 400º Celsius), the heat increase causes the trapped electrons to move and emit a light pulse, also known as luminescence. Only a small fraction of atoms (called the emission center or luminescence center) emit light.

Next, a photomultiplier tube (PMT) quantifies the visible light emitted. The emitted light is proportional to the amount of radiation exposure the dosimeter receives.

This process is how we measure exposure with a thermoluminescent dosimeter.

TLDs in Occupational Settings

Most occupational settings use TLD radiation dosimeter badges. TLDs are reliable passive radiation detection devices for workers in nuclear power plants, research laboratories, medical fields administering radiation therapy, veterinary clinics, and dental offices.

The most common types of thermoluminescent dosimeters include lithium fluoride, lithium borate, calcium sulfate, and calcium fluoride. Manufacturers will couple these compounds with one or more impurities to produce trap states for energetic electrons.

How Optically Stimulated Luminescent Dosimeters Work

Like TLDs, radiation passing through an OSL dosimeter moves electrons into dosimetric traps. The electrons stay in these traps until a detector uses light of a specific wavelength to stimulate the traps.

The increase in energy absorbed from the light causes the trapped electrons to move and emit a light pulse, also known as luminescence – in this case, optically stimulated luminescence.

OSL dosimeters typically use beryllium oxide because it is tissue equivalent, meaning it behaves similarly to human tissue when exposed to radiation. Beryllium oxide is also highly durable, sensitive, and resistant to environmental influences and fading.

However, some OSL dosimeters use aluminum oxide (Al2O3:C) instead of BeO. The choice between Al2O3:C and BeO dosimeters can depend on sensitivity requirements, energy dependence, readout method, and cost considerations.

Benefits of OSLs: Lower Limit of Detection

OSL dosimeters are generally more sensitive than TLD dosimeters, with a lower limit of detection (LLD). The lower limit of detection is the smallest amount of radiation that a dosimeter or detection system can reliably identify and measure.

A lower limit of detection in an OSL dosimeter is beneficial because it allows for the accurate measurement of even very low levels of exposure; OSLs can detect and quantify radiation doses below the threshold of other dosimetry methods.

A lower limit of detection is especially important in environments where minimizing radiation exposure is critical, such as in medical settings, nuclear facilities, and occupational radiation monitoring.

Both TLD and OSL dosimeters are capable of reporting very consistent and accurate Minimum Reportable Doses, as indicated on your Occupational Dose Reports.

Radiation Dosimeter Comparisons

Need more clarity on the differences between whole body dosimeters? We're sharing more information to give you more clarity.

All of RDC’s personal radiation dosimeters are NVLAP-accredited (Lab Code 100512-0), detect photons, and meet the legal dose of record requirements. RDC badge subscriptions include our industry-leading customer service and a MyRadCare account.

OSL Dosimeter Badges

RDC’s OSL is a two-element beryllium oxide (BeO) badge. OSLs work best for veterinarians, dentists, chiropractors, and anyone at risk of occupational X-ray and gamma exposure.

View OSL Dosimeter Badge details and specifications.

Thermoluminescent Dosimeter (TLD) Badge

The TLD from RDC is a four-element thermoluminescent dosimeter badge. TLDs work best for medical practitioners, healthcare workers, veterinarians, dentists, and workers in nuclear power facilities.

View TLD Badge details and specifications.

TLD + Neutron

RDC’s TLD + Neutron badge is a four-element thermoluminescent dosimeter badge. TLD + Neutron badges work best for medical, industrial, research professionals, and technologists.

View TLD + Neutron Dosimeter details and specifications.

NetDose™ Dosimeter

NetDose™ Dosimeter is a semi-passive digital dosimeter that offers real-time dose determination using silicon photomultiplier (SiPM) technology.

This digital dosimeter works best for individuals working in environments with gamma rays or X-rays, or in high dose situations, such as fluoroscopy.

View NetDose™ Dosimeter details and specifications.

Find Your Best Fit for Radiation Monitoring

Radiation Detection Company has provided quality personal dosimetry service to over 31,000 organizations for over 75 years. We offer various radiation detection services, including:

• TLD Whole Body Radiation Monitoring
• OSL Whole Body Radiation Monitoring
• TLD Ring Dosimeter
• OSL Wrist Badges
• Fetal Radiation Monitoring
• Area TLD Solutions
• Leak Tests
• Netdose™ Dosimeter – a digital dosimeter

Finding the best fit for personal radiation monitoring service goes beyond matching your badge to your equipment. At RDC, we want you to feel confident and empowered with the information you need to protect yourself, your staff, and your community.

In the section below, we'll explain how to sign up for personal radiation detection service with RDC.

Confirm Your Type of Radiation Badge

Before ordering personal dosimeters, consider the radiation type, range, and equipment used. Locate the label on your radiation-emitting device to determine what kind of radiation is being emitted to ensure you're covered.

Whole body badges monitor occupational exposure to a single individual to ensure the dose remains within the allowable occupational dose limits.

Depending on your industry's requirements and staff needs, you may also need to consider other dosimeters, such as extremity badges, fetal radiation badges, and area monitors.

Select Your Number of Badges

We recommend ordering badges for any employee working with or around chronic radiation exposure. Federal requirements require individual personnel monitoring if the dose received for any given category is likely to exceed 10% of the dose limit in one year.

As a reminder, RDC automatically includes a control badge in every order to account for any anomalies during transit. We recommend including at least one spare badge on your roster to account for turnover and avoid mid-cycle shipments.

Choose Your Radiation Reporting Frequency

How often you exchange your badges will determine how frequently you receive a dose report. The recommendations below act as a general guide, but for more specific requirements, refer to your Radioactive Materials License.

RDC offers monthly, bi-monthly, quarterly, semi-annual, and annual reporting based on your needs. Quarterly reporting frequency is the most common for all badge types (except fetal) unless the state requires more frequent monitoring.

Remember to return your badges at the end of each exchange period to get your dose report! Pregnant employees should exchange fetal badges monthly to receive timely dose reports as required by the NRC.

Want to send this badge order guide to yourself as a reminder? Enter your information here and pick up where you left off.

Frequently Asked Questions

What are the advantages of OSLD over TLD?

OSLDs (also known as OSLs) offer faster readout, reusability, and greater sensitivity. They are typically smaller, require no heating, and are less affected by environmental factors than TLDs.

However, TLDs have other advantages like long-term stability, consistent response to different types of radiation, lower cost, easier readout, and less sensitivity to light and environmental factors compared to OSLDs.

Will you have as accurate of a reading with TLD as you would an OSL dosimeter?

Yes. Both personal radiation dosimeters provide accuracy of dose determination with proper calibration and handling.

The “right” dosimeter is the one that provides solutions for your needs and industry demands. For example, a vet clinic that does not have beta emitters would choose a simpler OSL dosimeter.

What is a OSL dosimeter?

An OSL dosimeter measures exposure to radiation by using a material that stores energy when exposed to radiation.

Radiation monitoring providers then capture and quantify the stored energy using light to provide an accurate determination of dose for a specific wear period, which is later captured on dose reports.

What does TLD mean in radiology?

TLD stands for thermoluminescent dosimeter. TLDs are personal radiation detectors that use thermal stimulation to measure the amount of radiation dose received during a wear period.

Reference

1. “Radiation Health Effects.” United States Environmental Protection Agency, 4 Feb. 2024, www.epa.gov/radiation/radiation-health-effects.
2. “Determination of Radiation Exposure from Dosimeters.” NRC Web, United States Nuclear Regulatory Commission, 17 Oct. 2017, www.nrc.gov/about-nrc/radiation/protects-you/hppos/hppos186.html.

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