Dosimeter Definition
A radiation dosimeter is a device, instrument, or system that calculates or evaluates dosage, kerma, absorbed dose, or equivalent dose, or their time derivatives (rates), or related amounts of ionising radiation, either directly or indirectly. A dosimeter device is a combination of a dosimeter and a reader. The method of determining the value of a dosimetric quantity experimentally using dosimetry systems is known as measurement. The value of a dosimetric quantity expressed as the combination of a numerical value and an acceptable unit is the consequence of a calculation.
In this article we will get to know about what is a dosimeter, uses and various applications. We will also know about home dosimeter.
What is a Dosimeter?
A dosimeter instrument is a device that measures the amount of ionising radiation a person has been exposed to. Dosimeters usually report a dose, which is the absorbed radiation energy in greys (Gy) or equal dose in sieverts (Sv). A personal dosimeter is a dosimeter that the person being monitored wears on the surface of their body and records the radiation dose received.
The dosimeter must have at least one physical property that is a function of the measured dosimetric quantity and that can be used for radiation dosimetry with proper calibration in order to function as a radiation dosimeter. Radiation dosimeters must possess many desirable characteristics in order to be useful. For example it is used in radiotherapy, precise knowledge of the absorbed dose to water at a given point and its spatial distribution, as well as the ability to calculate the dose to a patient's organ of interest, are critical. Accuracy and precision, linearity, dose or dose rate dependence, energy response, directional dependence, and spatial resolution are all desirable dosimeter properties.
There are Two Kinds of Dosimeters:
Passive Dosimeters - The Thermo Luminescent Dosimeter (TLD) and the film badge are two widely used passive dosimeters. A radiation-induced signal is produced by a passive dosimeter and stored in the unit. The data of the dosimeter is then processed and analysed.
Active Dosimeters - It is used to calculate the value of our exposure in real time. Instead of a passive dosimeter, an active dosimeter, such as an electronic personal dosimeter, could be used (EPD). An active dosimeter generates a radiation-induced signal and provides a real-time reading of the dose or dose rate observed.
Types of Dosimeters
There are many types of radiation dosimeters and each type has its own limitations.
Below We have Discussed Dosimeter Uses:
Film Badge Dosimeters
Ionizing radiation film badges are lightweight, portable devices that measure the cumulative exposure of ionising radiation. The process is identical to that of X-ray images. There are two sections to the badge: photographic film and a holder. The movie is hidden inside a badge. The critical material is a piece of photographic film that must be extracted and developed on a monthly basis. The film darkens when it is exposed to more radiation. The film's blackening is proportional to the dose, and doses up to 10 Gy can be calculated.
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TLD – Thermoluminescent Dosimeter
TLD stands for thermoluminescent dosimeter, and it is a passive radiation dosimeter that measures the intensity of visible light emitted from a sensitive crystal in the detector when it is heated to monitor ionising radiation exposure. A TLD reader measures the intensity of light released, which is affected by radiation exposure. Professor Farrington Daniels of the University of Wisconsin-Madison invented thermoluminescent dosimeters in 1954. TLD dosimeters may be used in circumstances where real-time data isn't needed, but accurate accumulated dose tracking records are required for comparison to field measurements or to determine the risk of long-term health effects.
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EPD – Electronic Personal Dosimeter
A modern dosimeter that can provide a continuous readout of cumulative dose and current dose rate, as well as warn the user if a given dose rate or cumulative dose is exceeded, is known as an electronic personal dosimeter. EPDs are particularly useful in high-dose areas where the wearer's residence period is restricted due to dose restrictions.
The EPD (electronic personal dosimeter) will show a direct reading of the dose or dose rate detected in real time. Electronic dosimeters can serve as both a supplemental and primary dosimeter. Electronic personal dosimeters and passive dosimeters are often used in conjunction to complement each other.
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MOSFET Dosimeter
A MOSFET dosimeter is a small portable system that can be used to measure and read radiation dose rates directly. The theory of operation is close to that of semiconductor detectors since it is based on the MOSFET transistor, the metal-oxide-semiconductor field-effect transistor (MOSFET). Medical dosimeters for radiotherapy radiation beams are now MOSFET dosimeters. Their physical size, which is less than 4 mm2, is their key benefit. MOSFET dosimeters sometimes replace TLD dosimeters in radiation therapy dosimetry because they have an instant readout.
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Self-Reading Dosimeter
Self-reading dosimeters are field-readable instruments that monitor cumulative dose and are worn on the body. These are machines that do not have a battery and are thus unpowered. This category includes the following devices:
Dosimeter made of quartz fibre. A quartz fibre dosimeter, also known as a self-indicating pocket dosimeter (SIPD), is a pen-like instrument that monitors the total dose of ionising radiation obtained during a single work cycle.
Photochemical cards that self-develop. A self-developing photochemical card is a credit card-sized emergency dosimeter that develops colour instantly. It's made to keep track of radiation exposure during a radiological event so that medical attention can be prioritised and worry and fear can be avoided.
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DIS Dosimeter
The DIS (also known as direct-ion storage dosimeter) is an electronic dosimeter which is used for dose information for both Hp(10) and Hp(0.07). It can be accessed instantly at work using an electronic reader device. The DIS dosimeter is made up of a non-volatile electronic charge storage element and an ion chamber. A thin, gas-filled ionisation chamber houses an analogue memory cell in a DIS dosimeter. Ionizations in the chamber wall and gas are caused by incident radiation, and the charge is retained for later readout. The DIS dosimeter is connected to an electronic reader device and read at the user's location.
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How Does a Dosimeter Work?
Dosimeters were originally badges made of film. The radiation exposure would leave a mark on the film, and the badges would be gathered and processed to determine the amount of radiation obtained.
Technology has now made the process much simpler. Digital badges, such as the Instadose+ dosimeter, will detect and record exposure, and the results can be downloaded to a computer, tablet, or mobile device almost instantly. Instead of having to gather and redistribute badges, the small badges can be conveniently clipped on clothing and remain with individuals. In terms of radiation measurement and control, it's a better option.
FAQs on Dosimeter
1. What is the main purpose of a dosimeter?
A dosimeter is a device used to measure an individual's total exposure to ionising radiation over a specific period. It does not provide any protection from radiation but acts as a personal monitoring tool to ensure that exposure levels remain within safe limits.
2. What is the difference between a dosimeter and a Geiger counter?
The key difference is their function. A Geiger counter is used to detect the real-time presence and intensity of radiation in a specific area. In contrast, a dosimeter measures the total, cumulative dose of radiation received by the person wearing it over weeks or months. A Geiger counter is for surveying an environment, while a dosimeter is for personal safety monitoring.
3. Who typically needs to wear a dosimeter and why?
Dosimeters are essential for any professional who works with or near sources of radiation. This includes radiographers and oncologists in hospitals, workers in nuclear power plants, and researchers in scientific labs. They wear them to track their cumulative radiation dose, ensuring it stays below legally mandated safety limits to protect their long-term health.
4. What are some common types of radiation dosimeters?
There are several types of dosimeters that work on different principles. Three common examples are:
- Thermoluminescent Dosimeters (TLDs): These use crystals that store energy from radiation and release it as light when heated, which can then be measured.
- Film Badge Dosimeters: These contain a piece of photographic film that darkens in proportion to the amount of radiation it is exposed to.
- Electronic Personal Dosimeters (EPDs): These are battery-powered devices that give an instant, digital reading of the radiation dose and can set off an alarm if a certain level is reached.
5. In what units is the radiation dose from a dosimeter measured?
The radiation dose measured by a dosimeter is typically reported in units of Sieverts (Sv) or, more commonly, millisieverts (mSv), which is one-thousandth of a Sievert. The Sievert is the standard unit that accounts for the biological effect of different kinds of radiation on the human body.
6. Does wearing a dosimeter protect you from radiation?
No, this is a very common misconception. A dosimeter is a passive recording device and offers no physical protection whatsoever. Its only job is to measure and record radiation exposure. Protection is achieved through other safety measures like lead shielding, increasing distance from the source, and limiting the time of exposure.
7. Why is it important to measure the cumulative dose over time, not just immediate radiation levels?
It's crucial to measure the cumulative dose because the biological harm from radiation is additive. Small exposures repeated over many months or years can add up to a significant total dose, increasing long-term health risks. Monitoring the cumulative dose ensures a worker's total exposure over their career remains safely below established limits.
8. What kind of radiation can a standard dosimeter badge detect?
Most standard dosimeter badges are designed to accurately measure high-energy radiation like gamma rays, X-rays, and energetic beta particles. They are generally not effective at detecting low-energy beta radiation (from isotopes like Tritium or Carbon-14) or alpha particles, which require more specialised detection equipment.
