Dosimeter
Dosimeters are measuring devices for measuring the radiation dose - as absorbed dose or equivalent dose - in the context of radiation protection . In contrast to the dose rate meter , the instantaneous dose performance , so the radiation dose measured per time period, a dosimeter sums the dose rate over time to time.
In Austria , after the definition of the term in the calibration regulations, the designation can also be used for a dose rate meter.
Dosimeters are mostly intended to be worn on the body, possibly on parts of the body that are particularly exposed to radiation (finger ring dosimeters) and are then called personal dosimeters .
Personal dosimeter
- Fountain pen dosimeters (named after the shape and size of the housing): The electrical charge and thus the voltage of a capacitor is reduced by incident ionizing radiation . The dose received since charging can be read at any time from the position of a metal thread above a scale in the device. The display can be cleared by recharging, i.e. H. reset to zero. Fountain pen dosimeters register X-rays and gamma radiation as well as (with some restrictions, depending on the beta radiation permeability of the material) also beta radiation (see also Sievert chamber ).
- Film dosimeter : A in a plaque with various filter fields (for spreading the sensitivity range and differentiation between soft and hard radiation) befindlicher film is blackened by the irradiation. After development, the absorbed dose can be measured by comparing the density with defined irradiated films.
- Thermoluminescence Dosimeter (TLD): In suitable crystals , the X-ray or gamma radiation generates microscopic changes which, when evaluated (by heating the crystal), emit the absorbed radiation energy in the form of visible light. The dose results from the light output.
- Digital dosimeters use electronic sensors and digital signal processing and show the current radiation dose received on a digital display, usually in µSv . Some devices can be set in such a way that they emit a warning tone as an alarm signal when certain radiation doses are reached ( alarm dosimeters or dose warning devices ).
- The measuring method of nuclear track etching can also be used. In this, the ion traces in materials such as mica or polymers are evaluated .
Readability
Another distinction, which also determines the type of use, is readability.
- Devices that can be read directly are electronic devices that show the dose that has been taken since the device was switched on on a display. They are sometimes combined with dose rate measuring devices, as the technical structure is very similar.
- Dosimeters that cannot be read directly can only be read out retrospectively using special equipment.
use
The dosimeters (film dosimeters, TLD etc.) that cannot be read immediately and cannot be erased are used as officially approved dosimeters for routine monitoring of occupationally exposed persons and are usually evaluated monthly.
Electronic dosimeters often have devices to protect them from being switched off accidentally. This can consist, for example, of an additionally required pin on the switch-off switch, or the switch-off switch can only be pressed in a certain sequence. They are mostly used in radiation protection units , such as the military or fire brigade , and in uncontrolled radiation areas. Therefore, they are often referred to as tactical dosimeters .
For emergency teams such as the fire brigade, in addition to the officially approved dosimeters, the dose warning devices described above (also known as dose warning devices) are worn. In Germany, for example, this is regulated by the fire brigade service regulation (FwDV) 500 “Units in NBC operations ”. Since the official dosimeters can only be read out after use, there would otherwise be no warning of an excessively high dose in use. The dose guide values according to FwDV 500 are 15 mSv for deployments to protect property, 100 mSv to ward off dangers to people and to prevent a significant spread of damage and 250 mSv to save human lives. These guide values are preset in the dose warning devices and are then selected for the respective application scenario. When the reference value is reached, the device alerts the emergency services. The dose warning device should not be confused with the dose rate warning device also used in radiation protection .
Depending on the use, dosimeters are worn differently. Non-readable items can be worn under any protective clothing. They should record the dose that comes as close as possible to that of the body itself. On the other hand, readable dosimeters must be worn ready to hand over any protective clothing. Personal dosimeters that are also supposed to detect alpha radiation, for example in facilities for water extraction ( Section 95 Radiation Protection Ordinance ), must be worn on clothing due to the low penetration depth of the alpha particles.
Detectors for dosimetry in quality assurance in radiation therapy
In addition to personal dosimeters, other types of detectors are also used for dosimetry , ie dose measurement. Some are waterproof, i.e. suitable for measurements of the depth dose curve in a water phantom , the others are only suitable in connection with a phantom made of plastic.
To determine the dose, a large number of correction factors and calibrations have to be taken into account during the measurement, including with regard to air pressure, temperature, dose rate, density of water, type of radiation, radiation energy, recombination, polarity, humidity, detector geometry, operating voltage. Detailed measurement reports can be found in DIN 6800-2 and in a publication by the International Atomic Energy Organization .
See also
- Matryoshka (radiation measurement)
- Radiation exposure
- Radiation resistance
- Radiation damage
- History of radiation protection
Web links
- The " Radiation Protection Glossary " from Forschungszentrum Jülich with numerous explanations of terms and definitions for radiation, radiation measurement and dosimetry
- Glossary of personal dosimetry terms from the Materials Testing Office in North Rhine-Westphalia
Individual evidence
- ↑ Federal Office for Metrology and Surveying (BEV): Ordinance of the Federal Office for Metrology and Surveying on calibration regulations for dosimeters used in X-ray diagnostics § 2. (1) A "dosimeter" is a dose measuring device and / or dose rate measuring device. from 2013, accessed on February 10, 2020.
- ↑ FwDV 500 - units in ABC use. Federal Office for Civil Protection and Disaster Assistance, January 2012, accessed on February 27, 2020 .
- ↑ Absorbed Dose Determination in External Beam Radiotherapy: An International Code of Practice for Dosimetry based on Standards of Absorbed Dose to Water Technical Report Series 398, IAEA, Vienna 2000, ISSN 1011-4289 . Retrieved March 2, 2015
