Thermoluminescence dosimeter

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Thermoluminescence dosimeter

A thermoluminescence dosimeter (TLD) is a dosimeter that can be used to measure ionizing radiation .

In addition to age determination in archeology , thermoluminescence dosimetry is mainly used in radiation therapy , whereby it is also becoming increasingly important for radiation protection measurements. Properties such as the high radiation sensitivity, the relatively large measuring range and the high energy independence, the low fading and thus the very long storage capacity, as well as the small geometric dimensions, are used.

After a material capable of thermoluminescence has been exposed to ionizing radiation for a certain period of time, it emits electromagnetic waves in the range of visible light when it is supplied with thermal energy . The amount of light emitted is directly proportional to the energy absorbed. Since thermoluminescence dosimetry is a relative measurement method, a relatively complex calibration is necessary to achieve absolute values .

In principle, many materials are suitable for thermoluminescence processes, such as lithium fluoride , manganese-active calcium sulfate or calcium fluoride , natural fluorspar , lithium borate or beryllium oxide.

In 1950, lithium fluoride was proposed by Daniels in the USA for solid-state dosimetry. The most diverse areas of application for this generation of dosimeters were opened up, such as the dating of ceramics in art history, the exploration of the moon or the detection of possible volcanic activity.

The main position among the TLD materials is taken by lithium fluoride doped with magnesium and titanium . This is the result of many years of experience in determining the dose with this detector system and the high level of development that enables measurements with a high level of precision. A further improvement of the material could be achieved by other doping . A further increase in sensitivity could be observed in lithium fluoride doped with magnesium, copper and phosphorus . This material was first developed in powder form in the People's Republic of China in 1978 . In 1986 it was examined in solid form and only presented in Washington in 1992 at the 10th Congress of Solid-State Dosimetry.

By comparing the signal of different LiF TLDs, one of which has been enriched with lithium-6 (TLD-600) and the other has a reduced lithium-6 concentration (TLD-700), one can estimate the dose of thermal neutrons only captures Li-6 neutrons and then decays into tritium with alpha particle emission (n, α nuclear reaction). The alpha particles then ionize the detector along their particle track.

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