The personal monitoring is the repeated measurement of quantities important with regard to the irradiation protection, enabling control, checking, monitoring and evaluation of the irradiation extent to which the persons working with sources of ionising radiation are exposed. The personal monitoring includes the measurement itself, evaluation and interpretation of results. It is intended to prevent an excessive level of irradiation. The detectors for measuring doses of irradiation are called dosimeters.
Generally, 3 methods of the integral personal dosimetry are used:
The film dosimeters belong to the oldest types of integral dosimeters for X rays, gamma, beta and heat neutrons measurements. Their functioning is based on the ionizing radiation capability to cause the blackening of the sensitive photographic layer. By developing film using a chemical process, we get a latent image, where the level of darkness is proportional to the radiation dose.
Thermoluminescence method is based on the feature of some crystals (e.g. LiF, CaF2, CaSO4, and some others), the atoms of which excite under radiation. This energy disrupts the equilibrium status of the orbital electrons that are caught in so called traps. Only after receiving an additional energy (in our case by heating the crystal to the specified temperature), the electrons return to their equilibrium status by emitting photons. The amount of emitted photons is proportional to the radiation dose.
Advantages of TL detectors and thermoluminescence method:
Optically stimulated luminescence functions on the similar principle as TL, but the basic difference lies is the evaluation. Instead of heating, the crystal (e.g. Al2O3) is lightened by the LED diode green light; the result is the emission of blue light of intensity corresponding to the rate of ionising radiation.
For determination of the whole body personal doses and of equivalent doses in hands, in Slovak legal metrology, n.o. the TL dosimeters are used.
Comparison of basic characteristics of TL and OSL dosimeters:
Personal dosimetry workplace of SLM uses the thermoluminescence dosimeters (hereinafter referred to as TL dosimeters) for performance of its dosimetry services.
Every TL dosimeter is a special and unique integral detector, integrating “information on dose” permanently, without possibility to be “switched off” when the person is not exposed to the source of ionizing radiation, because during this time the dosimeter records the doses of ionizing radiation from the natural environment.
The life of TL dosimeter is more than 500 evaluation cycles, i.e. cca 80 years provided, it is handled with care.
The TL dosimeter consists of several parts:
Personal dosimetry workplace assesses and hires the following types of TL dosimeters:
intended for 1 month exposures (BG2/M) consists of a holder TLD type 8814 and double-element card type LBG 0110
intended for 3 months exposures (BG2/K) consists of a holder TLD type 8814 and double-element card type LBG 0110
intended for 1 month exposures (BG4) consists of a holder TLD type 8805 and four-element card type LBG 1111
intended for 1 month exposures (NBG) consists of a holder TLD type 8805 and four-element card type BGN 7776
consists of holder - ring and TLD chip (disk with one TL element type TLD 100) and evaluation application card for chips evaluations
consists of holder - wristband and TLD chip (disk with one TL element type TLD 100) and evaluation application card for chips evaluations