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  • Personal dosimetry
  • Types of dosimeters
  • Handling dosimeters
  • Dosimetry measurement

     

    Personal dosimetry

    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:

      TLD OSL
    Measured quantities Hp(10), Hp(0,07), Hp(3), Hpn(10) Hp(10), Hp(0,07), Hp(3)
    Measurement range 0,01mSv-20Sv 0,05mSv-10Sv
    Uncertainty of measurement from 0,1mSv ±17,5% at value of 0,1mSv ±25% od 0,2mSv ±10%
    Range of measured energies from 15keV (RTG and gama) from 0,2 MeV (electrons) heat neutrons from 15keV (RTG and gama) from 0,2 MeV (electrons)
    Fading ‹5% per year (at 20°C) ‹5% per year
    Repeated use yes yes
    Possibility of a quick current evaluation yes yes