Calibration of the LiF - thermoluminescent detectors used for personal dose equivalent Hp(3) assessment

The issue of exposure of eye lenses of employees exposed to ionizing radiation is an interesting topic not only from the point of view of deterministic effects related to the occurrence of cataracts, but also dosimetric aspects, in particular the calibration of detectors in units enabling the assessment of eye lens exposure or personal dose equivalent Hp(3). The paper presents the idea of calibrating thermoluminescent detectors designed for the Hp(3) values measurement of gamma radiation, which the source is the process of annihilation of positrons emitted by the deoxyglucose marker - ¹⁸F radionuclide.

The method was based on the value of air kerma Ka to Hp(3) conversion coefficients (Hp(3,0°)/Ka) developed as part of the ORAMED project. High-sensitivity thermoluminescent detectors (MCP-N) produced in Poland were used in the measurements. During the exposure of the detectors, a ¹³⁷Cs gamma radiation source (irradiator ¹³⁷Cs/⁶⁰Co) and a 20cm diameter cylinder filled with water were used.

The value of conversion coefficient Hp(3,0°)/Ka for energy 511 keV is 1.31Sv/Gy and the calibration factor is (3.46±0.03)·10^-4 mSv/N (N - number of counts). Verification of the value of the obtained coefficient carried out using a cylinder with a diameter of 20cm showed a difference of less than 2% in relation to the value obtained by the method described in this paper.