Efficiency of luminescent detectors for the measurement of the proton dose of cosmic radiation in the Earth's orbit and in the dosimetry of proton beams

Project coordinator: Paweł Bilski, Assoc. Prof.

Lead time: 2011 – 2014

The aim of this research project is to determine the efficiency of relative luminescence detection (mainly thermoluminescent, TLD) of radiation detectors for protons and its dependence on proton energy.

Relative efficiency of luminescence (REL) is defined as the ratio of intensities of emitted luminescence light, per unit dose, for a given type of radiation, to the same dose of reference gamma radiation (Cs-137 or Co-60 gamma-rays). Relative efficiency depends on ionisation density.

For weakly ionizing radiation (gamma rays, X-rays, electrons) REL is typically constant, therefore it is assumed to be equal 1. For densely ionising radiation REL typically decreases with increasing Linear Energy Transfer (LET), to values ranging between 0.05 and 0.5 at LET values around several hundred keV/um in water, depending of the type of detector.

Contradictory experimental data on REL have been reported. In a number of publications, REL of some thermoluminescence (TL) detectors (including lithium fluoride doped with magnesium and titanium, LiF: Mg, Ti) after doses of light ions (H and He, of LET<5 keV/um, corresponding to protons of energy above 10 MeV He and heavier ions of energies above 50 MeV/n), has been reported to exceed one, even by up to 30%. On the other hand, at least as many published results show REL for protons to be equal to one, or lower. The proposed research project will attempt to resolve this issue by a systematic study of proton REL for several TL detectors and its dependence of proton energy or other factors that may affect this value.

The main result of this project will be achievement - for the first time - of a large systematic collection of reliable data on the REL of various luminescent detectors and on its dependence on proton energy and dose.

Collection of such data will allow us to better understand the trapping and recombination processes which govern the phenomena thermo-and opto-luminescence in materials irradiated by ions. We will use this knowledge to improve the accuracy of dose measurements in such important applications as space and clinical dosimetry of external proton fields.