Sensitivity changes of LiF:Mg,Ti and LiF:Mg,Cu,P TL detectors after proton exposures

Two most common types of LiF-based thermoluminescent (TL) detectors LiF:Mg,Ti (natural Li: MTS-N) and LiF:Mg,Cu,P (natural Li: MCP-N) have been studied for sensitivity loss after 60 MeV proton and gamma rays (⁶⁰Co) doses ranging between 0.5 and 30 Gy. The sensitivity (main peak area) of LiF:Mg,Ti was found to be reduced by almost 10% after the highest proton dose of 30 Gy with respect to the lowest dose of 0.5 Gy. The sensitivity loss was noticeable even after 5 Gy of protons. After gamma-ray exposures the sensitivity loss of LiF:Mg,Ti was smaller than after protons. LiF:Mg,Cu,P detectors show opposite effect: gamma-rays cause a stronger sensitivity loss than protons. The high-temperatures peaks of LiF:Mg,Ti decreased much more significantly than the main peak (by 40%). The decreased sensitivity may be partly (depending on the dose radiation type) recovered by application the extended annealing procedures: 400 °C/20 h for MTS-N and 10 min at 270 °C followed by 1 h at 240 °C for MCP-N. The observed changes of sensitivity are of importance for dosimetry in proton radiotherapy. - Highlights: • Sensitivity changes of TLDs were studied after proton and gamma doses up to 30 Gy. • Sensitivity loss of LiF:Mg,Ti and LiF:Mg,Cu,P is different for protons and γ-rays. • A prolonged annealing time partly restores the sensitivity