Characterization of lithium fluoride fluorescent nuclear track detectors for linear energy transfer measurements in light-ion beams using confocal microscopy

Fluorescent nuclear track detectors (FNTDs) enable measurement of the linear energy transfer (LET) of heavy charged particles. Lithium fluoride (LiF) is widely used in solid-state dosimetry and has been shown to function as an FNTD, with all previous studies employing wide-field microscopy (WM). Compared with WM, confocal microscopy (CM) – while more complex and time-consuming – provides superior image quality, potentially allowing improved ion track visualization and detection. This study aims to establish the feasibility of imaging LiF crystals with CM to visualize ion tracks and measure LET. Single LiF crystals were irradiated with high-energy quasi-monoenergetic 4 He-, 12 C-, and 16 O-ions. Following irradiation, samples underwent thermal treatment to enhance fluorescence intensity and were subsequently imaged with a confocal microscope. Single-ion tracks were reconstructed from the resulting images, and fluorescence intensity was correlated with the LET in water (LET w ). The results demonstrate that it is feasible to image single ion tracks in LiF using CM. Detection efficiency reached nearly 100% for 16 O-ions at LET w = 50.4 keV μm -1 and for 12 C-ions at (31.8 and 10.6) keV μm -1 . Reduced efficiencies (∼50%) were observed for 16 O-ions at 18.9 keV μm -1 and for 12 C-ions at 17.9 keV μm -1 . For 4 He-ions, the efficiency was approximately 30%. The mean fluorescence track intensity increased with LET w , consistent with previous findings. CM shows potential for LET measurements using LiF-based FNTDs. However, at this stage, no significant improvement was observed for CM compared with WM.