High-Accuracy Ion Range Measurements using Fluorescent Nuclear Track Detectors

Novel fluorescent nuclear track detectors (FNTDs) are based on single aluminum oxide crystals doped with carbon and magnesium and laser scanning fluorescent microscopy. The detector crystals contain high concentrations of colour centres, consisting of two oxygen vacancies charge compensated by two magnesium ions. These colour centres exhibit radiochromic transformations under ionising radiation. Laser-induced fluorescence can then be stimulated with a red laser without photoionisation of the colour centres, thus allowing fast and non-destructive readout using commercial confocal laser scanning microscopes. Combination of excellent detection efficiency and full 3D spatial distribution information allows the measurement of individual particle trajectories through the detector volume. We irradiated FNTDs with protons (3, 6, 12 and 21 MeV/u) as well as with Fe, Kr and Xe ion beams (9.3 MeV/u). In contrary to standard procedure, we positioned the detectors’ c-axis perpendicular to the beam direction in order to measure both ranges and track lengths with resolutions between 100 nm and 400 nm. For protons, experimental results deviate less than 3% from caluclated data, for heavier ions less than 5%. On the poster, we also discuss the potential of range measurements using bulk instead of single track evaluations. Beside basic physic studies and irradiation control, this technique might lead to a new quality assurance for ion radiotherapy centres. Since aluminum oxide is a very inert, biocompatible material, implanted detectors or detectors in body cavities can help accessing direct information on a radiation treatment such as ion fluences, energies or ranges. Irradiations of FNTDs at the Heidelberg Ion-Beam Therapy Center within our study serve as a precursor of later in-vivo FNTD applications