Investigations on imaging properties of inorganic scintillation screens under irradiation with high energetic heavy ions

This work represents the investigations in imagine properties of inorganic scintillation screens as diagnostic elements in heavy ion accelerator facilities, that were performed at GSI Helmholtz Centre for Heavy Ion Research (Darmstadt, Germany) and TU Darmstadt. The screen materials can be classified in groups of phosphor screens (P43 and P46 phosphor), single crystals (cerium-doped Y₃Al₅O₁₂) and polycrystalline aluminum oxides (pure and chromium-doped Al₂O₃). Out of these groups, a selection of seven screens were irradiated by five different projectiles (proton, nitrogen, nickel, xenon and uranium), that were extracted from SIS18 in fast (1 μs) and slow (300-400 ms) extraction mode at a specific energy of E_spec=300 MeV/u. The number of irradiating particles per pulse was varied between 10⁷ and 2.10¹⁰ ppp and the scintillation response was recorded by a complex optical system. The records served on the one hand for investigations in the two-dimensional response to the irradiating beam, namely the light output L, the light yield Y and the characteristics of the beam profiles in horizontal and vertical direction. On the other hand the wavelength spectrum of the scintillation was recorded for investigations in variations of the material structure. A data analysis was performed based on a dedicated Python script. Additionally three conventional methods (UV/Vis transmission spectroscopy, X-Ray diffraction, Raman fluorescence spectroscopy) were performed after the beam times for investigations in the material structure. Nevertheless, neither structural variations nor material defects, induced by the ion irradiation, were proven within the accuracy range of the used instrumentation and the given ion fluences. Besides the irradiation under varying beam intensity, radiation hardness tests with fast and slow extracted Nickel pulses at 2.10⁹ ppp and a specific energy around E_spec∼300 MeV/u were performed and the scintillation record was used to examine the material stability under long time application. Here, the light yield Y of the targets was nearly constant or decreased only in the range of 10-15 %, relative to the initial value. For the targets with single crystal characteristic (P46, YAG:Ce), Y even increased slightly and than saturated, offering an enhanced mobility of charge carriers under irradiation. The emission spectra were reproduced continuously and the beam profiles showed good accordance to the reference methods. Within all performed beam times, the targets offered a great stability. Non-linear characteristics, e.g. due to quenching during irradiation at high beam intensities, were not observed. The light yield Y showed a decreasing tendency as function of calculated electronic energy loss dE/dx. The characteristics of the calculated beam profiles, as well as the recorded emission spectra did not change significantly. So a material degradation in the investigated materials was not verified. This observation is confirmed by the performed material characterization measurements. The need of target replacement, e.g. due to damage, did not occur and was thus not performed during the complete investigations. As material for future beam diagnostics of FAIR cerium-doped Y₃Al₅O₁₂ single crystal with a thickness in the range of 300 μm is recommended in cross-points between different storage sections, due to the stable imaging properties for high energy ion beams, even under long-time irradiation. For beam alignment to experimental and research areas, common Al₂O₃:Cr is recommended due to the cost advantage.