Scintillation Screen Investigations for High-Current Ion Beams

At GSI, the Helmholtz Centre for Ion Research, the properties of scintillation screens, irradiated by an ion beam, were studied. For various materials, the different ion beams H⁺, C²⁺, Ar¹⁰⁺, Ni⁹⁺, Ta²⁴⁺, and U²⁸⁺ in the energy range from 4.8-11.4 MeV/u were applied with currents ranging from nA to some mA, delivered by the heavy ion LINAC at GSI. Scintillation screens are widely used for qualitative ion beam profile monitoring. However, precise measurements of the beam profile yield ambivalent results, especially for high beam currents. Thus, the properties (light yield, beam width, and higher statistical moments) of well-known scintillators, ceramic materials, and different quartz glasses are compared. The image of each ion beam pulse was recorded by a digital CCD camera and individually evaluated. A change of the imaged ion beam shape was observed for some materials. The recorded beam profile shows dependence on the scintillator material. Even for low beam intensities (17 nA) a difference in the beam width of about 25% was measured. Additionally, the light yield and beam width depend significantly on the screen temperature, which is increased by the ion impact. For ZrO₂ : Al the influence of the screen temperature on the statistical moments was investigated. Furthermore the spectra of scintillation screens were studied in the region from 350 to 750 nm for the irradiation with H⁺ and Ta²⁴⁺ ions. Empirical results are discussed and give rise to further investigations on the materials.