title: Fast scintillating ZnO ceramics for relativistic heavy-ion beam diagnostics
Creators: name: Saifulin, Maxim
Publisher: name: UNSPECIFIED
Year: 2024

description: This thesis focuses on the study of inorganic scintillating ceramics based on zinc oxide prepared by uni-axial hot pressing in vacuum and doped with different elements such as indium and gallium. The optical and luminescent properties of these samples were tested under heavy-ion irradiation. The investigations are motivated by the need to eventually replace plastic scintillators, which are currently standard for beam diagnostics in fast-counting scintillation detectors but suffer severely from radiation damage. ZnO-based ceramic scintillation detectors are expected to be radiation hard and as such particularly suitable for beam diagnostics at heavy-ion accelerator facilities for absolute beam intensity measurements and calibration of beam current measuring devices such as ionization chambers and secondary electron transmission monitors.

The ion irradiation experiments were performed at the universal linear accelerator UNILAC and at the heavy-ion synchrotron SIS18 of the GSI Helmholtz Center for Heavy Ion Research (Darmstadt, Germany). The ceramic samples were irradiated under various beam conditions, including ions between 40Ar and 238U ions, beam energies from 4.8 to 500 MeV/u, and fluences up to 10^13 ions/cm^2. The light output and emission spectra of ion-induced luminescence were recorded in-situ during sample irradiation.

Under all beam conditions, the intensity of the luminescent light decreases with increasing ion fluence. The evolution of the light intensity as a function of fluence is described with the model suggested by Birks and Black, yielding the critical fluence of 50% intensity loss for the stopping powers of the respective ions. The ZnO-based ceramics show more than 100 times higher radiation hardness compared to standard plastic scintillators used in heavy-ion beam diagnostics. Non-irradiated In-doped and Ga-doped ZnO ceramics exhibit intense exciton-related near-band-edge emission combined with very low defect-related deep-level emission.

When exposed to heavy ions, the intensity of the near-band-edge emission decreases, but no new emission bands associated with radiation-induced defects are observed. In-situ optical light transmission measurements were performed in the wavelength range of 300 to 1000 nm. With increasing ion fluence, the spectra show a more and more pronounced reduction in transmission in the 390-600 nm range, while no change is observed at higher wavelengths. Important to note is that the ionoluminescence intensity decreases faster than the optical transmission. The kinetics of luminescent light emission was characterized using fast photomultiplier tube signals. Before ion exposure, both In-doped and Ga-doped ZnO ceramics exhibit ultrafast scintillation decay times of less than a nanosecond. No change in scintillation decay time is observed as a result of ion irradiation.

The second part of the thesis concentrated on the design and construction of a prototype ZnO(In) based scintillation detector. The performance of this prototype was tested with various 300 MeV/u ions (40Ar-238U) including a variation of the beam spot position across the active area of the prototype detector. Compared to the plastic reference detector, the ZnO ceramic prototype showed 100% counting efficiency. Considering the radiation hardness results, the ceramic detector is expected to have an operational lifetime at least 100 times longer than the plastic scintillation detectors currently used for beam diagnostics at GSI. The new detector prototype represents a tool with significantly improved properties for heavy-ion beam diagnostics.