Improvement of the Time Resolution of Radiation Detectors Based on Gd₃Al₂Ga₃O₁₂ Scintillators With SiPM Readout

Abstract

Coincidence time resolution (CTR) of scintillation detectors based on Ce- and Mg-codoped Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> (GAGG) scintillation crystals and high-density silicon photomultipliers (SiPMs) is shown to be 165 ps (full width at half maximum) for 511-keV <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula> -quanta, approaching that achieved by using LSO scintillators. To study the prospective for further improvement of the time resolution, the population of the emitting Ce centers was investigated by optical pump and probe technique using selective photoexcitation and probing by a white light continuum with subpicosecond time resolution. The importance of free electron trapping for excitation transfer to emitting Ce ions was revealed. The influence of transfer delay on the scintillation response time is described, and the dynamics of electron relaxation to the lowest excited level of Ce ion is studied experimentally and analyzed by taking into account intracenter relaxation and relaxation via conduction band. The influence of electron diffusivity on the rise time of the population of the emitting level is described. It is shown that codoping of GAGG:Ce by magnesium even at the level as low as 10 ppm efficiently decreases the scintillator response time by enhancing the electron diffusivity.