CERN,1211 Geneve 23, Switzerland.
UniMIB,Piazza dell'Ateneo Nuovo, 1-20126, Milano, Italy.
Phys Med Biol. 2021 Jun 4;66(11). doi: 10.1088/1361-6560/abf476.
Inorganic scintillators are widely used for fast timing applications in high-energy physics (HEP) experiments, time-of-flight positron emission tomography and time tagging of soft and hard x-ray photons at advanced light sources. As the best coincidence time resolution (CTR) achievable is proportional to the square root of the scintillation decay time it is worth studying fast cross-luminescence, for example in BaFwhich has an intrinsic yield of about 1400 photons/MeV. However, emission bands in BaFare located in the deep-UV at 195 nm and 220 nm, which sets severe constraints on photodetector selection. Recent developments in dark matter and neutrinoless double beta decay searches have led to silicon photomultipliers (SiPMs) with photon detection efficiencies of 20%-25% at wavelengths of 200 nm. We tested state-of-the-art devices from Fondazione Bruno Kessler and measured a best CTR of 51 ± 5 ps full width at half maximum when coupling 2 mm × 2 mm × 3 mm BaFcrystals excited by 511 keV electron-positron annihilation gammas. Using these vacuum ultraviolet SiPMs we recorded the scintillation kinetics of samples from Epic Crystal under 511 keV excitation, confirming a fast decay time of 855 ps with 12.2% relative light yield and 805 ns with 84.0% abundance, together with a smaller rise time of 4 ps beyond the resolution of our setup. The total intrinsic light yield was determined to be 8500 photons/MeV. We also revealed a faster component with 136 ps decay time and 3.7% light yield contribution, which is extremely interesting for the fastest timing applications. Timing characteristics and CTR results on BaFsamples from different producers and with different dopants (yttrium, cadmium and lanthanum) are given, and clearly show that the the slow 800 ns emission can be effectively suppressed. Such results ultimately pave the way for high-rate ultrafast timing applications in medical diagnosis, range monitoring in proton or heavy ion therapy and HEP.
无机闪烁体广泛应用于高能物理（HEP）实验中的快速定时应用、飞行时间正电子发射断层扫描和先进光源中软x 射线和硬 x 射线光子的时间标记。由于可实现的最佳符合时间分辨率（CTR）与闪烁衰减时间的平方根成正比，因此值得研究快速交叉发光，例如在 BaF 中，其固有产率约为 1400 个光子/MeV。然而，BaF 的发射带位于深紫外区的 195nm 和 220nm，这对光电探测器的选择构成了严格的限制。暗物质和中微子无双β衰变搜索的最新发展导致了具有 200nm 处 20%-25%光子探测效率的硅光电倍增管（SiPM）。我们测试了 Fondazione Bruno Kessler 的最先进设备，并在将 511keV 电子-正电子湮没伽马激发的 2mm×2mm×3mm BaF 晶体耦合时测量了最佳 CTR 为 51±5ps 半高全宽。使用这些真空紫外 SiPM，我们记录了 Epic Crystal 样品在 511keV 激发下的闪烁动力学，证实了 855ps 的快速衰减时间，相对光输出为 12.2%，丰度为 805ns，同时上升时间为 4ps，超出了我们设置的分辨率。总固有光输出确定为 8500 个光子/MeV。我们还揭示了具有 136ps 衰减时间和 3.7%光输出贡献的更快组件，这对于最快的定时应用非常有趣。给出了来自不同制造商和具有不同掺杂剂（钇、镉和镧）的 BaF 样品的定时特性和 CTR 结果，清楚地表明可以有效抑制缓慢的 800ns 发射。这些结果最终为医疗诊断中的高速超快定时应用、质子或重离子治疗和 HEP 中的射程监测铺平了道路。
