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Because of its fast scintillation peaked at 220 nm with a decay time of less than 0.6 ns, barium fluoride crystals have attracted broad interest in the community pursuing ultrafast detectors for future high energy physics (HEP) experiments and GHz hard X-ray imaging for future X-ray free-electron laser (XFEL) facilities. A crucial issue for its application is the spectral response of photodetectors down to vacuum ultraviolet (VUV). In this article, we compare quantum efficiency (QE) and photon detection efficiency (PDE) spectra measured for several ultraviolet (UV) photodetectors down to 200 nm. Their figures of merit on the detection efficiency for the fast component and the suppression of the slow component are also discussed. [ABSTRACT FROM AUTHOR]

Because of their potential low cost, bright light, and fast decay time, LuAG:Ce ceramic scintillators have attracted a broad interest in the high-energy physics community. One crucial issue for their application in future high-energy physics experiments is their radiation hardness against neutrons and protons expected at future hadron colliders. We report optical and scintillation performance of 1-mm LuAG:Ce ceramic samples doped with Mg2+ (and Ca2+) and their radiation damage induced by hadrons. While Mg2+ co-doping improves their light output, Ca2+ co-doping improves their fast to total (F/T) ratio. LuAG:Ce ceramic samples were irradiated at the Los Alamos Neutron Science Center (LANSCE), Los Alamos, NM, USA, by neutrons up to $6.7\times 10^{15}\,\,\text{n}_{\mathrm {eq}}$ /cm2 and by 24-GeV and 800-MeV protons at CERN PS-IRRAD up to $1.2\times 10^{15}$ p/cm2 and at LANSCE up to $2.3\times 10^{14}$ p/cm2, respectively. All samples show excellent radiation hardness with more than 90% of light after irradiation. The RIAC values induced by neutrons are found to be a factor of 2 smaller than lutetium–yttrium oxyorthosilicate (LYSO:Ce) crystals. The RIAC values induced by protons are also found a factor of 2 smaller than LYSO:Ce crystals in LuAG:Ce ceramic samples with good optical quality. Research and development will continue to develop LuAG:Ce scintillating ceramics with improved optical quality for future investigation. [ABSTRACT FROM AUTHOR]

Lu2(1–x)Y2xSiO5 (LYSO) crystals readout by a silicon photomultiplier (SiPM) will be used in the barrel timing layer of a precision timing detector for the Compact Muon Solenoid (CMS) experiment at the High-Luminosity Large Hadron Collider (HL-LHC). This detector is expected to be exposed up to 5-Mrad γ-ray dose, 2.5 × 1013 charged hadrons/cm2, and 3 × 1014 neq/cm2 at the HL-LHC for 10 years of operation. We present results of the photocurrent in LYSO+SiPM packages induced by Co-60 γ-rays and Cf-252 neutrons of the expected dose rate and neutron flux, respectively. The γ-ray-induced readout noise is about 30 keV, which is negligible when compared to the 4.2-MeV signal from the minimum ionization particle signals. The neutron-induced readout noise is about 7 keV, which is more than a factor of 4 smaller than that from the γ-rays. [ABSTRACT FROM AUTHOR]

One crucial issue for the application of scintillation crystals in future high-energy physics experiments is radiation damage in a severe radiation environment, such as the high luminosity large hadron collider. While radiation damage induced by ionization dose in inorganic scintillators is well understood, investigations are ongoing to understand radiation damage induced by hadrons, including both charged hadrons and neutrons. Aiming at understanding neutron-induced radiation damage in fast inorganic scintillators, lutetium yttrium oxyorthosilicate (LYSO)/lutetium fine silicate (LFS), BaF2, and PWO crystals were irradiated at Los Alamos Neutron Science Center by a combination of particles, including neutrons, protons, and γ-rays. The results indicate that LYSO/LFS and BaF2 crystal plates are radiation hard up to a 1-MeV equivalent neutrons fluence of 9 × 1015 equivalent neutron (neq)/cm2, but not PWO, and the neutron-induced radiation damage in LYSO crystals is a factor of ten less than protons. [ABSTRACT FROM AUTHOR]

Gigahertz hard X-ray imaging presents an unprecedented challenge to both timing and spatial resolutions for inorganic scintillator-based front imagers. A beam test with 30-keV X-rays from the Advanced Photon Source (APS) showed that 5-mm BaF2 plates resolve well 30-keV X-ray septuplets of 27-ps width and 2.83-ns spacing. Pixelated crystal screens with a pitch down to 400~μm were fabricated by mechanic slicing for BaF2, BaF2:Y, and LYSO crystals. Their spatial resolution and detection efficiency for hard X-rays are defined by the pitch and thickness, respectively. Thicker monolithic crystal screens show poorer spatial resolution, which may be improved using a small optical aperture with a loss in both efficiency and dynamic range for hard X-rays. Future plans include pursuing smaller crystal pitches by laser slicing and research and development on novel ultrafast inorganic scintillators. [ABSTRACT FROM AUTHOR]

Because of their ultrafast scintillation with subnanosecond decay time, barium fluoride (BaF2) crystals have attracted broad interest in the high energy physics and nuclear physics communities. One crucial issue, however, is its slow scintillation component with 600-ns decay time, which causes pile-up in a high rate environment. Previous studies show that the slow component can be suppressed effectively by rare earth doping. In this paper, we report investigations on a set of $\Phi \,\,18\times21$ mm3 BaF2 cylinders doped with different yttrium levels grown at Beijing Glass Research Institute (BGRI), from which the optimized yttrium doping level was determined. $\text{A}\Phi \,\,40\times160$ mm3 BaF2 ingot with 5 atomic % (at.%) yttrium doping was consequently grown at BGRI and was used to cut one $25\times 25\times100$ mm3 crystal and several thin slices. Their optical and scintillation properties were measured at Caltech. The results show that yttrium doping effectively suppresses the slow component while maintaining its ultrafast light unchanged. Research and development will continue to develop large-size BaF2:Y crystals with improved optical quality for a fast BaF2:Y crystal calorimeter for Mu2e-II. [ABSTRACT FROM AUTHOR]

Gigahertz hard X-ray imaging for the proposed matter-radiation interaction in extreme project presents an unprecedented challenge to front imager in both speed and radiation hardness. Novel fast scintillators are to be developed to face these challenges. This paper presents an investigation on the optical and scintillation properties for a set of fast inorganic scintillators. Transmittance, emission, light output, and decay time were measured. Based on this investigation, we plan to take two approaches to develop inorganic scintillators with subnanoseconds of decay time for the gigahertz hard X-ray imaging. One is yttrium-doped barium fluoride single crystals, and another is based on gallium-doped ZnO nanoparticles. [ABSTRACT FROM AUTHOR]

Future high-energy physics experiments at the energy and intensity frontiers will face a challenge of severe radiation environment from both ionization dose and charged and neutral hadrons. The high-luminosity large hadron collider, for example, will present an environment, where up to 130 Mrad ionization dose, 3 \times 10^14 charged hadrons/cm2 and 5 \times 10^15 neutrons/cm2 are expected. In this paper, we report our investigation on charged hadron-induced radiation damage in BaF2, LYSO/LFS, and PWO crystals up to 3 \times 10^15 protons/cm2 by using 800-MeV protons at the Los Alamos Neutron Science Center. Comparison is made between radiation damages induced by protons and ionization dose alone. [ABSTRACT FROM AUTHOR]

Because of its fast scintillation and low cost, undoped CsI crystal has been used to construct crystal calorimeters for high-energy physics experiments. Undoped CsI crystal samples from three vendors were investigated at the Caltech Crystal Laboratory. In addition to the 30-ns fast scintillation peaked at 310 nm, a slow scintillation component peaked at 450 nm was found with a decay time of a few microseconds. The intensity of the slow component may be varied from the seed to the tail end, so it affects crystal’s light response uniformity. It was also found that the slow component is highly correlated with the radiation-induced readout noise and may be eliminated spectroscopically by using an optical filter. The slow component is believed to be related to impurities and/or defects in the crystal. [ABSTRACT FROM AUTHOR]

In addition to La-doped barium fluoride (BaF2) crystals, La/Ce co-doped BaF2 crystals were also investigated at the California Institute of Technology, Pasadena, CA, USA. Strong cerium-induced emissions peaked at 305 and 320 nm with a decay time of 25 ns were observed, in addition to the fast and slow scintillation at 220 and 300 nm, respectively. The La/Ce co-doping was also found effective in suppressing the slow component in BaF2. Compared to La-doped crystals, the La/Ce co-doped crystals have a better light output in both 50- and 2500-ns gate. The fast/slow ratio of La/Ce co-doped crystal was found to be about 1/1, similar to La-doping, which is also considered not sufficient for pile-up suppression. A 20-cm-long La/Ce co-doped BaF2 crystal shows also excellent optical quality and light response uniformity. [ABSTRACT FROM AUTHOR]

Because of its fast scintillation component with subnanosecond decay time, BaF2 crystals are considered as a candidate for ultrafast crystal calorimeters for future high energy physics experiments at the energy and intensity frontiers. Undoped BaF2, however, has a slow scintillation component with 600 ns decay time, which causes pile-up. In the part I of this paper, we report investigations on La doping in BaF2 crystals to suppress the slow component. While typical fast/slow (F/S) ratio observed in undoped BaF2 is 1/5, La-doped BaF2 crystals were found to improve this ratio to about 1/1. The overall F/S ratio, however, is considered not sufficient for pile-up suppression. [ABSTRACT FROM AUTHOR]