Future HEP experiment environments will be even higher radiation environment thus, bright, dense, and fast scintillator detectors with excellent radiation hardness are required. With its excellent energy resolution (for the target high energy radiations) and detection efficiency (high density), the CMS PWO calorimeter played an essential role in discovering the Higgs boson via CMS experiments. Of these, the Compact Muon Solenoid (CMS) particle detector (composed of 75,848 PWO scintillators) has a total size of 11 m 3, and is the largest among the used calorimeters. Common inorganic scintillators that compose calorimeters used in HEP experiments include CsI (undoped), BGO, and PbWO 4 (PWO). In HEP, scintillator light yield is secondary, as the energies involved are high, leading to a sufficiently large number of light photon emission during detection. Therefore, characteristics required of detectors in calorimeters include high detection efficiency (density), fast decay time, good energy resolution, and radiation resistance for precise measurements of large numbers of high-energy radiation. The radiation involved in HEP is typically high-energy photons and particles in large numbers (high fluence rate). In HEP, inorganic scintillators are essential for most radiation detectors in calorimeters, both existing and under development. Another scintillator-Ce:LuAP-had an observable photopeak at a temperature of 395 ☌, and the performance at elevated temperatures indicated Ce:LuAP has potential in well-logging applications. Therefore, the Ce:GPS scintillator is expected to show more excellent performance than the Pr:LuAG scintillator in high-temperature environments, including well-logging. However, compared with Ce:GPS, the Pr:LuAG scintillator has a relatively low light yield and possesses intrinsic radioactivity and short peak emission wavelength (306 nm). The light yield of Pr:LuAG, another scintillator known to have excellent temperature resistance, shows only slightly lower light output at 225 ☌ than at 50 ☌. The light yield of Ce:GPS was almost consistent from RT up to approximately 250 ☌. The Ce:GPS scintillator was first introduced in 2007 and is known to have excellent energy resolution, light yield, and temperature dependence. Some of the newly developed oxide scintillators have demonstrated potentials to be used in the well-logging industry. Thus, these two scintillators can replace NaI:Tl scintillator in well-logging, considering that they both have a similar drawback as NaI:Tl of being extremely sensitive to humidity and being very brittle. For example, LaCl 3:Ce maintains an almost constant light yield from 100 to 600 K, reaching its maximum at 500 K. Along with LaBr 3:Ce, 10% doped LaCl 3 showed even more impressive scintillation characteristics over a wide range of temperatures. Regarding temperature resistance, LaBr 3:Ce was reported to show 8% energy resolution at 175 ☌, superior to the 9.9% energy resolution of NaI:Tl at RT. These halide scintillators have received huge attention due to their excellent properties such as excellent light yield, good energy resolution, and high density. The increasing desire for more efficient high-temperature-resistant scintillators has led to the discovery of new halide scintillators, such as LaBr 3:Ce and LaCl 3:Ce, which were first introduced in the early 2000s. In addition, radiation detectors have to operate at high levels of vibration and shock, so the brittleness of the scintillator should also be considered. Therefore, radiation detectors used in the well-logging industry must maintain their performance in terms of scintillation properties (such as emission spectrum, decay time, and light output) at high temperatures. In general, the downhole environment is known to be at a temperature of about 175 ☌ and a pressure of 20,000 psi, and the vibration level and shock level caused by drilling are ~30 g RMS and ~700 g, respectively. Furthermore, in the case of logging while drilling implementations, the radiation detector may experience high levels of vibration and shock. The deeper the well, the harsher the downhole environment (temperature) in which nuclear measurements need to be made. For decades, there has been a steady demand for high-temperature radiation detectors to be used in the well-logging industry, and oil wells need to be drilled deeper to access new fuel sources.
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