Rihua Mao

Optical and Scintillation Properties of Inorganic Scintillators in High Energy Physics

This paper presents a comparative study of optical and scintillation properties for various inorganic crystal scintillators, which are used, or actively pursued, by the high energy physics community for experiments. Transmittance, excitation and photo-luminescence spectra were measured for samples with a dimension of 1.5 radiation length. The transmittance data are compared to the theoretical limit calculated by using refractive index, assuming no internal absorption. Refractive index of lutetium oxyorthosilicate and lutetium-yttrium oxyorthosilicate was measured by using a V-prism. Light output was measured for these samples with Tyvek paper wrapping, and the result is presented with the quantum efficiency of the readout devices taken out. Temperature coefficient of the light output was also measured. The result of these measurements will be used in the summary table of the inorganic scintillator section for the 2008 edition of the particle data book.

Optical and scintillation properties of inorganic scintillators in high energy physics

This paper presents a comparative study of the optical and scintillation properties for various inorganic crystal scintillators commonly used in high energy physics experiments. Transmittance, excitation and photo-luminescence spectra were measured for samples with a dimension of 1.5 X0. The transmittance data are compared to the theoretical limit calculated by using refractive index, assuming no internal absorption. Refractive index of lutetium oxyorthosilicate and lutetium-yttrium oxyorthosilicate was measured by using a V-prism. Light output was measured for these samples with Tyvek paper wrapping, and the result is presented with the quantum efficiency of the readout devices taken out. Temperature coefficient of the light output was also measured. The result of these measurements will be used in the summary table of the inorganic scintillator section for the 2008 edition of the particle data book.

Gamma-Ray Induced Radiation Damage in Large Size LSO and LYSO Crystal Samples

This paper presents a study of the gamma-ray induced radiation damage effect in large size (2.5 times 2.5 times 20 cm3) LSO and LYSO crystal samples. Optical and scintillation properties, including longitudinal transmittance and photo-luminescence spectra, light output and light response uniformity with PMT and APD readout, are measured before and after gamma-ray irradiations with an integrated dose up to 106 rad for three LSO and LYSO samples from different vendors. It was found that 300degC thermal annealing removes all radiation induced absorption. The photo-luminescence spectra measured before and after the irradiations were found to be consistent, indicating that the scintillation mechanism is not damaged. The radiation damage recovers very slow under the room temperature, indicating that the radiation damage level in LSO and LYSO crystals is not dose rate dependent. It was also found that the overall radiation damage in LSO and LYSO crystals is small as compared to other crystal scintillators commonly used in high energy and nuclear physics experiments.

Emission Spectra of LSO and LYSO Crystals Excited by UV Light, X-Ray and

Because of their high stopping power (Xo = 1.14 cm, RMoliere = 2.07 cm) and fast (~ 40 ns) bright (4 times of BGO) scintillation, cerium doped lutetium oxyorthosilicate (LSO) and cerium doped lutetium-yttrium oxyorthosilicate (LYSO) crystals have attracted a broad interest in the high energy physics community. This paper presents a comparative study on emission spectra measured for large size BGO, lead tungstate (PbWO4), LSO and LYSO samples excited by UV light (photo-luminescence) with and without internal absorption, X-ray (X-luminescence) and gamma-ray (radio-luminescence). A red shift was observed between the emission spectra with internal absorption as compared to that without. An additional red shift and a significant red component were observed in the radio-luminescence spectra measured for LSO samples but not LYSO samples, which were disappeared after a gamma-ray irradiation with an accumulated dose of 5 x 103 rad. This is the only significant difference observed between the large size LSO and LYSO samples. The origin of these red shifts and the consequence to their light output and applications in the high energy and nuclear physics experiments are discussed.

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Because of their high stopping power (X0=1.14 cm), fast (τ = 40 ns) bright (4 times BGO) scintillation with small temperature coefficient (-0.2%/°C) and superb radiation hardness, LSO/LYSO crystals are chosen to construct electromagnetic calorimeters (ECAL) of total absorption nature. One critical issue for this application is the light response uniformity (LRU) of long crystal bars with tapered geometry, which is affected by the non-uniform light yield along the crystal, the self-absorption and the optical focusing effect. Following a ray-tracing simulation study, an uniformization method was developed by roughening one side surface with LRU of better than 3% achieved. LSO/LYSO crystals are also proposed as the active material for a sampling ECAL for future HEP experiments in severe radiation environment. Preliminary designs with Pb or W absorber are described. Measurements of light collection efficiency (LCE) for prototype Shashlik cells with wavelength shifting fiber readout are presented. Future development on LSO/LYSO crystal based sampling ECAL is discussed.

-ray

Because of their high stopping power (Xo = 1.14 cm RMoiiere = 2.07 cm) and fast (~40 ns) bright (4 times of BGO) scintillation, cerium doped lutetium oxyorthosilicate (LSO) and cerium doped lutetium-yttrium oxyorthosilicate (LYSO) crystals have attracted a broad interest in the high energy physics community. This paper presents a comparative study on emission spectra measured for large size BGO, lead tungstate (PbWO4) LYSO and LSO samples excited by UV light (photo-luminescence), x-ray (x- luminescence) and gamma-ray (radio-luminescence). A red shift was observed between the x-luminescence and the radio-luminescence versus the surface photo-luminescence, which can be explained by internal absorption. Additional red shift and significant red component was observed in the radio-luminescence spectra measured for LSO samples. This is the only significant difference we observed between the large size LSO and LYSO samples. The origin of these red shifts and the consequence to their light output and applications in the high energy and nuclear physics experiments are elaborated.

LSO/LYSO Crystals for Calorimeters in Future HEP Experiments

Because of the broad interest in high energy and nuclear physics community, mass production capacities of lead tungstate crystals have been established. The optical and scintillation properties of lead tungstate crystals, 20 each from two major vendors, were evaluated. The transmittance, emission and excitation spectra, light output and light response uniformity of these samples were measured. The degradations of these properties under irradiation, and the emission weighted radiation induced absorption coefficient (EWRIAC) were also studied. It was found that currently mass-produced lead tungstate crystals are radiation hard enough for radiation environments where expected dose rates do not exceed a few hundred rad/h.

Emission spectra of LSO and LYSO crystals excited by UV light, x-ray and γ-ray

Because of their high stopping power (X_0 = 1.14 cm), fast (t = 40 ns) and bright (4 times of BGO) scintillation and good radiation hardness, cerium doped silicate based heavy crystal scintillators (LSO and LYSO) have attracted a broad interest in the high energy physics community pursuing precision electromagnetic calorimeter in severe radiation environment. We present in this paper current status of large size LSO and LYSO crystals adequate for HEP applications. The optical and scintillation properties and their radiation hardness are discussed.

Quality of mass-produced lead tungstate crystals

Crystal calorimeter has traditionally played an important role in precision measurement of electrons and photons in high energy physics experiments. Recent interest in calorimeter technology extends its application to measurement of hadrons and jets with dual readout for both Cherenkov and scintillation light. Optical and scintillation properties of crystal scintillators commonly used in particle physics experiments are reviewed. Technologies to discriminate Cherenkov and scintillation light is elaborated. Candidate crystals for the homogeneous hadronic calorimeter detector concept and their recent development are discussed.

LSO/LYSO Crystals for Future HEP Experiments

Neutron induced nuclear counter effect in Hamamatsu silicon PIN diodes and APDs was measured by irradiating fast neutrons from a pair of 252Cf sources directly to these devices. It was found that the entire kinetic energy of these neutrons may be converted into electron signals in these devices, leading to anomalous signals of up to a few million electrons in a single isolated calorimeter readout channel. Signals of such amplitude represent equivalent energy of several hundred GeV and a few GeV for PWO and LSO/LYSO crystals respectively assuming the corresponding light yields of 4 and 800 p.e./MeV. The overall rate of the neutron induced nuclear counter effect in APDs is found to be more than an order of magnitude less than that in PIN diodes. Increasing the APD gain was also found to reduce the neutron induced nuclear counter effect. An intelligent front-end chip capable of selecting un-contaminated signal is proposed to eliminate completely the nuclear counter effect without significant cost increase.