Single Crystalline Scintillators Research Articles

Simulation of Electron-Hole Pairs Created by γ-Rays Interaction in Scintillation Crystals Using Geant4 Toolkit

Understanding the electron-hole pair (e-h pair) production process in scintillators is essential for further studies of the scintillation mechanism. The number of e-h pairs can be derived from theoretical and empirical approaches. However, simulation approaches have been chosen to study all the related physical processes and spatial information in scintillation crystals. Due to the complexity of particle interaction and physical properties of solid-state, the simulation approach could be better than the analytical approach. This work aims to develop a Geant4-based simulation toolkit for studying scintillation mechanisms in single-crystalline scintillators since Geant4 can accurately calculate particle energy loss. Due to the lack of a solid-state physic model for insulators, the plasmon creation and phonon loss process for electrons are implemented in the Geant4 toolkit. The electrons, which are created by γ-rays interaction in crystals, can make further ionization to generate secondary electrons or create plasmons, or lose energy to phonons. Then the created plasmons decay into e-h pairs. These electrons and holes are tracked with information on energy and position. Therefore, the number of created e-h pairs and their spatial distribution can be extracted. In this work, we will present the result of the creation process of e-h pairs per MeV in scintillation crystals induced by γ-rays interaction. The number of e-h pairs created by γ ray in some popular inorganic crystals has been calculated. Assuming maximum conversion efficiency from the e-h pair to the luminescence light, we can calculate the maximum light yield of the intrinsic scintillator.

Development of Nd-Doped CaWO4 Single Crystalline Scintillators Emitting Near-Infrared Light

Nd-doped CaWO4 single crystals with dopant concentrations of 0.1, 0.5, and 1% were synthesized by the floating zone method. The transmission, photoluminescence, and scintillation properties were evaluated from ultraviolet to near-infrared (NIR) ranges. An emission peak due to transitions of the host was observed at 400 nm, and several sharp peaks originating from Nd3+ 4f–4f transitions were confirmed at 900, 1060, and 1300 nm. The quantum yields of 0.1, 0.5, and 1% Nd-doped samples were 70.7, 79.5, and 61.2%, respectively, when monitored, and excited wavelengths were 750–1500 nm and 590 nm. Decay times consistent with typical Nd3+ transitions were obtained when NIR ranges were monitored. Additionally, the energy transfer between the host and Nd3+ occurred according to the decay measurement. The relationship between X-ray irradiated dose rate and intensity in the range of NIR was investigated by combining the crystals with an InGaAs-photodiode. The lowest detectable dose rate retaining the linearity of the present crystals was 0.3–0.06 Gy/h.

Effects of dopant concentration in Eu-doped Ca2MgSi2O7 single crystalline scintillators

1–10 % Eu-doped Ca2MgSi2O7 single crystals were synthesized, and photoluminescence and scintillation properties were evaluated to determine the optimal dopant-concentration. A broad peak at 530 nm and a sharp peak at 610 nm are observed in both photoluminescence and scintillation spectra, which are due to Eu2+ and Eu3+, respectively. All the samples show the photoluminescence and scintillation decay due to 5d-4f transitions of Eu2+. All the estimated LY are comparable (10,400–10,700 ph/MeV) when excited by γ-rays from 241Am. The best afterglow level in Eu-doped Ca2MgSi2O7 is 30 ppm, which is much lower than other melilite.

Characterization of Ce-doped RE3Al5O12 (RE=Tb, Dy, Ho, Er, Tm and Yb) single crystalline scintillators

Ce-doped RE3Al5O12 (Ce:REAG, RE=Tb, Dy, Ho, Er, Tm and Yb) single crystals were synthesized by the optical Floating Zone method. The transmittance is approximately 80% in all the samples, and absorptions by rare-earth ions were observed. Under X-ray irradiation, Ce:TbAG, Ce:DyAG, Ce:HoAG and Ce:TmAG exhibit scintillation signals with a broad emission band around 500–700 nm, which is attributable to the 5d–4f transitions of Ce3+. Several emission peaks due to F+ centers and 4f–4f transitions of trivalent rare-earth ions are also observed in some samples. In afterglow properties, Ce:Tb3Al5O12 and Ce:Yb3Al5O12 showed better afterglow levels than the other samples.

First beam loss measurements in the SuperKEKB positron ring using the fast luminosity monitor diamond sensors

SuperKEKB is a very high luminosity ${e}^{+}{e}^{\ensuremath{-}}$ collider consisting of a low energy ring (LER) of positrons of 4 GeV and a high energy ring (HER) of electrons of 7 GeV. The high luminosity will be achieved thanks to the nanobeam scheme, where very strongly focused beams (${\ensuremath{\sigma}}_{y}=60\text{ }\text{ }\mathrm{nm}$) will collide at a large crossing angle of 83 mrad. To maintain high luminosity operation, fast luminosity monitoring is essential in the presence of dynamic instabilities, for feedback and optimization. Fast luminosity monitors consisting of a single crystalline diamond sensor (LAL), a Cherenkov and scintillator detector (KEK) were placed in both rings downstream of the IP (interaction point) to measure the signal from the radiative Bhabha process at zero photon scattering angle ($\ensuremath{\sigma}\ensuremath{\approx}200\text{ }\text{ }\mathrm{mbarn}$). During single beam commissioning of SuperKEKB, the fast luminosity monitors were used as beam loss monitors to measure the single beam losses (beam-gas bremsstrahlung, Touschek scattering, Coulomb scattering). In this paper, a detailed description of the experimental setup, the data acquisition scheme, the data analysis and the comparison with the simulation for the diamond sensors, will be reported.

Growth and luminescent properties of Ce and Eu doped Cesium Hafnium Iodide single crystalline scintillators

In order to obtain new scintillators with high light output and high effective atomic number (Zeff), we performed anion-substitution for Cs2HfCl6 (CHC) scintillator, and then, we succeeded in growing Cs2HfI6 (CHI) single crystalline scintillator. It had Zeff of 58, which is the same as that of CHC, and had high light output of ∼70,000 photons/MeV with 700 nm emission. However, its scintillation decay time of ∼2.5 µs was slow for practical use as gamma-ray monitor. In this study, we performed Ce3+/Eu2+ doping to Hf4+ site to improve decay time of CHI, introducing the fast 5d-4f luminescence. Ce:CHI and Eu:CHI single crystals were finally obtained by the vertical Bridgman-Stockbarger method. The luminescence spectra of the Ce:CHI and Eu:CHI were very similar to that of the non-doped CHI, which would mean that no 5d-4f luminescence of Ce3+/Eu2+ was observed. The measured light output and decay time of Ce:CHI were ∼48,000 photon/MeV and 2.3 ± 0.1 µs, respectively. As for Eu:CHI, light output and decay time were ∼69,000 photon/MeV and 2.8 ± 0.1 µs, respectively.

Luminescence properties of Nd3+ doped LiLuF4 single crystals with different dopant concentrations

Nd-doped LuLiF4 single crystalline scintillators with different Nd concentrations of 1%, 2%, 3%, and 4% were grown by the micro-pulling-down (μ-PD) method and that of Nd 1% were grown by the Czochralski method. There are some absorption bands due to Nd3+ 4f–4f transitions in the spectra and these lines correspond to the transitions from the ground state 4I9/2 to the excited states. In photo- and radio-luminescence spectra, Nd3+ 4f–4f transition peaks were observed. The photoluminescence decay time for 4D3/2→4I13/2 transition showed approximately 0.75μs and slow component. The highest light yield was estimated to be 700photon/MeV for LuLiF4:Nd2% crystal grown by the μ-PD method.

Growth and scintillation properties of (Lu1 − Tm )2SiO5 [x = 0.001, 0.01, 0.1, 1

(Lu 1 − x Tm x ) 2 SiO 5 ( x = 0.001, 0.01, 0.1, 1) single crystalline scintillators were grown by the μ-PD method. In transmittance measurement, absorption bands due to Tm 3+ 4f–4f transitions were observed at 260, 292, 356, 463, 680 and 790 nm and they could be ascribed to the transition from the 3 H 6 ground state to its excited states, 1 I 6 , 3 P 6 , 1 D 2 , 1 G 4 , 3 F 3 and 3 H 4 , respectively. Strong emission peak due to 1 D 2 → 3 F 4 transition of Tm 3+ was shown at 453 nm under X-ray irradiation. Photoluminescence decay time constant caused by this transition were evaluated to be 11.9 μs. Tm 1% doped one exhibited the highest light yield of 3530 ± 200 photons/MeV when excited by 137 Cs gamma-ray exposure. ► (Lu 1 − x Tm x ) 2 SiO 5 single crystals were grown by the μ-PD method. ► The Tm 3+ 4f–4f emission and absorption lines were observed. ► The scintillation decay times were evaluated as 11.9–13.5 μs. ► Pulse height measurements showed the 1% Tm sample had the highest light yield. ► Quenching was observed in higher Tm concentration.

Performance of thin long scintillator strips of GSO:Ce, LGSO:Ce and LuAG:Pr for low energy γ-rays

Interest in fibers or strips of single crystalline scintillators is increasing for their possible applications in fine-segmented particle detectors for particle physics experiments as well as γ-ray detectors for medical diagnoses. We compared 2×2×100mm3 strips of Gd2SiO5(GSO):Ce, Lu1.9Gd0.1SiO5 (LGSO):Ce, and Lu3Al5O12(LuAG):Pr single crystals for 0.511MeV γ-rays with respect to the effective light attenuation length λa, light yield LY, FWHM energy resolution ΔE/E and rms position resolution σ(z) of the injection position z along the length. The obtained result was (λa, LY, ΔE/E, σ(z))=(128mm, 380phe/MeV, 17.7%, 8.7mm) in GSO:Ce, (509mm, 1760phe/MeV, 12.2%, 10.9mm) in LGSO:Ce, and (171mm, 690phe/MeV, 15.0%, 8.9mm) in LuAG:Pr. The z position was obtained independently from the pulse height ratio as well as the timing difference between both ends of the strip. The latter method gave comparable or even smaller σ(z) than the former only in LGSO:Ce having both large LY and fast rise time. The λa in the 100mm long GSO:Ce strip was found to be twice as large as that in the 200mm long one [1] with the same cross-section. To obtain good ΔE/E and σ(z), large light yield, fast rise time, and moderately large attenuation length are important for the scintillators.

Structural and morphological characteristics of yttrium and lutetium orthoborates synthesized in thin layers of borate oxide glasses

Abstract

Crystal growth and scintillation properties of Er-doped Lu 3Al 5O 12 single crystals

Er-doped Lu 3Al 5O 12 (Er:LuAG) single crystalline scintillators with different Er concentrations of 0.1, 0.5, 1, and 3% were grown by the micro-pulling-down (μ-PD) method. The grown crystals were composed of single-phase material, as demonstrated by powder X-ray diffraction (XRD). The radioluminescence spectra measured under 241Am α-ray excitation indicated host emission at approximately 350 nm and Er 3+ 4f–4f emissions. According to the pulse height spectra recorded under γ-ray irradiation, the 0.5% Er:LuAG exhibited the highest peak channel among the samples. The γ-ray excited decay time profiles were well fitted by the two-component exponential approximation (0.8 μs and 6–10 μs).

Investigations of optical and scintillation properties of Tm 3+-doped YAlO 3

Pure, 0.1, 0.5 and 1 mol% Tm-doped YAP single crystalline scintillators were grown by the μ-PD method. The XRD analysis confirmed the lattice constants decrease with the Tm concentration. In the transmittance measurement, the absorption bands due to the Tm 3+ 4f–4f transitions were observed at 265, 360, 485, 690 and 800 nm and they were ascribed to the transition from the 3H 6 ground state to its 1I 6, 1D 2, 1G 4, 3F 3 and 3H 4 excited states, respectively. Strong emission peak due to the 1I 6– 3F 4 transition of Tm 3+ appeared at 350 nm under X-ray irradiation. The photoluminescence decay time constants related to this transition were evaluated to be from 15.3 to 17.3 μs and the scintillation decay time constants under gamma-ray excitation were estimated to be from 17.5 to 18.8 μs. The Tm 1% doped crystal exhibited the highest light yield of 15, 100 ± 1500 photons/MeV when excited by 137Cs gamma-ray radiation.

Basic study of Europium doped LiCaAlF 6 scintillator and its capability for thermal neutron imaging application

Eu 2+ 0.1, 0.5, 1, and 2 mol% doped LiCaAlF 6 single crystalline scintillators were grown by the micro-pulling down (μ-PD) method. Eu 2+ 2 mol% doped LiCaAlF 6 was also prepared using the Czochralski method. In the transmittance spectra, 4f–5d absorption lines appeared around 200–220 and 290–350 nm. An intense emission at 375 nm due to Eu 2+ 5d–4f transition was observed under 241Am α-ray excitation. When 252Cf excited pulse height spectra were measured, Eu 2% doped one showed the highest light yield of 29,000 ph/n with 1.15 μs decay time. Using the 2 inch φ Czochralski grown one coupled with the position sensitive photomultiplier tube covered by Cd mask with various size (1, 2, 3, and 5 mm) pin holes, thermal neutron imaging was examined. As a result, the spatial resolution turned out to be better than 1 mm.

Development of ZnO Based Charged Particle Monitor for Processing Facility

In the present paper, we describe the development of an α-ray imaging detector based on a ZnO single crystalline scintillator and a position-sensitive photomultiplier tube (PSPMT). The ZnO crystal was grown by the hydrothermal synthesis method with 2-in.-φ in diameter. The ZnO specimen was polished out to be 0.5 mm in thickness. After optically coupling with PSPMT, the crystal was irradiated with 241Am α-ray for evaluation of both spatial resolution and pulse height spectrum. Using the charge center of the gravity method, two-dimensional α-ray images were successfully obtained. The efficiency of the energy window in terms of imaging quality was also examined.

Optical properties and gamma-ray response of Czochralski grown Pr:Lu3Al5O12 scintillating garnet crystals with different Pr content

Pr:LuAG single crystalline scintillators with different Pr3+ concentration, 0.1, 0.18, and 0.22mol% were grown by the Czochralski method. The crystals were cut to dimensions of 2.2×2.2×15mm3 and polished, simulating sensors for Positron Emission Tomography (PET). Their absorption coefficients were examined, and the absorption strength was found to be proportional to the Pr concentration. The α-ray induced emission spectra of the samples demonstrated two emission lines peaking at 310 and 370nm. The emission intensities in the radio luminescence spectra were also proportional to the Pr content. The absolute light yields and intrinsic energy resolution under γ-ray irradiation were evaluated at +20, 0, and −20°C using avalanche photodiode as a photodetector. Pr 0.22% doped crystal had strongest light output of 16400ph/MeV, and its intrinsic energy resolution was around few % at several hundred keV. When coupled with PMT, the decay time was around 25ns, and it was almost independent on concentration.

Growth and scintillation properties of Pr doped YAP with different Pr concentrations

Pr 3+ 0.2, 0.75, and 3 mol% doped YAP single crystalline scintillators were grown by using the micro-pulling down (μ-PD) method. Pr 3+ 0.05 mol% doped YAP was also prepared by using the Czochralski method. In transmittance spectra, 4f–5d absorption line appeared at 230 nm. The μ-PD grown crystals showed intense emission at 290 nm while the Czochralski grown one showed an emission peak at 245 nm in radio luminescence spectra under X-ray excitation. Among them, the Czochralski grown one exhibited the highest light yield under 137Cs 662 keV excitation and the absolute light yield of this sample was estimated to be 20400±2000 ph/MeV. The decay time constants of these scintillators were around 10 ns due to Pr 3+ 5d–4f transition.

Growth and scintillation properties of BaMgF4

By using the micro-pulling down (μ-PD) method, the barium magnesium fluoride (BaMgF4) single crystalline scintillator was produced. The crystal was cut and mirror polished to the physical dimensions of 1×2×10mm3 for examination of scintillation properties. BaMgF4 demonstrated ∼70% transmittance in wavelength range above 170nm, and strong emission peaking around 205nm was observed under X-ray excitation. The absolute light yield of BaMgF4 was 1300±100ph/MeV, and the decay time profile showed two components as 0.57±0.01 (70%) and 2.2±0.31 (30%)ns at room temperature.

Growth, Optical Properties, and Scintillation Light Yield of CaF2:Ce Crystals with Different Ce Concentration

Present work describes the first detailed γ-ray light yield of Ce3+ perturbed emission in CaF2 host. (1-, 3-, 5-, 10-, and 20-mol %-) Ce3+-doped single crystalline CaF2 scintillator crystals were grown by the micro-pulling-down method. Their transmittances were measured to be approximately 80% at UV to visible wavelengths. All the crystals exhibited emission peaks at approximately 330 nm, which were identified as the Ce3+ perturbed emission, when they were irradiated by 1 GBq 137Cs. The photoluminescence decay kinetics was measured to be about 40 ns for all the crystals. Scintillation light yield in unit of photons/MeV (ph/MeV) was measured, and the 5% sample showed the highest light yield of around 900 ph/MeV with 2 µs shaping time.

Transport and Recombination of Charge States in Organic Single Crystalline and Polycrystalline Scintillators

Studies of some aspects of the processes of transport and recombination of charge states in organic scintillation crystals which differ in theirs structural peculiarities are presented.

The non-proportional response of single crystalline oxide scintillators

The energy dependence of the response of single crystalline oxide scintillators (BGO, CWO and GSO(Ce)) was studied over the wide energy range from 6 to 1332 keV. The non-proportionality was defined as the difference between the specific response value at the given energy and the one at 661.6 keV. It is found that a considerable (up to 35%) non-proportionality of the response exists for the all investigated scintillators in the low energy region from 6 to 100 keV, while as in the energy range from 100 to 1332 keV the scintillator's response is proportional to the gamma-rays energy with the accuracy equal to /spl plusmn/1%.