Scintillation Spectra Research Articles

Near-infrared scintillation properties of Nd-doped CaYAl3O7 single crystals

We prepared Nd-doped CaYAl3O7 single crystals with different Nd concentrations of 0.1, 0.5, 1.0, 5.0, 10, and 20% by the floating zone method. Photoluminescence (PL) and scintillation properties of all the samples were investigated, and the performance as near-infrared (NIR) scintillators was evaluated. All the samples exhibited some luminescence peaks of 4f-4f transitions of Nd3+ in PL and scintillation spectra at around 890, 1060, and 1300 nm. The 5.0% Nd-doped sample showed the highest PL quantum yield of 49.5%. In addition, the 5.0% Nd-doped sample had the highest scintillation intensity under X-ray irradiation among the samples, and the lowest detectable dose rate was 0.001 Gy/h.

Ultraviolet–near infrared luminescence characteristics of Nd:La2Be2O5 single crystals for near-infrared emitting scintillators

The fabrication of 0.1, 0.5, 1.0, and 5.0 % Nd:La2Be2O5 single crystals was carried out by the floating zone method, and photoluminescence (PL) and scintillation properties were measured. The PL spectra showed some emission lines which was derived from the 4f-4f transitions of Nd3+ ions. The scintillation spectra showed a broad emission band originating from some lattice defect and the emission lines due to the 4f–4f transitions of Nd3+ ions. The afterglow levels of Nd:La2Be2O5 were 192.3 (0.1 % Nd), 205.9 (0.5 % Nd), 228.2 (1.0 % Nd), and 315.4 (5.0 % Nd) ppm. The 1.0 % Nd:La2Be2O5 showed the highest intensity in the dose-rate response functions among the samples, and a lower detection limit was 0.003 Gy/h.

LArRI — A new setup for Liquid Argon Refractive index measurement

Liquid argon (LAr), widely used as the active target in neutrino and dark matter experiments, is a scintillator with a light yield of approximately 40 photons/keV. The scintillation spectrum is centered at 128 nm, and the attenuation length is of the order of meters, depending on the purity. The addition of small amounts of dopants allows for shifting the scintillation peak simplifying the light detection and opening the possibility to the development of imaging systems. There is no precise knowledge of the optical properties of LAr in the VUV range, but it could be exploited to improve the performances of liquid argon-based experiments, especially when the involved mass is in the ton scale. LArRI (Liquid Argon Refractive Index) aims to directly measure the refractive index of LAr in the VUV spectrum, using an interferometric technique. The refractive index is obtained by comparing two interference patterns, created in vacuum and liquid, acquired with cryogenic silicon photomultipliers. This work primarily presents the methodology, the preliminary tests, and the analysis strategy, which are intended to be applied to real data shortly.

Scintillator application of CsPbBr3 quantum dots-embedded SiO2 glasses

CsPbBr3 quantum dots-embedded SiO2 glasses were synthesized by the spark plasma sintering method as novel scintillators for γ-ray detectors. Their optical and scintillation properties were investigated to examine the scintillation performance. The X-ray diffraction patterns observed a halo peak of the SiO2 glass phase and diffraction peaks of CsPbBr3. An emission peak due to CsPbBr3 quantum dots was detected at around 515 nm in both photoluminescence (PL) and scintillation spectra. The PL and scintillation decay time curves included a component of nanosecond order, resulting from CsPbBr3 quantum dots. Under γ-ray irradiation from 137Cs, the light yield (LY) of the 0.2% CsPbBr3-embedded SiO2 glass was 150 photons MeV−1.

Probing the Interstellar Medium from Scintillation of the Swooshing Pulsar B0919+06

Radio observations of pulsars offer a potential method to probe the intricate microstructure in the turbulent interstellar medium. Here we report on a high-resolution dynamic spectral analysis of the “swooshing pulsar” B0919+06 observed with the Five-hundred-meter Aperture Spherical radio Telescope over multiple epochs and with the ultrawideband receiver on the Parkes radio telescope. For all observations, the dynamic scintillation spectra, two-dimensional autocovariance functions, and secondary spectra are presented. At 1250 MHz, the decorrelation bandwidth, diffraction timescale, and the drift rate are determined to be Δν d = 25.89 ± 7.55 MHz, Δτd=14.42±3.98 minutes, and dt/dν=0.07±0.14minutes MHz−1, respectively. The frequency dependencies of the scintillation parameters exhibit single power-law spectral behaviors, indicating that the electron density fluctuations in the interstellar medium approximately follow the Kolmogorov spectrum. The secondary spectra exhibit two distinct parabolic arcs with well-determined curvatures of 0.002 and 0.02 s3 for the outer and inner arcs, respectively. The locations of the scattering screens are approximately determined to be 157.3 and 726.0 pc, respectively, from the pulsar for isotropic scattering. The inner scintillation arc is present contemporaneously over a wide frequency range, indicating that the scintillation arc is a broadband phenomenon. The arc curvature scales with observing frequency as a power law with an index of −2.05 ± 0.05, which implies that the scattering screen spans a physical distance from 689.7 to 883.3 pc from the pulsar.

Scintillation and photostimulated-luminescence properties of Yb-doped SrCl2 transparent ceramics

We have investigated the photoluminescence (PL), scintillation, and photostimulated-luminescence (PSL) properties of Yb-doped SrCl2 transparent ceramics. The samples were prepared using the spark plasma sintering method. Emission peaks in the PL, scintillation, and PSL spectra were observed at 380 and 405 nm due to the spin-allowed and spin-forbidden 4f135d1–4f14 transitions of Yb2+, respectively. The PL quantum yield (QY) value elevated with increasing Yb concentration at 0.05%–1.0%, and the 1.0% Yb-doped SrCl2 transparent ceramic indicated the highest QY value. This concentration dependence was similar for the scintillation and PSL intensities.

Development of LiAlO2 nanoparticle-loaded plastic scintillators for neutron detection

We have developed LiAlO2 nanoparticle-loaded polystyrene-based plastic scintillators for neutron detection and evaluated the neutron detection properties. The size of LiAlO2 nanoparticles was ∼150 nm. The distribution of nanoparticles in the plastic scintillator was uniform in the horizontal direction but non-uniform in the vertical direction. The emission peak was observed around 420 nm in the scintillation spectra and is attributed to1,4-Bis[2-(5-phenyloxazolyl)] benzene (POPOP) included as an organic phosphor. The 10 wt% LiAlO2 nanoparticle-loaded plastic scintillators containing 22 wt% 2,5-Diphenyloxazole (DPO-POPOP (the molar ratio of 80:1) had the highest light yield of 1600 photons/neutron, which is significantly higher than that of a commercially available 10B-loaded plastic scintillators (BC-454) having a light yield of 800 photons/neutron.

Application of the spectral determination method to liquid scintillation spectra

ABSTRACT Previously we reported a simple algorithmic method of spectral determination method (SDM), which is based on the first principle that a γ-ray spectrum obtained for a sample is a linear superposition of individual spectra of the radioactive nuclides included in the sample and demonstrated that the method is valid for γ-ray determination. Here, we apply it to the spectra obtained by liquid scintillation counter (LSC). In LSC measurements quenching is generally observed, and we at first developed its correction method to standard spectra. The SDM code reported in the previous investigation is used to analyze the LSC spectra. Based on the analyses done by using the measured spectra, we concluded that the SDM method is valid in the LSC spectra similarly to the γ-ray spectra studied in the previous investigation.

Equatorial Ionospheric Scintillation Measurement in Advanced Land Observing Satellite (ALOS) Phased Array-Type L-Band Synthetic Aperture Radar (PALSAR) Observations

Amplitude stripes imposed by ionospheric scintillation have been frequently observed in many of the equatorial nighttime acquisitions of the Advanced Land Observing Satellite (ALOS) Phased Array-type L-band Synthetic Aperture Radar (PALSAR). This type of ionospheric artifact impedes PALSAR interferometric and polarimetric applications, and its formation cause, morphology, and negative influence have been deeply investigated. However, this artifact can provide an alternative opportunity in a positive way for probing and measuring ionosphere scintillation. In this paper, a methodology for measuring ionospheric scintillation parameters from PALSAR images with amplitude stripes is proposed. Firstly, sublook processing is beneficial for recovering the scattered stripes from a single-look complex image; the amplitude stripe pattern is extracted via band-rejection filtering in the frequency domain of the sublook image. Secondly, the amplitude spectrum density function (SDF) is estimated from the amplitude stripe pattern. Thirdly, a fitting scheme for measuring the scintillation strength and spectrum index is conducted between the estimated and theoretical long-wavelength SDFs. In addition, another key parameter, the scintillation index, can be directly measured from the amplitude stripe pattern or indirectly derived from the scintillation strength and spectrum index. The proposed methodology is fully demonstrated on two groups of PALSAR acquisitions in the presence of amplitude stripes. Self-validation is conducted by comparing the measured and derived scintillation index and by comparing the measurements of range lines and azimuth lines. Cross-validation is performed by comparing the PALSAR measurements with in situ Global Position System (GPS) measurements. The processing results demonstrate a powerful capability to robustly measure ionospheric scintillation parameters from space with high spatial resolution.

Observation of strong wavelength-shifting in the argon-tetrafluoromethane system

We report the scintillation spectra of Ar/CF4 mixtures in the range 210–800 nm, obtained under X-ray irradiation for various pressures (1–5 bar) and concentrations (0%–100%). Special care was taken to eliminate effects related to space charge and charge recombination, so that results can be extrapolated following conventional wisdom to those expected for minimum ionizing particles under the typical electric fields employed in gaseous instrumentation. Our study sheds light into the microscopic pathways leading to scintillation in this family of mixtures and reinvigorates the prospects of use in next-generation scintillation-based chambers.

Scintillation properties of (Ph4P)2ZnX4 (X = Cl, Br)

We fabricated (Ph4P)2ZnCl4 and (Ph4P)2ZnBr4 crystals (Ph4P: tetraphenylphosphonium) with zero-dimensional structures via solvent evaporation and evaluated their optical and scintillation properties. Fluorescence and phosphorescence peaks derived from Ph4P+ cations appeared at 345 and 510 nm, respectively, for both crystals, while an emission originating from self-trapped excitons was also detected for (Ph4P)2ZnBr4. In the scintillation spectra, both samples exhibited a phosphorescence peak, while a weak fluorescence peak was also observed for (Ph4P)2ZnCl4. In addition, the scintillation light yield (LY) was determined by pulse-height spectra with 1 μs shaping time. A pulse-height peak was observed from (Ph4P)2ZnCl4, and the scintillation LY was about 670 photons/5.5 MeV-α, which was higher than that of a ZnO single crystal.

Dosimetric properties of Tm2O3-doped Ca2BO3Cl

In this work, we prepared Ca2BO3Cl with various amounts (0.1%–1.0%) of Tm2O3 by conventional solid-state reaction and investigated the dosimeter properties. Scintillation peaks at 370, 455, 470, and 650 nm that were derived from the 4f→4f transition of Tm3+ appeared in the X-ray induced scintillation spectra, and the highest scintillation intensity was detected from the 0.5% Tm2O3-doped Ca2BO3Cl. Furthermore, the Tm2O3-doped Ca2BO3Cl exhibited a thermally-stimulated luminescence (TSL) with a main glow peak at 300 °C, and the fabricated Tm2O3-doped Ca2BO3Cl exhibited a linear response in the 0.1–1000 mGy range. In addition, the TSL spectra confirmed that a final luminescence process for the TSL was the 4f→4f transition of Tm3+. In addition to TSL, optically-stimulated luminescence that was attributable to the 4f→4f transition of Tm3+ was recorded under 520 nm light, and the lowest detectable limit was about 1 mGy.

Eu concentration dependence of photoluminescence and scintillation properties on Eu-doped Y3Al5O12 single crystals

(Eux,Y1-x)3Al5O12 (x = 0.005, 0.01, 0.05, 0.10, 0.15, and 0.20) single crystals were prepared by the floating-zone method. We investigated their photoluminescence (PL) and scintillation properties including PL excitation/emission contour spectra, PL quantum yields, PL decay times, X-ray-induced scintillation spectra, scintillation decay times, and pulse-height spectra under γ-ray irradiation from 137Cs (662 keV). The PL and scintillation spectra exhibited some emission lines at visible wavelength due to the 4f-4f transitions of Eu3+ ions, and the PL and scintillation decay times resulted several milliseconds. Among all the samples, (Eu0.1,Y0.9)3Al5O12 and (Eu0.15,Y0.85)3Al5O12 single crystals showed the highest PL quantum yield. On the other hand, (Eu0.01,Y0.99)3Al5O12 single crystal showed the highest light yield. The light yield of the sample was estimated to be 36,000 photons/MeV from the pulse height spectrum.

Evaluation of scintillation and dosimetric properties of undoped and Tb-doped Ba3Y(PO4)3 single crystals

Undoped and Tb-doped Ba3Y(PO4)3 single crystals were synthesized by the floating zone method. Photoluminescence (PL), scintillation, and dosimetric properties of the obtained single crystals were measured. The highest PL quantum yield value was obtained from the 15% Tb-doped crystal. In X-ray-induced scintillation spectra, the undoped crystal showed an emission peak due to self-trapped exciton at 400 nm. Tb-doped crystals showed emission peaks in the range of 375–620 nm, originated from 4f-4f transitions of Tb3+. In addition, the undoped and Tb-doped crystals showed luminescence peaks in similar locations to the scintillation spectra in thermally and optically stimulated luminescence (TSL and OSL). In TSL dose response functions, the 1% Tb-doped sample exhibited the highest TSL intensity, and the TSL signal was detectable from 0.01 mGy. In OSL dose response functions, the 5% Tb-doped sample exhibited the highest OSL intensity, and the OSL signal was observed from 0.1 mGy.

Photoluminescence, scintillation, and dosimetric properties of undoped and Tb-doped Ba3Gd(PO4)3 single crystals

Undoped and Tb-doped Ba3Gd(PO4)3 single crystals were synthesized by the floating zone method. Photoluminescence (PL), scintillation, and thermally stimulated luminescence (TSL) properties of the obtained single crystals were evaluated. The highest PL quantum yield value was obtained from the 5% Tb-doped single crystal. In X-ray-induced scintillation and TSL spectra, the undoped sample represented an emission peak originating from the 4f–4f transition of Gd3+ at 310 nm. The Tb-doped samples represented emission peaks originating from the 4f–4f transitions of Tb3+ and Gd3+ in the range of 310–620 nm. In TSL dose response functions, the 1% Tb-doped sample showed the highest TSL intensity, and the lower detection limit was 0.01 mGy.

Evaluation of photoluminescence and scintillation properties of Eu-doped YVO4 single crystals synthesized by optical floating zone method

0.1, 0.5, 1.0, and 5.0 % Eu-doped YVO4 single crystals were fabricated to assess photoluminescence (PL) and scintillation properties. The powder X-ray diffraction patterns of all the fabricated samples were the same as that of reference, and a single-phase structure of YVO4 was observed. The emission peaks owing to the 4f-4f transitions of Eu3+ ions were observed at 590, 605, 615, 620, and 695 nm in PL and scintillation spectra. Based on the pulse height spectra, Eu-doped samples had the light yield of 28,000 (0.1 % Eu), 33,000 (0.5 % Eu), 42,000 (1.0 % Eu), and 37,000 (5.0 % Eu) photons/MeV. In afterglow profiles, the afterglow level of 0.1, 0.5, 1.0, and 5.0 % Eu-doped samples was 58.1, 61.1, 49.1, and 35.6 ppm.

Scintillation properties of In-doped NaI transparent ceramics

In-doped NaI transparent ceramic scintillators were synthesized by the spark plasma sintering method, and In-doped NaI single crystal was grown by the Bridgman–Stockbarger method. The diffuse transmittance at the emission wavelength was ∼70% for the transparent ceramics and ∼90% for the single crystal. In the scintillation spectra under X-ray irradiation, emission peaks were observed at around 320, 460, and 510 nm in both of the transparent ceramic and single crystal samples. The peaks at 460 and 510 nm are due to 3P1 →1S0 transitions of In+. The decay time constants of the transparent ceramics and the single crystal were 1.8 μs. The X-ray induced afterglow level of the 0.1% In-doped NaI transparent ceramic and the single crystal was 170 and 777 ppm, respectively. In pulse height analysis, 662 keV photoabsorption peaks were clearly observed in all the samples when irradiated with 137Cs γ-rays. The light yield of the 0.1% In-doped NaI transparent ceramic was 19,000 ph/MeV, and that of the 0.1% In-doped NaI single crystal was 12,000 ph/MeV. The transparent ceramics showed better scintillation properties than the single crystal.

Vertically Well-Aligned ZnO Nanoscintillator Arrays with Improved Photoluminescence and Scintillation Properties.

ZnO nanoarrays were grown via a low-temperature hydrothermal method. Solutions, each with different additive combinations, were prepared and evaluated. The effects of the additives involved in the growth procedure, i.e., ammonium hydroxide and sodium citrate, were studied in terms of the morphological, optical and scintillation properties of the ZnO nanostructures. Measurement of the nanorod (NR) length, corresponding photoluminescence (PL) and scintillation spectra and their dependence on the additives present in the solution are discussed. ZnO NRs grown on a silica substrate, whose UV transmission was found to be better than glass, showed high-quality structural and optical properties. It was found that the addition of sodium citrate significantly reduced defects and correspondingly increased the intrinsic near-band-edge (NBE) UV emission intensity at ~380 nm. To obtain high-quality nanostructures, samples were annealed in a 10% H2 + 90% N2 atmosphere. The anneal in the forming gas atmosphere enhanced the emission of the UV peak by reducing defects in the nanostructure. NRs are highly tapered towards the end of the structure. The tapering process was monitored using time growth studies, and its effect on PL and reflectance spectra are discussed. A good alpha particle response was obtained for the grown ZnO NRs, confirming its potential to be used as an alpha particle scintillator. After optimizing the reaction parameters, it was concluded that when ammonium hydroxide and sodium citrate were used, vertically well-aligned and long ZnO nanoarrays with highly improved optical and scintillation properties were obtained.

Photoluminescence and scintillation properties of Tb-doped CaHfO3 single crystals

CaHfO3 was investigated as a promising candidate for a scintillator because of high density and large effective atomic number. Tb-doped CaHfO3 single crystals with various Tb concentrations were synthesized by the floating zone method, and the photoluminescence (PL) and scintillation properties were investigated. All the samples showed the highest PL emission intensity at 550 nm, and the origin of this emission was identified as 4f-4f transitions of Tb3+ by the obtained PL decay time constants. The X-ray-induced scintillation spectra showed several emission peaks in the range of 350–650 nm, which were attributed to the 4f-4f transitions of Tb3+. Based on the results of the pulse height spectra, the light yield of the 1.0% Tb-doped sample was calculated to be 12,000 photons/MeV, respectively.

Luminescence Characteristics of the MOCVD GaN Structures with Chemically Etched Surfaces.

Gallium nitride is a wide-direct-bandgap semiconductor suitable for the creation of modern optoelectronic devices and radiation tolerant detectors. However, formation of dislocations is inevitable in MOCVD GaN materials. Dislocations serve as accumulators of point defects within space charge regions covering cores of dislocations. Space charge regions also may act as local volumes of enhanced non-radiative recombination, deteriorating the photoluminescence efficiency. Surface etching has appeared to be an efficient means to increase the photoluminescence yield from MOCVD GaN materials. This work aimed to improve the scintillation characteristics of MOCVD GaN by a wet etching method. An additional blue photo-luminescence (B-PL) band peaking at 2.7-2.9 eV and related to dislocations was discovered. This B-PL band intensity appeared to be dependent on wet etching exposure. The intensity of the B-PL was considerably enhanced when recorded at rather low temperatures. This finding resembles PL thermal quenching of B-PL centers. The mechanisms of scintillation intensity and spectrum variations were examined by coordinating the complementary photo-ionization and PL spectroscopy techniques. Analysis of dislocation etch pits was additionally performed by scanning techniques, such as confocal and atomic force microscopy. It was proved that this blue luminescence band, which peaked at 2.7-2.9 eV, is related to point defects those decorate dislocation cores. It was shown that the intensity of this blue PL band was increased due to enhancement of light extraction efficiency, dependent on the surface area of either single etch-pit or total etched crystal surface.