Pulse-shape analysis of Cs2LiYCl6:Ce scintillator for neutron and gamma-ray discrimination

Cs₂LiYCl₆:Ce (CLYC) is one of the most promising new scintillators for detecting both neutrons and gamma-rays. Its neutron and gamma-ray discrimination capability using pulse-shape analysis has drawn much attention, and there is significant interest in its use in field applications. For such applications, compact and low-power readout electronics capable of exploiting the pulse-shape discrimination (PSD) capabilities of CLYC will be essential. A readout system centered around a PSD-capable application specific integrated circuit (ASIC) that is well-suited for use with CLYC has been characterized, tested, and validated. As part of this study, automated analysis of CLYC data collected with a fast waveform digitizer extracted optimized charge integration windows for PSD. Additionally, several different CLYC samples were studied in order to gain understanding of the dependance of pulse shapes on parameters such as crystal size, ⁶Li enrichment level, crystal packaging, and choice of PMT. Extremely good PSD performance was obtained from CLYC scintillator and the ASIC-based readout system.     

Study on structural phase transitions and relaxation processes of Cs2Co(SO4)2·6H2O and Cs2Zn(SO4)2·6H2O crystals

The structural phase transitions and relaxation processes of Cs₂Co(SO₄)₂·6H₂O and Cs₂Zn(SO₄)₂·6H₂O single crystals were investigated, with the phase transitions of both crystals being determined from NMR data. The spin–lattice relaxation time, T₁, of the ¹³³Cs nucleus in two crystals undergoes a significant change near the phase transition temperature, T_C, and these changes coincide with the changes in the splitting of the ¹³³Cs resonance lines. The variations in the temperature dependence for the splitting of the ¹³³Cs resonance lines and T₁ near T_C are related to changes in the symmetry of surrounding Cs⁺. In addition, the ¹³³Cs T₁ of Cs₂Co(SO₄)₂·6H₂O, which contains paramagnetic ions, was found to be shorter than that of Cs₂Zn(SO₄)₂·6H₂O. This relaxation time is inversely proportional to the square of the magnetic moment of the paramagnetic ions. The differences between the ¹³³Cs T₁ of these compounds are probably due to the differences between the electronic structures of their metal ions.     

Scintillation properties of Nd, Tm, and Er doped LuF3 scintillators in the vacuum ultra violet region

In order to develop novel vacuum ultra violet (VUV) emitting scintillators, we grew Nd 0.5%, Tm 0.5%, and Er 0.5% doped LuF₃ scintillators by the μ-pulling down method, because LuF₃ has a very wide band gap and Nd³⁺, Tm³⁺, and Er³⁺ luminescence centers show fast and intense 5d-4f emission in VUV region. Transmittance and X-ray induced radioluminescence were studied in these three samples using our original spectrometer made by Bunkou-Keiki company. In the VUV region, transmittance of 20-60% was achieved for all the samples. The emission peaks appeared at approximately 180, 165, and 164 nm for Nd³⁺, Tm³⁺, and Er³⁺ doped LuF₃, respectively. Using PMT R8778 (Hamamatsu), we measured their light yields under ²⁴¹Am α-ray excitation. Compared with Nd:LaF₃ scintillator, which has 33 photoelectrons/5.5 MeV α, Nd:LuF₃ and Tm:LuF₃ showed 900±90 and 170±20 ph/5.5 MeV-α, respectively. Only for the Nd doped one, we can detect ¹³⁷Cs 662 keV γ-ray photoabsorption peak and the light yield of 1200±120 ph/MeV was measured. We also investigated their decay time profiles by picosecond pulse X-ray equipped streak camera, and the main decay component of Nd:LuF₃ turned out to be 7.63 ns.     

Crystal growth and scintillation properties of Ce and Eu doped LiSrAlF6

Ce and Eu doped LiSrAlF₆ (LiSAF) single crystals for the neutron detection with different dopant concentrations were grown by the micro-pulling-down method (μ-PD). In Ce:LiSAF, intense emission peaks due to Ce³⁺ 5d-4f transitions were observed at approximately 315 and 335 nm in photo- and α-ray induced radio-luminescence spectra. In case of Eu:LiSAFs, an intense emission peak at 375 nm due to Eu²⁺ 5d-4f transition was observed in the radio-luminescence spectra. The pulse height spectra and decay time profiles were measured under ²⁵²Cf neutron irradiation to examine the neutron response. The Ce 3% and Eu 2% doped LiSAF showed the highest light yield of 2860 ph/n with 19 ns main decay time component and 24,000 ph/n with 1610 ns.     

Synthesis of ultra-long single crystalline CuV2O6 nanobelts

Ultra-long single crystalline CuV₂O₆ nanobelts have been successfully synthesized via a facile homogeneous reaction between peroxovanadic acid and cupric acetate. The reaction parameters, such as reaction time, and with or without H₂O₂, have profound influences on the crystal structures and morphologies of the resulting products. The time-dependent experiments reveal that the formation of ultra-long CuV₂O₆ nanobelts is related to the disassembly of urchin-like Cu₃(OH)₂V₂O₇·2H₂O nanostructures composed of radially aligned nanobelts, and the growth of CuV₂O₆ along the direction of [010]. Without the addition of H₂O₂ aqueous solution, wide and short CuV₂O₆ nanobelts coexist with some irregular particles and microrods in the products.     

Scintillation characteristics of Cs2LiCeBr6 crystal

This work investigates the scintillation properties of Cs₂LiCeBr₆ crystal as a new material for radiation detection. This scintillation material is grown by the vertical Bridgman method. Under X-ray excitation the sample crystal shows a broad cerium based emission band between 390 and 450 nm wavelength range. Energy resolution for 662 keV γ-rays is measured to be 7.4% (FWHM). At room temperature Cs₂LiCeBr₆ crystal exhibits three exponential decay time components. The fast and major component of scintillation time profile of Cs₂LiCeBr₆ emission decays with a 86 ns time constant. Absolute light yield for the sample crystal is estimated to be 27,000 and 29,000 photons/MeV using APD and photomultiplier tube, respectively. The sample crystal shows good proportionality of 5% in the measured energy range from 31 to 1333 keV. This study showed that this new scintillation crystal can be a good candidate for radiation detection and medical imaging. The sample crystal is highly hygroscopic.     

Preparation and characterization of NaSm9(SiO4)6O2 powders with infrared absorptive properties

NaSm₉(SiO₄)₆O₂ powders were synthesized by mild hydrothermal method at 180 °C for 24 h. The infrared optical properties and structure of the obtained powders were characterized. There existed two narrow and sharp absorptive bands near 943 cm^− 1 (10.6 μm). The band at 938 cm^− 1 was assigned to the stretching vibrations of SiOSm groups connecting to Q¹ species and the band at 989 cm^− 1 was attributed to the stretching vibrations of SiOSm groups linking with Q⁰ species. The reflectivity was lower than 1% from 900 to 1200 nm and reached the minimum of 0.46% at 1073 nm. The prepared powders exhibit potential to act as a new kind of absorptive material for the infrared light of 10.6 μm and 1.06 μm.     

Luminescence properties of Sn2P2Se6 crystals

A large family of Sn_2yPb_2(1−y)P₂S_6xSe_6(1−x) semiconductor-ferroelectric crystals were obtained by the Bridgman technique. The photoluminescence properties of the Sn_2yPb_2(1−y)P₂S_6xSe_6(1−x) family crystals strongly depend on their chemical composition, excitation energy and temperature. The influence of the Pb → Sn and S → Se isovalent substitutions on the luminescence properties of a crystal with the Sn₂P₂Se₆ basic composition was investigated. A broad emission band observed in the Sn₂P₂Se₆ crystal with a maximum roughly at 600 nm (at T = 8.6 K) was assigned to a band-to-band electron-hole recombination, whereas broad emission bands, peaked near 785 nm (at T = 8.6 K) and 1025 nm (at T = 44 K) were assigned to an electron-hole recombination from defect levels localised within the bandgap. Possible types of recombination defect centres and specific mechanisms of luminescence in the Sn₂P₂Se₆ semiconductor-ferroelectric crystals were considered and discussed on the basis of the obtained results and the referenced data.     

Photoelectrochemical properties of thin Bi2WO6 films

Thin Bi₂WO₆ film prepared from an amorphous heteronuclear complex via dip-coating method is investigated as a visible light-driven photoelectrode material. Photoelectrochemical properties of the resultant film are investigated on the basis of linear sweep voltammetry and current-time curves, and conduction and valence band edges of the film electrode are determined from the photocurrent voltage response. Anodic photocurrent associated with the oxidation of water is obtained under visible light irradiation. Furthermore, the film as a photoanode can degrade rhodamine B (RhB) and methylene blue (MB) in aqueous solution under visible light irradiation slowly. The application of bias potential further improves the photodegradation efficiency of RhB and MB. Based on the analytic result of current-time curve, the stability of the film electrode is confirmed.     

Scintillation properties of Ce-doped LuLiF4 and LuScBO3

The crystals of 1 mol% Ce-doped LuLiF₄ (Ce:LLF) grown by the micro-pulling down (μ-PD) method and 1 mol% Ce-doped LuScBO₃ (Ce:LSBO) grown by the conventional Czochralski (Cz) method were examined for their scintillation properties. Ce:LLF and Ce:LSBO demonstrated ∼80% transparency at wavelengths longer than 300 and 400 nm, respectively. When excited by ²⁴¹Am α-ray to obtain radioactive luminescence spectra, Ce³⁺ 5d-4f emission peaks were detected at around 320 nm for Ce:LLF and at around 380 nm for Ce:LSBO. In Ce:LSBO, the host luminescence was also observed at 260 nm. By recording pulse height spectra under γ-ray irradiation, the absolute light yield of Ce:LLF and Ce:LSBO was measured to be 3600±400 and 4200±400 ph/MeV, respectively. Decay time kinetics was also investigated using a pulse X-ray equipped streak camera system. The main component of Ce:LLF was ∼320 ns and that of Ce:LSBO was ∼31 ns. In addition, the light yield non-proportionality and energy resolution against the γ-ray energy were evaluated.     

Scintillation and optical properties of Pb-doped YCa4O(BO3)3 crystals

This communication reports optical properties and radiation responses of Pb²⁺ 0.5 and 1.0 mol%-doped YCa₄O(BO₃)₃ (YCOB) single crystals grown by the micro-pulling-down (μ-PD) method for neutron scintillator applications. The crystals had no impurity phases according to the results of X-ray powder diffraction. These Pb²⁺-doped crystals demonstrated blue-light luminescence at 330 nm because of Pb²⁺¹S₀-³P_0,1 transition in the photoluminescence spectra. The main emission decay component was determined to be about 250-260 ns under 260 nm excitation wavelength. When irradiated by a ²⁵²Cf source, the relative light yield of 0.5% Pb²⁺-doped crystal was about 300 ph/n that was determined using the light yield of a reference Li-glass scintillator.     

Growth and spectral properties of Cr:KAl(MoO4)2 crystal

The Cr³⁺:KAl(MoO₄)₂ single crystal was grown by top seeding solution growth method (TSSG). Based on the absorption and emission spectra, the crystal field strength Dq, the Racah parameters B and C, the effective phonon energy ?ω and the Huang-Rhys factor S were calculated: Dq = 1494.8 cm^− 1, B = 585.5 cm^− 1 and C = 3049 cm^− 1, ?ω = 373.8 cm^− 1 and the Huang-Rhys factor S = 3.74, respectively. The value Dq/B = 2.55 indicates that Cr³⁺ ion occupies the strong crystal field site in KAl(MoO₄)₂ crystal. A comparison of crystal field parameters for Cr³⁺:KAl(MoO₄)₂ with other Cr³⁺-doped crystals was presented. The results of spectral measurement show that Cr³⁺:KAl(MoO₄)₂ may be a potential candidate for broadband laser applications.     

Synthesis of the intermetallic clathrate Na2Ba6Si46 by oxidation of Na2BaSi4 with HCl

A new preparation route to the intermetallic clathrate-I compound Na₂Ba₆Si₄₆ is introduced, which allows one to make large amounts of product with standard laboratory equipment. The precursor Na₂BaSi₄ is oxidized with gaseous HCl at 673 K to Na₂Ba₆Si₄₆, NaCl and BaCl₂. Full-profile refinement of the crystal structure from the X-ray powder diffraction data revealed a composition close to Na₂Ba₆Si₄₆ (Na_1.94(1)Ba_6.06(1)Si₄₆, space group , a=10.281(1) Å). Differential scanning calorimetry showed an exothermic effect at 874 K, indicating that Na₂Ba₆Si₄₆ is metastable. The product was additionally characterized by scanning electron microscopy. The electronic structure of Na₂Ba₆Si₄₆ was investigated by a first-principles, all-electron full-potential method, predicting metallic conductivity. Na₂Ba₆Si₄₆ obtained by oxidation with HCl shows Pauli paramagnetism; no bulk superconductivity was found down to 1.8 K in a magnetic field of 20 Oe.     

Formation of rod-crystals on CuInSe2 thin films by SILAR method using CH3-(CH2)11-C6H4-SO3Na surfactant

The formation of rod-crystals was observed on CuInSe₂ thin films prepared by successive ionic layer adsorption and reaction (SILAR) method using sodium dodecylbenzene sulfonate (SDBS) as directing agent. Rod-crystals appeared on the surface of CuInSe₂ thin film when adding SDBS into cationic precursor solution. FESEM, EDS, XRD and HRTEM were used to characterize the rod-crystals. The length of rod-crystals has a proportional relationship with SDBS amounts in the given scope of 0.001-0.01 mol/L. The stoichiometry of rod was close to 1:1:2 of CuInSe₂, and rod growth of partially preferential orientation along [112] was observed. The growth of rod could be explained by steric hindrance effects of SDBS adsorbed on the inorganic deposit surface.     

Synthesis and characterization of novel nanostructured fishbone-like Cu(OH)2 and CuO from Cu4SO4(OH)6

The Cu₄SO₄(OH)₆ was synthesized by a simple hydrothermal reaction with a yield of ~ 90%. Using Cu₄SO₄(OH)₆ as the starting material, novel fishbone-like Cu(OH)₂ was produced by a direct reaction of Cu₄SO₄(OH)₆ with NaOH solution. The Cu(OH)₂ consists of many needle-like nanorods parallel to each other and perpendicular to the direction of backbone, forming fishbone-like structure. Using the fishbone-like Cu(OH)₂ as the sacrificial precursor, CuO with similar size and morphology was obtained through a simple heat treatment. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, X-ray photoelectron spectroscopy, BET nitrogen adsorption, and UV-Vis absorption spectroscopy were employed to characterize the as-prepared samples. The conversion of the Cu₄SO₄(OH)₆ to the fishbone-like Cu(OH)₂ was visualized by time-dependent SEM images. A mechanism was also proposed based on the observed results.     

Growth and spectral properties of Er:NaGd(WO4)2 crystal

A high optical quality Er³⁺-doped NaGd(WO₄)₂ single crystal with dimensions of ∅18 × 50 mm³ has been grown using the Czochralski method. The structure of the grown crystal was proved by X-ray powder diffraction. The accurate concentration of Er³⁺ ion in the crystal was measured. The absorption spectra, fluorescence spectra and fluorescence lifetime of the crystal were measured at room temperature. Green up-conversion luminescence has been observed when the crystal is excited at 965 nm.     

Magnetic properties of β-FeSi2 single crystals

We investigated temperature and magnetic field dependences of the magnetization of β-FeSi₂ single crystals in the temperature range of 5-300 K in magnetic fields up to 15 kOe. The temperature dependence of the magnetic susceptibility of the Cr- and Ni-doped sample can be explained by temperature-dependent contributions due to paramagnetic centres and due to the carriers excited thermally in the extrinsic conductivity region. The values of the paramagnetic Curie temperature as well as activation energy of the donor and acceptor levels are estimated.     

Synthesis of hexagonal prisms and hexagonal plates of Na2SiF6 microcrystals

Hexagonal Na₂SiF₆ prisms and hexagonal or dodecagonal Na₂SiF₆ plates were prepared using Na₂CO₃, SiO₂, and HF under microwave irradiation for the large-scale production of ice-analog materials. The morphology of the Na₂SiF₆ crystals changed from long thin hexagonal prisms to flat hexagonal or dodecagonal plates with pyramidal faces as the Na₂CO₃ concentration was increased. X-ray diffraction studies confirmed that the axes of the hexagonal Na₂SiF₆ prisms were aligned along the c axis. The microwave irradiation time played an important role in controlling the morphology and aspect ratio of the Na₂SiF₆ microcrystals. The mechanisms of formation of the various Na₂SiF₆ microcrystalline morphologies are discussed.     

Resistive upper critical field of single crystals of Tl2Ba2CuO6

We have measured the resistive upper critical field of overdoped single crystals of Tl₂Ba₂CuO₆ from the zero-field transition temperatureT _c (approximately 20 K) to temperatures as low as 12 mK, corresponding to less than 0.001T _c. In sharp contrast to the predictions of standard theories of superconductivity, the critical field is found to rise steeply with positive curvature as the temperature is reduced, and no sign of saturation is observed down to the lowest temperatures reached.     

Thermal properties and infrared spectra analysis of monoclinic RbGd(WO4)2 single crystals

Monoclinic rubidium gadolinium bis(tungstate) single crystals, RbGd(WO₄)₂ (RGW), have been grown by the spontaneous nucleation from high-temperature solutions. The thermal properties were firstly studied by measuring DSC, TG and specific heat. The melting point was determined to be 1089 °C. The measured specific heat ranges from 0.141 J g^− 1 K^− 1 to 0.564 J g^− 1 K^− 1 in the temperature range from 60 °C to 700 °C, a value that is slightly smaller than that of KGd(WO₄)₂. An infrared spectrum of the crystal was recorded in the frequency range of 50 to 1000 cm^− 1 and all vibration frequency peaks were assigned.