Investigation of the Scintillation Properties of Domestic BaF2(La) Crystal

BaF₂(La) crystal has been grown with 1% mole of BaF₃ doped in BaF₂ and the scintillation properties of the new crystal have been investigated before and after a γ irradiation of ⁶⁰Co source.The radiation resistance of the domestic crystal can be up to a dose of 10⁶ rad.Comparing with a pure BaF₂ scintillator,it was found that the fast component of the BaF₂(La) scintillator was almost no change but its slow component was suppressed to a factor of 4.     

Spectral-kinetic characteristics of crystals and nanoceramics based on BaF<Subscript>2</Subscript> and BaF<Subscript>2</Subscript>: Ce

Optical characteristics of BaF₂ and BaF₂: Ce single crystals and nanoceramic materials prepared from these single crystals by uniaxial hot pressing have been studied. It has been shown that the introduction of Ce₃₊ ions into BaF₂ hardly affects the ultrafast (∼0.9 ns) luminescence component. The integrated luminescence intensity of the BaF₂: Ce nanoceramics is higher than that of the corresponding single crystal and considerably higher that the intensity of the undoped BaF₂ crystal. It has been demonstrated that the slow (several hundred nanoseconds) component of the luminescence decay of BaF₂: Ce is due to the energy transfer from excitons to Ce³⁺ ions.     

BaF2 Scintillator Coupling with a Low-pressure Multistep Avalanche Chamber

We studied the properties of a UV light sensitive low-pressure multistep avalanche chamber containing pure TMAE vapour.The gain of two chambers with different constructure at various temperatures is measured.With pure TMAE vapour at 40°C the gain of one chamber was 4×10⁵,the time resolution was 4.1ns.Coupling the chamber with a 2×2×2.4cm³ BaF₂ scintillator we successfully observed the signal of ¹³⁷Cs γ-ray of 0.661MeV.     

BaF2 Used for Particle Identification in Intermediate Energy Heavy Ion Raactions

A detector telescope consisting of a BaF₂ crystal and Si detectors is used to measure forwardly emitted products in ¹²C(46.7MeV/u)induced heavy ion reactions,both ΔE-E method and fast-slow correlation method are adopted in the particle identification.The response of BaF₂ to various incident ions has been studied.     

Electroluminescence from Multilayered Diamond/CeF3/SiO2 Films

We report a thin film electroluminescent device with a three-layer structure （diamond/CeF3/SiO2 films）, which has a luminance of 1.5 cd/m^2 at dc voltage 215 V. The electroluminescence spectrum at room temperature shows that the main peaks locate at 527 and 593nm, which are attributed to isolated emission centers of Ce^3＋ ions.     

Sol-gel法制备Er3+-Yb3+共掺杂Al2O3粉末光致发光特性

采用异丙醇铝[Al(OC₃H₇)₃]为前驱体,溶胶-凝胶(Sol-gel)法制备Er³⁺-Yb³⁺共掺杂Al₂O₃粉末.实验结果表明:900 ℃烧结的粉末为固溶Er³⁺、Yb³⁺的γ-(Al,Er,Yb)₂O₃相和少量θ-(Al,Er,Yb)₂O₃相的混合物.Er³⁺-Yb³⁺共掺杂Al₂O₃粉末具有中心波长为1.533 μm的光致发光(PL)特性.1 mol % Er³⁺和1 mol% Yb³⁺共掺杂的Al₂O₃粉末的PL强度较1 mol % Er³⁺掺杂提高2倍,半峰宽从53 nm增加到63 nm.随泵浦功率的提高,PL强度呈线性增加后渐呈饱和趋势.     

高温高压合成CeTbO3+δ的XPS研究

 经过高温高压合成的CeTbO_3+δ进行了XPS研究，发现在1.0 GPa下，Tb⁴⁺在~600 ℃开始转变成Tb³⁺，而Ce⁴⁺在~800 ℃开始向Ce³⁺转变。在1 000~1 200 ℃形成单相萤石结构化合物CeTbO_3+δ的Ce是以Ce³⁺、Ce⁴⁺混合价形式存在，Tb全部变成Tb³⁺。实验表明，用Ce_3d谱上~888 eV峰的峰位及其与882 eV峰的相对强度变化可以定性判断化合物中是否含有Ce³⁺。研究了高温高压合成的CeTbO_3+δ的稳定性随时间的变化问题。     

Cooperative Quantum Cutting of Nano-Crystalline BaF2：Tb^3＋, Yb^3＋ in Oxyfluoride Glass Ceramics

We report on cooperative quantum cutting in Tb^3＋- Yb^3＋ codoped glass ceramics. Precipitation of BaF2 nanocrystals is confirmed by XRD and HRTEM analysis. Near-infrared emission due to transition of Yb^3＋ ions under 485 nm excitation indicates cooperative energy transfer from Tb^3＋ to Yb^3＋. The quantum efficiency of this process reaches 145%. The realization of quantum cutting in glass ceramics may have promising applications in solar cells.     

STUDY ON RADIATION DAMAGE OF CHINESE-MADE HIGH-Z SCINTILLATION CRYSTALS

Radiation damage effects of several Chinese-made high-Z scintillation crystals have been studied on a ⁶⁰Co irradiation unit of 100KCi Results on small size BGO crystals irradiated by 60Co γ rays with various doses from 5×10³ to 7.5×10⁵rad are presented.The decrease in scintillation light output depends non-linearly on the dose applied and saturation effects above 5×10⁴rad have been observed.The spontaneous recovery of the light output can be described by the sum of at least three exponential functions.The radiation damage effects of small size BaF₂,CsI(Tl) and ZnWO₄ crystals at 5×10⁵rad were also investigated.Serious damage to BaF₂ has been found.Preliminary analyses indicate that this may be attributed to the inclusion of certain critical elements in the crystal.CsI(T1) after irradiation does not exhibit strong afterglow of noticeable coloration as were reported in the literature.     

Slow components of the emission decay in fluoride crystals doped with Ce3+

Spatially separated defects created by photons with energies 6–8 eV in alkali-earth fluoride crystals doped with cerium are investigated with the help of thermoluminescence. Measuring the spectra of creation of V_k and H peaks of thermostimulated luminescence inBaF ₂:Ce³⁺. we demonstrate that photons with energies higher than 6eV induce H centers (self-trapped holes captured by interstitialF ions), whereas the formation of self-trapped holes begins on exposure to photons with energies greater than 7 eV. The influence of photoionization on theCe ³⁺ luminescence inBaF ₂, SrF₂, CaF₂, andCeF ₃ crystals is investigated in the range of photon energies 4–8 eV. An exponentialCe ³⁺-emisson decay was observed for excitation energy lying in the range 4–6 eV. Slow and fast decay components were observed under excitation by photons with energies higher than 6 eV. We believe that the slow and fast components are due to the tunnel recombination of trapped electrons with hole centers. A. P. Vinogradov Institute of Geochemistry of the Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 43–49, March, 2000.     

Experimental Study on 22Na(p,γ)23Mg Reaction

The reaction of ²²Na(p,γ)²³Mg has been investigated at the Radioactive Ion Beam Line in Lanzhou(RIBLL) using a radioactive beam ²³Al. The β⁺ delayed proton decay spectrum has been measured with the TOF-ΔE method and zero degree detectors. The half life of ²³Al is determined to be T_1/2=(476±45)ms by using a time scaler combined with the precision pulse generator,which is consistent with the other group's result of (470±30)ms. The known β⁺ delayed protons at E_r=0.216,0.278,0.438,0.479MeV have also observed in the experiment. The resonance strength of isospin analog state (IAS) is calculated. The resonance intensity of IAS is (11.4±6.0)meV. A new energy level of β⁺ delayed proton decay has been identified at E_x=8.916MeV,and their relative intensity also been obtained.     

A STRUCTURE MODEL OF STRATONS AND LEPTONS

A subquark model is proposed. According to this model, stratons and leptons are consisted of rishons T and V, which are multiplets of group SU_H(3)×SU_C(3)×SU_G(2)×SU(2)×U(1). Three generations of both stratons and leptons are obtained naturally. In this model, proton decay modes are μ^－e⁺e⁺ or e^－μ⁺μ⁺.     

Observation of Heavy Cluster Emission From Radioactive 230U Nuclei

230Pa was produced with the reaction ²³²TH (p, 3n)230Pa in the irradiation powder targets of ThO₂ with 35 MeV Proton beam. Sources of ²³⁰Pa -²³⁰U were prepared by radiochemical method. Using solid-state track registration detectors, two events of ²³⁰U decay with heavy cluster emission have been observed. The preliminary branching ratio to decay comes out to be B=λ_Ne/λ_α=(1.3±1.8)×10^－14.     

Charge Transfer Luminescence in Ce-Doped Fluorides

New emission bands were found in Ce^3? doped SrF₂ and BaF₂ crystals under excitation into the charge transfer region. The bands at 4.85 eV in BaF₂ and 4.35 eV SrF₂ were found in all crystals with Ce-concentration from 0.001 to 1 mol.%, most prominent in 0.01% samples. Decay of luminescence was simple exponential in BaF₂, decay time decreased from 1.3 ms at 65 K to 0.41 μs at 523 K. The decay curve in SrF₂ shows t^?0.3 dependence at room temperature. All experimental results were naturally explained by assumption that new emission belongs to radiative charge transfer recombination in Ce^2?—F_i^o pairs with different distances between them.     

Band Gap Energies and Refractive Indices of Epitaxial Pb1-xSrxTe Thin Films

Pb1-x Srx Te thin films with different strontium （St） compositions axe grown on BaF2 （111） substrates by molecular beam epitaxy （MBE）. Using high resolution x-ray diffraction （HPLXRD）, we obtain Pb1-xSrxTe lattice constants, which vary in the range 6.462-6.492 A. According to the Vegard law and HRXRD data, Sr compositions in Pb1-xSrxTe thin films range from 0.0-8.0%. The Pb1-xSrxTe refractive index dispersions are attained from infrared transmission spectrum characterized by Fourier transform infrared （FTIR） transmission spectroscopy. It is found that refractive index decreases while Sr content increases in Pb1-xSrx Te. We also simulate the Pb1-xSrxTe transmission spectra theoretically to obtain the optical band gap energies which range between 0.320 e V and 0.449 e V. The simulated results are in good agreement with the FTIR data. Finally, we determine the relation between Pb1-xSrx Te band gap energies and Sr compositions （Eg = 0.320＋0.510x-0.930x^2 ＋184x^3 （eV））.     

Experimental Measurements for the QEC-Value of 183Os-Decay

Activities of ¹⁸³Os were produced by 39MeV α particles bombarding on a natural tungsten target.β⁺ spectrum with coincidence gate set on the strongest 382keV γ-rays of ¹⁸³Os decay was measured.The endpoint energy of the β⁺ spectrum was determined and the Q_EC value of ¹⁸³Os decay was extracted to be 2.24±0.10MeV which is in good agreement with the predicted value 2.30±0.10MeV on the basis of mass systematics.     

About Three-Body Exit Channel in the Reaction 12C+16O at EL(16O)=56MeV

Three-body exit channel in the reaction ¹²C+¹⁶O at 56MeV has been studied by using measurement of the coincidence between the two changed particles.The projected spectra of the coinsidence between the two α-particles shows that the channel α+²⁴Mg is the main intermediate process of three-body exit channel α₁+α₂+²⁰Ne in the reaction ¹²C+¹⁶O at 56MeV.The analysis of theoretical calculation showed that the sum of sequential decay and statistical break-up fit the experimental spectra satisfactorily.     

First Experimental Determination of Half-Life for New Nuclide 65Se

By using experimental data obtained from the measurement of beta-delayed proton decay of ⁶⁵Se produced in ⁴⁰Ca(²⁸Si,3n)reaction,the absolute detection efficiency of particle telescope for rotating radioactive source was imitatively calcu-lated.The half-life of ⁶⁵Se was thus accurately determined to be 9.6_-4.1^+5.3 ms.The β-delayed proton energy of ⁶⁵Se was 3.70±0.08MeV.The partial decay scheme of ⁶⁵Se β-delayed proton decay was revised and proposed.     

Structure Analysis of the l/η(1440)

By an amplitudes analysis of the KKπ system in the J/ψ radiative decay to the K⁺K^－π^O and the K⁰_SK^±π⁺ final states, we find that there is one 0^－+ resonance (M=1467±3MeV,Γ=89±6MeV) and two 1⁺⁺ resonances (M=1435±3MeV,Γ=59±5MeV and M=1497±2MeV,Γ=44±7MeV), Which are consistent with the η(1440), the f₁(1420), and the f₁(1510).     

The fluorescence and thermoluminescence characteristics of α-Al2O3:C ceramics

This paper reports that polycrystalline α-Al₂O₃:C ceramics are fabricated by conventional ceramics process. The excitation, emission spectra, thermoluminescence (TL) and optical stimulated luminescence (OSL) of α-Al₂O₃:C polycrystalline ceramics are investigated. There exists 410nm maximum emission peak which is caused by recombination of an electron with F⁺ centre to produce an excited F centre. The samples show three clear TL glow peaks at 405, 493 and 610K. The attenuation constant of exponentially decaying fast component (τ₁) and slow component(τ₂) of OSL curve are 8.43s and 41.73s, respectively. Those fluorescence and thermoluminescence characteristics are similar with α-Al₂O₃:C crystal.