Thermoluminescence response of K2YF5:Tb3+ crystals to photon radiation fields

This investigation has been performed to test the feasibility of using K2YF5:Tb3+ crystals as thermoluminescence dosemeters (TLD). K2YF5 single crystals doped with 0.2, 10.0 and 50.0 at.% of trivalent optically active Tb3+ ions as well as K2TbF5 and undoped K2YF5 crystals have been synthesized under hydrothermal conditions. Polished crystal platelets with thickness of about 1 mm have been irradiated with X and gamma rays in order to study thermoluminescent (TL) sensitivity as well as dose and energy response in terms of the Tb3+ concentration in K2YF5. Within this concentration series, K2YF5 crystals doped with 10.0 at.% Tb3+ have been found to have maximum TL response due to a broad asymmetric TL glow peak at 269 degrees C with good linearity of dose response and reproducibility of dose measurements. After deconvolution, the main dosimetric peak has been revealed to be composed of two individual peaks, both with linear TL response behaviour, centered at 210 and 269 degrees C. As it has been proved, the linear TL signal coefficient for K2Y0.9Tb0.1F5 is almost 10 times greater than that for commercial TLD-100 (LiF:Mg,Ti), irradiated with a 137Cs gamma radiation source at the same conditions. The reported results indicate that K2YF5 crystals doped with Tb3+ have potential as promising materials for radiation dosemeters.     

光刺激发光技术鉴别辐照茶叶的研究

利用某些晶体能束缚高能载体的特点,建立一种可以快速鉴别经过辐照处理的茶叶的方法。该方法系采用特定光源刺激受过辐照处理的样品,使其包含的高能电子受激发而释放特定光子,被仪器所检测。研究结果表明,该方法可以有效的鉴别经过辐照处理的茶叶样品。     

Relaxation of optical excitations in crystals of the Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system with radiation defects

The photoluminescence and short-time persistence (afterglow) kinetics in pure and doped Y₂O₃-Al₂O₃ crystals excited with UV laser pulses (12 ns, 337 nm) were studied using samples irradiated with gamma quanta from a ⁶⁰Co source to a dose from 10⁴ to 10⁷ Gy. The relaxation time of the samples studied increases, with decreasing symmetry of the crystal lattice, in the following order: garnet—orthoaluminate—ruby—yttria. The afterglow duration and intensity significantly decrease in gamma-irradiated crystals, which is explained by the predominant recombination of close electron-hole pairs. Garnet-neodymium crystals are characterized by high radiation stability and fast relaxation kinetics.     

Radiation-thermal effects in single crystal corundum

Radiation-thermal effects were studied in corundum single crystals exposed to an ionizing radiation. The laws of variation of the electrical properties of a target material under the action of these factors were established. In particular, it is established that the dose dependence of the electric conductivity of irradiated samples is described by a curve with extremum. The radiation-induced phenomena observed are explained within the framework of existing models. The temperature dependence of the dielectric loss tangent of irradiated samples changes in a complicated manner (in particular, a maximum appears in this curve). There are two temperature regions in which the loss tangent exhibits special features. The activation energies have been determined and a hypothesis about the nature of the observed dielectric absorption is formulated.     

Irradiation effect on the electrical properties of corundum and quartz single crystals

The radiation effects in corundum and quartz crystals have been assessed at temperatures from 25 to 450°C and gamma doses from 10⁴ to 10⁹ rad. The radiation effects on the conductivity and dielectric losses of the crystals have been shown to be nonlinear, with extrema and inflections. The conductivity of corundum is characterized by three-step kinetics, with pronounced carrier generation in the range 100–200°C and restoration of parameters at 400°C in crystals irradiated to high doses. Both corundum and quartz crystals have extrema tanδ(t) in at different gamma doses. The peaks (200–250 and 50–150°C) grow with increasing frequency, without shifting to higher temperatures. The peaks seem to be due to different mechanisms of dielectric losses. The dose dependences of tanδ and σ have been compared up to 5 × 10⁹ rad and have been shown to correlate with one another. The extrema have been interpreted in terms of the Vul model. We have analyzed the possible origins of the loss maxima and have evaluated the activation energies for ionic polarization and conduction in the materials studied. We assume that the dielectric losses in the irradiated crystals are determined by conduction and polarization.     

Evaluation of the dosimetric response for CaSO4:Dy at low temperature

Homemade solid state CaSO4:Dy detectors were tested to evaluate their response to gamma radiation at liquid nitrogen temperature (77 K). The dosemeters were irradiated with doses between 12 and 1071 Gy. For this study these dosemeters were exposed to gamma rays with a dose rate of 1.19 Gy.min(-1). The analysis for these crystals was made by thermoluminiscence. The dose response at liquid nitrogen temperature was linear in the dose range studied and it is about 20% lower with respect to the response at room temperature. The response is reproducible with the same geometric set-up.     

Optical damage of the surface of sodium and potassium chlorides by femtosecond laser pulses

Optical damage thresholds for the surface of sodium and potassium chloride crystals irradiated by 80-fs laser pulses have been determined. P-polarized terawatt radiation of a chromium-forsterite laser operating at a wavelength of 1240 nm was incident on a sample surface at an angle of 35°. The optical damage of the crystal surface was observed when the electric field strength reached a critical level of 76 MV/cm for NaCl and 64 MV/cm for KCl.     

Radiation resistance diagnostics of wide-gap optical materials

Novel approach in the detection of radiation damage created by ion beams in optical materials was demonstrated. Protons of the energy of 100 keV and fluence of 10¹⁷ cm⁻² create sufficient amount of crystal lattice defects in the thin surface layer for testing of optical materials needed for future fusion reactors. These structural defects can be detected and analysed using the spectra of cathodoluminescence excited in the irradiated layer by an electron beam with adjustable energy. The method was verified by the enhanced intensity of F-type luminescence that reflects the creation of radiation-induced oxygen vacancies in MgO and Al₂O₃ crystals. Low radiation resistance of nominally pure (Lu_1-xGd_x)₂SiO₅ crystals was demonstrated by almost total suppression of intrinsic luminescence after the same irradiation.     

Transformation of the excitation energy in aniondefective corundum

Some regular features of the excitation energy transformation in anion-defective crystals of alpha-Al2O3 were analysed by the sub-nanosecond spectroscopic method. The samples were excited using synchrotron radiation and high-density pulsed electron beams. It was shown that much of the energy of the ionising radiation absorbed by the crystals was liberated as the luminescence of F- and F-centres immediately at the moment of irradiation. Luminescence of F+-centres dominated in the nanosecond range, while luminescence of F-centres prevailed in the millisecond range. The excitation energy transformation processes and their kinetics were governed by the temperature, the concentration ratio of intrinsic defects in alpha-Al2O3 crystals, and the excitation density.     

High resolution X-ray diffraction studies on unirradiated and irradiated strontium hexaferrite crystals

High-resolution X-ray diffraction technique, employing a three-crystal monochromator?Ccollimator combination is used to study the irradiation induced defects in flux grown Sr-hexaferrite crystals irradiated with 50?MeV Li³⁺ ion beams at room temperature with a fluence value of 1 × 10¹⁴ ions/cm². The diffraction curves of the irradiated crystals suggest the possibility of creation of low angle grain boundaries and other point/clusters of defects causing amorphization in the irradiated crystals. The perfection of the irradiated and unirradiated (0001) cleaved surfaces of the crystals is studied using the bulk method of X-ray topography. The topographs supplement the findings suggestive of modifications in the crystalline quality of SrFe₁₂O₁₉ on irradiation with SHI of Li^3?+?. Etching of the (0001) cleaved surfaces in H₃PO₄ at 120°C suggests that the dissolution characteristics of the surfaces get affected on irradiation with SHI of Li^3?+?, besides supporting the findings of HRXRD and X-ray topography regarding modifications in the perfection of SrFe₁₂O₁₉ on irradiation.     

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.     

The perfection of bridgman-grown Bi4Ge3O12 crystals

Single crystals of Bi₄Ge₃O₁₂ were grown by the vertical Bridgman technique. As shown by X-ray diffraction line profiles these crystals exhibit a very high degree of perfection. Bi₄Ge₃O₁₂ is used as detector material for high energy radiation. Very perfect crystals are preferred because defects play a prominent role in radiation damage.     

Relationship between the Optical Damage Resistance and Radiation Hardness and the Influence of Threshold Effects on the Radiation Hardness of ZnO-Doped LiNbO<Subscript>3</Subscript> Crystals

The radiation hardness and optical characteristics of beta-and gamma-irradiated LiNbO₃〈ZnO〉 crystals have been studied in a wide range of doping levels: ~0.04–5.9 mol % ZnO. The optical absorption (transmission) of the beta-and gamma-irradiated LiNbO₃〈ZnO〉 crystals has been evaluated as a function of the type and dose of radiation and dopant concentration. The optical damage resistance and radiation hardness of the crystals have been shown to be interrelated and depend on threshold effects in the LiNbO₃〈ZnO〉 crystals.     

Hydrogen and its radiation effects in quartz crystals

This paper presents near infrared absorption measurements (in the region of 3100-3700 cm(-1)) on quartz crystals to characterize the aluminum- and alkali-related hydroxyl defects in a variety of natural and cultured quartz crystals. Quartz samples were irradiated with an electron beam of 1.75 MeV and a dose of 2 Mrad at 77 K before and after irradiation at 300 K. The alkalis in quartz move under irradiation field only if the sample temperature is about or above 200 K, but the protons move at all temperatures down to 10 K. Therefore, irradiation at 300 K allows movement of both, protons and alkali ions, thus breaking away the aluminum-alkali centers into a mixture of Al-OH (-) and Al-hole centers. The natural quartz crystals have been measured with nearly similar Al and widely varying H-levels. For a similar radiation dose at 300 K, contrary to expectation, a lesser number of Al-OH(-) centers were produced in crystal with higher H-level than the sample with low-H quartz. At the present stage of work, we expect that this may be due to jamming in the kinetics of large number of protons in high-H crystals for steric reasons, which prevents them from reaching Al-sites after irradiation.     

Y3+:PbWO4晶体低剂量辐照行为研究

三价稀土离子（La^3 ,Lu^3 ,和Y^3 等）掺杂显著地提高了钨酸铅晶体的辐照硬度,但是部分Y^3 掺杂钨酸铅晶体表现出特殊的低剂量辐照行为,即光产额辐照后升高,并且辐照硬度对退火温度较敏感,研究研究挑选了存在这一现象的Y^3 :PbWO4晶体,测试冰同温度的退火处理对晶体透过率,光产额和辐照硬度的关系,发现,辐照后光产额升高的现象同时存在于晶体的晶种端,而不是只集中在晶体顶端,并且和辐照前后晶体在400－500nm波段附近的透过率变化有关;生长态Y^3 :PbWO4晶体中导致430nm吸收带的色心的稳定性很低,低剂量辐照对该色心有“漂白”作用,辐照剂量率加大则晶体表现出光产额的降低,分段晶体的系列退火实验解释了辐照硬度对退火温度较为敏感这一现象,为进一步深入研究提供了实验基础。     

The effect of radiation on twinning in quartz

The Dauphine twinning behavior of quartz subjected to irradiation was studied at room temperature and elevated temperatures. The presence of defects produced by irradiation was utilized to pin the domain wall motion. Both neutrons and gamma-rays were employed for this investigation. The stress required to nucleate an appreciable volume of twins is about twice as high for irradiated crystals than those unirradiated. However, the coercive stress required for causing a complete orientation switch was not much different between irradiated and unirradiated crystals.     

The microscopic theory of diffusion-controlled defect aggregation

The kinetics of diffusion-controlled aggregation of primary Frenkel defects (F and H centers) in irradiated CaF₂ crystals is theoretically studied. Microscopic theory is based on the discrete-lattice formalism for the single defect densities (concentrations) and the coupled joint densities of similar and dissimilar defects treated in terms of the Kirkwood superposition approximation. Conditions and dynamics of the efficient F center aggregation during crystal heating after irradiation are analyzed.     

X-ray-induced conductivity in gallium sesqui-selenide

The X-ray-induced dc conductivity of gallium sesqui-selenide (Ga₂Se₃) crystals characterized by anomalously high radiation resistance was studied as a function of the intensity of incident radiation. The obtained results show that Ga₂Se₃ crystals can be used as working elements of detectors for X-ray dosimetry in the range of radiation intensities studied.     

Y3+:PbWO4晶体低剂量辐照行为研究

三价稀土离子(Ｌａ^３＋、Ｌｕ^３＋和Ｙ^３＋等)掺杂显著地提高了钨酸铅晶体的辐照硬度,但是部分Ｙ^３＋掺杂钨酸铅晶体表现出特殊的低剂量辐照行为,即光产额辐照后升高,并且辐照硬度对退火温度较敏感 本研究挑选了存在这一现象的Ｙ^３＋:ＰｂＷＯ_４晶体,测试不同温度的退火处理对晶体透过率、光产额和辐照硬度的关系,发现:辐照后光产额升高的现象同时存在于晶体的晶种端,而不是只集中在晶体顶端,并且和辐照前后晶体在４００~５００ｕｍ波段附近的透过率变化有关;生长态Ｙ^３＋:ＰＷＯ晶体中导致４３０ｕｍ吸收带的色心的稳定性很低,低剂量辐照对该色心有“漂白”作用,辐照剂量率加大则晶体表现出光产额的降低;分段晶体的系列退火实验解释了辐照硬度对退火温度较为敏感这一现象,为进一步深入研究提供了实验基础．     

Properties of colour centres in CaF2 single crystals subjected to high electric fields and X-ray irradiation

Optical absorption in the region 200 to 680 nm, and thermoluminescence, have been studied for CaF₂ single crystals subjected to high d.c. fields (up to 70 kV cm^–1) and later irradiated with X-rays for 2 h. Similar data were also taken when the crystals were X-ray-irradiated under high d.c. or a.c. fields. Under both conditions, absorption bands with peaks at 375 and 580 nm were obtained. Partial thermal bleaching measurements carried out on the optical absorption of CaF₂ crystals subjected to a 50 kV cm^–1 d.c. field and later irradiated with X-rays indicate no correlation between the destruction of the colour centres (responsible for the absorption bands) and the thermoluminescence exhibited by these samples. It is noticed that the influence of high d.c. or a.c. field on the colour centre concentration is different depending on whether the CaF₂ crystals are first subjected to the field and later X-ray irradiated, or are X-ray irradiated under the fields.