PPM量级纹波系数的光电倍增管恒流源

本文讨论的光电倍增管高压电源是针对其纹波要求较苛刻而工作时间较短的特殊场合而设计的。该电路可提供输出稳定、纹波系数小的直流高压、它能保证光电倍增管在工作时间内的良好工作。实验结果证明该电路确实可行。     

真空紫外微通道板光电倍增管的研制

主要讨论了真空紫外微通道板光电倍增管的工作原理及设计考虑,介绍了这种新型弱光探测器研制过程中的主要关键技术以及该器件所具有良好性能和广阔的应用前景。     

双微通道板光电倍增管的研究

通过对双微通道板级联技术的研究 ,研制出脉冲上升时间小于 1ns ,增益大于 5× 10 5的微通道板光电倍增管。这种管子在天文学、高能物理实验等领域有广泛的应用前景     

紫外多阳极(128×128)微通道阵列光电倍增管的研制

详细报道了新研制的紫外多阳极微通道阵列光电倍增管。该器件采用了叠合式阵列阳极(128×128)、端窗式“日盲”紫外光电阴极(碲铷RbTe)、高增益的Z型微通道板组件、近贴聚焦结构等先进技术。器件的主要性能参数为阴极发射灵敏度18 mA/W,增益2×10     

Determination of correction factors for borehole natural gamma-ray measurements by Monte Carlo simulations

The analysis of natural γ-ray spectra measured in boreholes has to take into account borehole parameters such as the presence of casings and borehole diameter. For large, high-efficiency γ-ray detectors, such as BGO-based systems, which employ full-spectrum data analysis, corresponding corrections were not previously determined. In a joint project of the Nuclear Geophysics Division of the Kernfysisch Versneller Instituut (NGD/KVI), Groningen, Medusa Explorations B.V. and the Dutch Institute for Applied Geosciences (TNO-NITG) a catalogue of corrections was constructed. Using the Monte Carlo code MCNP, the influence of steel casings, borehole diameter, central axis probe position and the diameter of the γ-ray detector on the γ-ray spectra has been investigated for nearly 20 geometries. The calculated γ-ray spectra are compared qualitatively and quantitatively. In a case study, γ-ray spectra from a borehole measured in a cased and uncased configuration are analyzed with simulated spectra. When no corrections are used, the activity concentrations deviated by as much as 50% between the two measurements. Taking into account the specific measurement geometry, the activity concentrations were found to be identical within the statistical and systematic uncertainties of the experiment for the same borehole, with and without casing. These results illustrate the need for borehole-specific corrections and this study demonstrates that Monte Carlo methods are a fast and reliable way to calibrate well-logging tools for a wide variety of configurations.     

γ射线辐照对类金刚石薄膜结构与特性的影响

用射频等离子体方法在玻璃基底上制备了类金刚石薄膜。分析了γ射线辐照类金刚石薄膜（以下简称ＤＬＣ薄膜）的结构与特性改变。采用Ｒａｍａｎ及红外光谱进行结构分析表明：随辐照剂量的增加,在膜中出现ＳＰ３Ｃ—Ｈ及 ＳＰ２Ｃ—Ｈ 键的断裂与减少,ＳＰ３Ｃ—Ｃ键的略微增加．当辐照剂量达 １０ ×１０４Ｇｙ时,ＳＰ３Ｃ—Ｈ键减少约５０％,与此同时,出现膜中氢的重新键合,并从中释出。γ射线辐照使ＤＬＣ薄膜的电阻率呈上升趋势,膜的类金刚石特征更加明显,结构得到改善。本文对γ射线对ＤＬＣ薄膜的辐照机制进行了简要的讨论。     

Determination of natural radioactivity in building materials used in Tunisian dwellings by gamma ray spectrometry

The radioisotopic content of 17 samples of natural and manufactured building materials collected in Tunisia have been analysed by using gamma spectrometry. From the measured gamma ray spectra, activity concentrations are determined for (232)Th, (226)Ra, (235)U and (40)K. The total effective dose and the activity concentration index are calculated applying the dose criteria recommended by the European Union for building materials. The results of (226)Ra, (232)Th and (40)K found in Tunisian building materials indicate that radium and thorium concentrations do not exceed 40 Bq kg(-1), but potassium concentration varies between 50 and 1215 Bq kg(-1). The total effective dose rates per person indoors are determined to be between 0.07 and 0.86 mSv y(-1). Only two materials exceed the reference level of 0.3 mSv y(-1). The activity concentration index is <1.     

Time jitter influence on the performance of gamma–gamma turbulence FSO links with various modulation schemes

ABSTRACT

The research area of optical wireless communication links has attracted significant interest over the last years due to the significant advantages offered by this kind of technology. However, the performance of FSO communication systems depends strongly on the effects, which are related to the atmosphere along the propagation path such FSO links are using. More specifically, the weather conditions and atmospheric turbulence effects can deteriorate considerably the performance characteristics. In this work, we are studying the joint influence of atmospheric turbulence and time jitter effects on the average BER of an FSO link by presenting a new approach for various modulation schemes. Thus new closed-form mathematical expressions are derived for accurate estimation of the BER performance of the optical wireless communication systems. Finally, using the obtained expressions and typical parameter values for FSO links, the numerical results are presented and then verified through Monte Carlo simulations.     

Solution growth of cadmium telluride

Cadmium telluride crystal has been grown by solution method from Te-rich (Cd_0·3Te_0·7) melt. Ingots having 9 mm diameter and length up to 30 mm were grown by cooling the melt slowly (1°C/h) under a vertical temperature gradient of about 30°C/cm. As-grown ingots were characterized for optical transmission and resistivity. The middle portion of the ingots exhibited better optical transmission properties. Resistivity (p-type) was found increasing, towards the last-to-grow end, from 10³ to 10⁶ Θ-cm. Surface barrier type of detectors, made from low resistivity (≅ 10⁴Θ-cm) materials, were found suitable for detection ofX- and low energy gamma radiations. In case of high resistivity (≅10⁶Θ-cm) detectors, the performance was seen to be affected by polarization. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

Development of pure and doped gamma ferric oxide

Optimum conditions and experimental details for the formation of γ-Fe₂O₃ from goethite have been worked out. In another method, a cheap complexing medium of starch was employed for precipitating acicular ferrous oxalate, which on decomposition in nitrogen and subsequent oxidation yielded acicular γ-Fe₂O₃. On the basis of thermal decomposition in dry and moist nitrogen,dta, xrd, gc and thermodynamic arguments, the mechanism of decomposition was elucidated. New materials obtained by doping γ-Fe₂O₃ with 1–16 atomic percent magnesiu, cobalt, nickel and copper, were synthesised and characterized.     

Effect of gamma irradiation and silver doping on YBCO superconductor

The effect of -irradiation and silver doping on the properties of YBCO superconductors has been studied by electrical resistance measurements and x-ray diffraction techniques. The zero-resistance superconducting transition temperature of (YBCO)_1–xAg _x systematically increase by about 2 K with an increase of Ag content up tox=0.04. Further increase in Ag content decreases the transition temperature. The normal-state resistance decreases up to a factor of 3.4 with an increase of Ag content. No significant change in the transition width has been observed due to silver addition up tox=0.30. Undoped YBCO and the Ag-doped specimens of (YBCO)_1.96Ag_0.04 were irradiated with-rays up to an integrated-dose of 77 MR. The normal-state resistance of the specimens gradually increases and the transition temperature slightly decreases with increase of-dose. The intensities of the x-ray diffraction peaks of the monolayers of the sample powders decrease with -irradiation without noticeable change of diffraction angles or peak widths. These observations indicate that the high-T _c supconductor YBCO is quite sensitive to-irradiation but drastic lattice expansion does not occur up to a-dose of 77 MR.     

Determination of selenium in natural waters by adsorptive differential pulse cathodic stripping voltammetry

In this work bovine albumin was used innovatively as a medium for adsorptive accumulation of Se–I₂ on thin mercury film electrode. Se–I₂ was formed by reaction between Se(IV) and iodide in HCl media. The adsorbed Se–I₂ was stripped in 0.05 M HCl by differential pulse cathodic potential scan. The proposed method was successfully applied to analysis of Se(IV) and Se(VI) in natural waters sampled from some lagoons south of Caspian Sea. The optimum reaction conditions and other analytical parameters and influence of cations and anions were studied. The detection limit was 0.37 ng mL⁻¹. The obtained results were compared with the results of DPCSV after electrochemical preconcentration, HG-AAS and ICP-AES.     

Comparison of radiation damage in lead tungstate crystals under pion and gamma irradiation

Studies of the radiation hardness of lead tungstate crystals produced by the Bogoroditsk Techno-Chemical Plant in Russia and the Shanghai Institute of Ceramics in China have been carried out at IHEP, Protvino. The crystals were irradiated by a 40 GeV pion beam. After full recovery, the same crystals were irradiated using a ¹³⁷Cs γ-ray source. The dose rate profiles along the crystal length were observed to be quite similar. We compare the effects of the two types of radiation on the crystal's light output.     

工业γ射线探伤的辐射防护措施

通过对典型工业γ射线探伤室周围的现场监测,将探伤室周围的辐射吸收空气剂量率与GBZ132-2008中规定的剂量限值进行比较,进行了固定式γ射线探伤辐射防护措施的可行性分析。同时通过理论计算得到了使用放射源探伤时无防护措施可能造成的超大辐射剂量照射数据,有效印证了进行有效硬件防护以及与软件措施相结合,就能够在γ射线探伤实践中保护环境和从业人员的安全,同时也为管理部门提供技术支持。