Transport properties of overdoped Tl cuprates

To explain the observed inconsistency between the negative thermopowerS and the positive Hall coefficientR _H in the overdoped Tl cuprates, tight binding calculations are performed which include both Cu-O and O-O interactions in the CuO₂ square lattice. A striking feature of the CuO₂ antibonding band is that a holelike Fermi surface is formed even when the band is less than half-filled. This brings about an unusual electron state in which the Hall (cyclotron) mass along the Fermi surface is holelike but the transport mass perpendicular to it is electronlike. This electronlike transport mass contributes to the negative thermopower.We thank N. Hamada, T. Manako, and T. Kondo for helpful discussions.     

NaI(Tl) 闪烁谱仪峰总比的蒙特卡罗计算

简单分析NaI(Tl）闪烁谱仪探测原理的基础上，运用蒙特卡罗程序MCNP计算了该谱仪对不同能量点源的峰总比（或光分数），并同实验结果做了对比，解释了计算结果比实验值偏高的原因。     

NaI(Tl)γ谱仪测量数据的计算机处理方法

本文介绍了使用NaI(T1)γ谱线在铅室内分析环境土壤样品和就地γ辐射谱测量的刻度方法,以及专用微机解谱程序的功能和使用方法。     

Oxidation kinetics of bismuth and its dilute alloys

The oxidation behavior of high-purity poly crystalline bismuth in air has been investigated between 500 and 530° K for exposure times up to 20,000 min. The weight gain at a given temperature follows a parabolic kinetic law between 10 and 100 min, after which the rate abruptly decreases; the degree of this drop becomes greater the higher the temperature. Introduction of moisture in air increases the rate constant without changing the apparent activation energy for oxidation. The addition of as little as 0.1 at.% Pb, Sb, Tl, In, Te, or Sn completely eliminates the 100 min transition observed in pure bismuth, and radically changes the oxidation parameters. The results are explained in terms of an amorphous oxide layer which can form dangling bonds in the presence of moisture, or can be doped by the addition of appropriate impurities to the metal.     

NaI(Tl)γ谱的计算机稳峰技术

介绍了一种改进型NaI(Tl)γ谱仪的稳谱技术。该稳谱技术基于241Am源的等效γ峰作为系统的参考峰,根据参考峰位偏差运用数字PID调整可编程增益放大器来稳谱,是一种“硬件 参考源 软件”的稳谱技术。这种计算机稳谱技术具有稳定度高,稳谱速度快等优点。     

硅PIN光敏二极管探测X、γ射线的性能及应用

介绍了硅PIN光敏二极管和电荷灵敏前放组成的X射线探测器和配合CsI(Tl)晶体构成的γ射线探测器的性能和测量结果,同时研究了光敏二极管探测器能量分辨率的温度特性。测量X射线时,在-10℃下对241Am的59.5keV射线的能量分辨率为4.8%;用PIN光敏二极管配合10mm×10mm×10mm的CsI(Tl)晶体测量γ射线时,在20℃下对137Cs0.662MeVγ射线的能量分辨率为9.9%,60Co的1.332MeVγ射线的能量分辨率为6.4%,-10℃下的能量分辨率分别为8.7%和6.3%。     

LiMn1.90Tl0.05Al0.02Cr0.03O4的合成及电化学性能

以Li2 CO3 、电解MnO2 、TlNO3 、Al(NO3 ) 3 ·9H2 O和Cr(NO3 ) 3 ·9H2 O为原料 ,采用湿化学分散与中温固相反应法制备了LiMn1.90 Tl0 .0 5Al0 .0 2 Cr0 .0 3 O4锂离子蓄电池正极材料 ,并采用XRD、TEM、SEM和电化学性能测试对该正极材料进行了表征。结果表明 ,由Tl、Al和Cr原子取代部分Mn原子的复合正极材料仍呈尖晶石结构 ,未观察到分离的Tl、Al和Cr及其氧化物的XRD峰 ,材料呈完整立方晶体结构 ,表面分布均匀 ,电化学性能稳定。在常温下 ,首次放电容量大于115mAh/g ,循环 75次后 ,放电容量仍保持在 110mAh/g。在高温 (5 5℃ )下 ,首次放电容量仍大于 115mAh/g ,循环 40次后 ,放电容量保持在大于 10 5mAh/g ,表现出较高的循环可逆性和高温稳定性。     

Improvement of an Energy Spectrum by Means of a Timing Technique

Abstract

The constant fraction (CF) discrimination technique was applied to gamma rays emitted from a gamma source via a developed spectrometer. Experimental energy spectra, with and without the CF discrimination technique, were obtained separately. After the application of the technique, the spurious radiations on the low energy tail of the energy spectrum which had arisen from the low‐energy background, backscattering and Compton radiations were partly discriminated, leading to improvement in the energy spectrum.     

G(E)法与Gravel法处理能谱-剂量转换效果研究

为准确地得到γ射线的辐射剂量,对G(E)函数法和Gravel算法处理能谱-剂量的转换效果进行了研究。根据实际应用需求,采取蒙特卡罗方法模拟获取了?50 mm×50 mm NaI(Tl)探测器的Gravel法响应矩阵,并使用Matlab得到探测器的G(E)函数。使用NaI(Tl)探测器和多道谱仪系统测量标准源的能谱,分别使用G(E)法和Gravel法计算剂量值并与理论值进行比较,同时在计算过程中总结对比了两种方法的特点。