溴化镧探测器时间分辨率的测量

用60 Coγ源和搭建的电子学测量系统,测量了自制塑料闪烁探测器、3英寸的溴化镧探测器和电子学系统的时间分辨率,得到了圣戈班公司生产的3英寸溴化镧探测器的时间分辨率为(283.2±0.9)ps.     

掺镧方钴矿型晶体的拉曼光谱测定

本文用熔融退火法生长了热电材料掺镧方钴矿 (LaxFe3CoSb12 )晶体。用背散射方法测定了不同掺镧量晶体的拉曼光谱。我们认为稀土镧原子占据了方钴矿结构中的空位 ,这些填充空位的离子参与结构中的晶格振动 ,使拉曼谱线位移并加宽。随着含镧量的增加 ,镧原子振颤自由度降低 ,谱线的加宽程度减小。     

晶体电光和非线性光学效应的离子基团理论(Ⅳ) 钙钛矿、钨青铜型、LiNbO_3型晶体线性极化率计算

本文再次采用氧八面体基团模型及定域化轨道波函数的方法系统地计算了九种钙钛矿、钨青铜型和LiNbO_3型晶体的折射率。在未引入任何可调整参量的情况下,计算值与实验值之差仅10%左右。由此可见,氧八面体基团模型及定域化轨道波函数的计算方法不但能在定量上阐明这两种类型材料的电光和非线性光学效应的机理,同时也能阐明光频线性极化率的各种性质。本文的计算还表明,虽然奇次项晶格场是晶体产生电光和非线性光学效应的决定因素,但对线性极化率的影响恰非常小。最后,就定域化轨道方法的可靠性作了某些讨论。     

CdS0.1Se0.9纳米晶体共振电吸收谱的线形分析

采用电调制技术在室温下测量了 Cd S0 .1 Se0 .9纳米晶体的电吸收谱 ,并对电吸收谱线形进行了分析。纳米晶体与第一个吸收峰有关的电吸收谱结构具有吸收系数对能量的二阶微商特征 ,表明第一激发态在电场作用下以吸收谱线的宽化为主 ,而纳米晶体尺寸不单一是吸收谱线宽化的主要因素。共振电光响应信号的峰值位置、过零点位置以及电吸收谱的线形几乎不随外电场强度而变化 ,信号幅度随外电场强度的平方线性增加。 Cd S0 .1 Se0 .9纳米晶体的电光效应是Kerr效应 ,纳米晶体具有三阶非线性光学极化率 Χ( 3 )。     

晶体电光和非线性光学效应的离子基团理论(Ⅳ)——钙钛矿、钨青铜型、LiNbO3型晶体线性极化率计算

本文再次采用氧八面体基团模型及定域化轨道波函数的方法系统地计算了九种钙钛矿、钨青铜型和LiNbO₃型晶体的折射率。在未引入任何可调整参量的情况下,计算值与实验值之差仅10%左右。由此可见,氧八面体基团模型及定域化轨道波函数的计算方法不但能在定量上阐明这两种类型材料的电光和非线性光学效应的机理,同时也能阐明光频线性极化率的各种性质。本文的计算还表明,虽然奇次项晶格场是晶体产生电光和非线性光学效应的决定因素,但对线性极化率的影响恰非常小。最后,就定域化轨道方法的可靠性作了某些讨论。     

非线性光子晶体中光敏超棱镜现象的研究

基于非线性时域有限差分法,模拟了克尔非线性光子晶体中的光敏超棱镜现象.结果发现,当光强变化230 W/μm时,两束光在空间上能被分开10°,选取较大的基本功率将有助于提高其光强分辨率. 而且,当自抽运光较强时,光子晶体中光波的波矢方向将会发生转动. 此外,光束在非线性光子晶体中长距离传播时,透过率的变化将经历几个不同的阶段,分别对应于不同原因所造成的光强损耗. 关键词： 光子晶体 超棱镜 克尔非线性效应     

[Bmim]Br3与β-二羰基化合物的选择性溴化反应研究

研究离子液体三溴化1-丁基-3-甲基咪唑[Bmim]Br3对乙酰丙酮、乙酰乙酸乙酯、丙二酸二乙酯等羰基化合物的α-溴化反应。在无催化剂、溶剂条件下,[Bmim]Br3对以上几种羰基化合物溴化,高产率、高选择性地得到α-溴化产物,产率为93%—96%。实验结果表明,在离子液体[Bmim]Br3存在下,溴化反应不仅速度较快、温度缓和、操作简便,而且产物的产率高、易分离、对环境更友好。本方法提供了一个区域选择性好、简单、方便合成α-溴化β-二羰基化合物的方法。     

晶体塑性有限元在材料动态响应研究中的应用进展

作为连续尺度上描述各向异性非均质材料弹塑性变形的重要模拟工具,晶体塑性有限元能够有效预测材料的宏观力学性能,在工程设计方面起着重要的作用。在实际工程应用中,许多晶体材料在高应力、高变形率、高温等极端条件下服役,此时各向异性非均匀的微介观结构演化是理解材料动态响应的关键,这给晶体塑性有限元带来了巨大的机遇和挑战。首先简要综述了晶体塑性有限元的原理和方法,然后着重介绍其在材料动态响应中的应用,最后展望其在材料动态响应模拟方面的发展方向。     

环境本底伽马辐射的实验测量

使用高纯锗与溴化镧探测器,在无标准放射源的情况下,可以对环境中的伽马辐射本底进行高精度的实验测量,进而实现对环境中主要放射性成分的粒子鉴别.     

6×6BGO晶体阵列电磁量能器的研制及低能光子测量

研制了6×6锗酸铋晶体阵列式探测器,作为高分辨全吸收电磁量能器模型.晶体阵列由36块截面为20mm×20mm、长度为200mm的国产锗酸铋晶体组成,采用光电倍增管读出,从阳极及一个打拿极同时输出讯号,以满足大动态范围线性要求.在静电加速器上应用若干(p,γ)反应产生的单能光子进行了测试.结果表明:在所测21MeV以下范围内,能量响应线性;能量分辨率表现为予期的E^－1/2关系,与国际上现有同类装置比较具有最佳能量分辨性能.     

Plastics as nuclear track detectors for thermal neutron dosimetry

An attempt is made to determine the response of CR-39 and cellulose nitrate plastic track detectors subjected to thermal neutrons. The α-particles are produced from (n, α) reactions in lithium tetraborate convertor placed in contact with different plastics and are recorded in the detectors. The corrected track density gives a fluence sensitivity and dose sensitivity of the order of 10^?4 tracks per neutron and 10² tracks/cm² mrem respectively. A linear relationship is observed between track density and neutron fluence.     

溴化镧闪烁体探测器性能及应用研究

LaBr3(Ce)探测器是一种新型闪烁体探测器,具有高光产额,高探测效率,高时间和空间分辨率,高能量分辨率,温度特性良好,抗辐射性能良好,操作简便等优点.从2001年以来,该探测器得到了迅速的研究和应用.LaBr3(Ce)探测器在核共振荧光检测、瞬发γ中子活化分析、爆炸物检测、核医学成像、环境辐射监测、空间辐射探测等方面的应用研究中取得了非常良好的效果.该探测器表现出优于以往用于这些领域的探测器的性能(例如NaI(Tl)探测器、BGO探测器、HPGe探测器等).介绍了LaBr3(Ce)探测器的性能及其应用研究进展,对代表性文献进行了简析和综述,阐明了其良好的应用前景.     

Quantum teleportation with a three-Bell-state analyzer

We present a novel Bell-state analyzer (BSA) for time-bin qubits allowing the detection of three out of four Bell states with linear optics, two detectors, and no auxiliary photons. The theoretical success rate of this scheme is 50%. Our new BSA demonstrates the power of generalized quantum measurements, known as positive operator valued measurements. A teleportation experiment was performed to demonstrate its functionality. We also present a teleportation experiment with a fidelity larger than the cloning limit.     

Using a LaBr3:Ce scintillator for positron annihilation lifetime spectroscopy

A LaBr₃:Ce scintillator has a high light output (~60000 p.e/MeV) and a short decay constant (<25 ns), which makes it good for time spectrometry. Compared with a BaF₂ scintillator, it can bear a much higher count rate, and can be coupled to photomultipliers without using a quartz window. In this work, a positron annihilation lifetime spectrometer (PALS) consisting of two bulks of φ25 mm×25 mm LaBr₃:Ce scintillator coupled to two XP20D0 photomultipliers, respectively, was built. A time resolution of FWHM=206 ps was measured for the PALS with a ⁶⁰Co source at the energy window for ²²Na. With this spectrometer, a reasonable lifetime value τ=221±4 ps in a pure Si sample is obtained, which means that the utilization of LaBr₃:Ce as the detector for a PALS is feasible.     

Waveform digitizing for LaBr_3/NaI phoswich detector

The detection efficiency of phoswich detector starts to decrease when Compton scattering becomes significant. Events with energy deposit in both scintillators, if not rejected, are not useful for spectral analysis as the full energy of the incident photon cannot be reconstructed with conventional readout. We show that once the system response is carefully calibrated, the full energy of those double deposit events can be reconstructed using a waveform digitizer as the readout. Our experiment suggests that the efficiency of a photopeak at 662 keV can be increased by a factor of 2 using our LaBr₃/NaI phoswich detector.     

High-accuracy fluence determination in ion beams using fluorescent nuclear track detectors

We present an approach to use Al₂O₃:C,Mg-based fluorescent nuclear track detectors (FNTDs) and confocal laser scanning microscopy as a semiautomatic tool for fluence measurements in clinical ion beams. The method was found to cover a linear energy transfer (LET) range from at least L_∞(Al₂O₃) = 0.5 keV/μm to 61,000 keV/μm with a detection efficiency ≥99.83% (20 MeV protons) at particle fluences up to at least 5 × 10⁷ per cm². Our technique allows to determine the spatial fluence distribution on a microscopic scale and enables detailed track-by-track comparison studies between different fluence detectors.     

Measuring fluence of fast neutrons with planar silicon detectors

The results of measurements of 1-MeV (Si) equivalent fast neutron fluence with silicon planar detectors are reported. The measurement method is based on the linear dependence of the reverse detector current increment on the neutron fluence: ΔI = α _I × Φ × V. This technique provides an opportunity to measure the equivalent fluence in a wide dynamic range from 108 to 10¹⁶ cm^–2 with an unknown neutron energy spectrum and without detector calibration. The proposed method was used for monitoring in radiation resistance tests of different detector types at channel no. 3 of IBR-2 and for determining the fluence of fission and leakage neutrons at the KVINTA setup.     

Effects of radiations on the characteristics of alpha and fission tracks in CR-39 detectors

Abstract

The effects of neutron, gamma and alpha radiations on the alpha and fission fragment tracks registration and revelation properties of CR-39 detectors (CR-39 and CR-39(DOP) were studied. It was found that the ratio of the bulk etch rate of irradiated to unirradiated (V_G(irr.)/V_G(unirr.) detectors is linearly dependent on dose. An exponential decrease in fission track densities with increase in neutron fluence was observed. The ratio of V_G(irr.)/V_G(unirr.) was found to be high in CR-39 than that in CR-39(DOP) exposed to the same reactor neutron fluence. The decrease in fission track densities with increase in neutron fluence was observed to be faster in CR-39 than in CR-39(DOP). This indicates that doping with dioctyl phthalate improves the radiation resistance of CR-39 detectors. It was observed that in detectors exposed to an alpha flux of the order of 9.36 × 10⁶ / cm², the fission track density was reduced by 11% and thereafter it remained constant. The results also indicate that thermal neutron fluence up to 7.01 ×10¹¹ neutrons/cm² does not affect the alpha and fission track densities. I.R. spectra were also studied to find out the nature of chemical changes produced by these radiations on CR-39.     

用于高能X光测量的Si-PIN阵列探测器

设计了用于高能X光测量的小面积PIN硅光电二极管线列探测器,通过理论计算和EGSnrc蒙卡软件模拟分析了Si-PIN的探测灵敏度、线性电流和时间响应。根据理论研究可知,该探测器适用于大注量率、高能轫致辐射光的空间分辨力(3 mm)和时间分辨力(8 ns)的测量。并在理论设计的基础上进行了部分实验,采用小面积PIN硅光电二极管和放大电路,在"神龙一号"直线感应加速器上进行高能X光的测量,初步得到了PIN硅光电单元的响应结果,为线列小面积PIN光电管阵列的实用设计提供优化基础。     

The effect of fast neutrons on the conductance of single-crystal silicon

The dependence of variation of the specific conductance of single-crystal silicon on the fast neutron fluence is calculated. The results of calculations are compared with the experimental data obtained in two channels of an IRT-T reactor with different neutron spectra. These experimental data are also discussed. The fast neutron fluence was controlled using threshold sulfur activation detectors. The specific electrical resistance was measured by a 4-probe method. The calculation data are in good agreement with experiment and show that the variation of the specific conductance due to exposure to fast neutrons is in direct proportion to the fluence of these neutrons. The proportionality coefficient depends on the neutron spectrum, but is independent of the initial specific conductance. In so doing, it makes no difference, whether silicon was previously irradiated or not.