Well-type phoswich counter for low-flux X-ray/γ-ray detection

Phoswich counters that can detect low-flux hard-X-ray/γ-ray from localized sources are described. The counter consists of a small inorganic scintillator with a fast decay time (the detection part) glued to the interior bottom surface of a well-shaped block of another inorganic scintillator with a slow decay time (the shielding part). The first model counter was built by using a new scintillator, gadolinium silicate (GSO), in the decision part and CsI(Tl) in the shielding part. A detector system consisting of 64 such phoswich counters (total area ~740 cm²) was flown onboard a balloon, setting a limit to the ⁵⁷Co line flux from SN 1987A, at ~10^-4 cm^-2 s The sensitivity for continuum flux was around a few ×10 ^-6 cm^-2 s^-1 keV^-1 between 100 and 200 keV. In the second model, CsI(Tl) was replaced by bismuth germanate (BGO), and radioactive contaminations in GSO were reduced. Improvements are planned to reach a sensitivity (3σ) around 5×10^-7 cm^-1 s^-1 keV^-1 for the continuum     

利用测热技术测量核反应堆中子通量密度

一种新型中子探测器被研究,其原理是利用带电离子在矿物中沉积的能量退火时会以热量的方式释放出来,通过测量释放的热量而确定中子通量密度。对新型中子探测器进行刻度,在反应堆内某位置测量的热中子通量密度为5.108×10¹¹ cm^-2•s^-1,与标定的热中子通量密度(5.000×10¹¹ cm^-2•s^-1)在2%内符合,说明该探测器可测量中子通量密度。本文方法制作的探测器体积小,可制作成不同形状,便于反应堆不同环境下的中子通量密度测量。选取相应中子能量反应截面较大的元素,该探测器还可测量不同中子能量的通量密度。     

堆内超临界水回路辐照装置物理参数模拟研究

堆内超临界水回路对我国超临界水堆燃料和结构材料的辐照腐蚀实验具有重要意义,辐照装置位于反应堆堆芯栅格,是超临界水回路的核心部件。采用MCNP程序模拟研究辐照装置的关键物理参数,并考虑超临界水热物特性对物理参数的反馈效应。计算得到辐照装置热中子注量率为4.72×10¹³ cm^-2•s^-1,快中子注量率为1.55×10¹⁴ cm^-2•s^-1,辐照产热率为14.7 kW,反应性引入为0.045%。     

Neutron-induced radiation damage in silicon detectors

Ion-implanted silicon pad detectors fabricated on different n-type and p-type silicon wafers with initial resistivities between 2.6 and 12.9 kΩcm were irradiated with neutrons of ~1 MeV energy, up to a fluence of 5×10¹³ n cm^-2. The evolution of diode leakage current and capacitance characteristics is presented as a function of the neutron fluence. The reverse diode current increases proportionally to the neutron fluence. There is evidence that the doping of the initial n-type material evolves towards intrinsic and inverts to an apparent p-type at fluences between 1×10¹³ and 3×10¹³ n cm^-2, depending on the initial silicon resistivity. There is also evidence that p-type material remains of the same conduction type with a slight increase of the acceptor doping with fluence. The signal shape and the charge collection efficiency for incident β particles were measured     

低能电子辐照对环氧树脂性能的影响

为了研究低能电子辐照对环氧树脂的体积电阻率、邵氏硬度、拉伸强度和官能团结构的影响，本文在电子辐照能量为30 keV，注量率1×10¹¹ cm^-2•s^-1，总注量为1.6×10¹⁴ cm^-2，真空度10^-6 Pa条件下，结合国家标准对辐照前、后环氧树脂材料的机械性能和结构进行表征。结果表明，辐照后环氧树脂材料的体积电阻率、邵氏硬度、拉伸强度等宏观物理性能均有下降。傅里叶红外光谱图显示环氧树脂主要官能团强度降低，产生的•H、•OH等自由基与聚合物分子上的羟基与氢结合。研究结果对环氧树脂材料在辐射环境中的使用具有重要意义。     

用于n/γ混合场测量的涂硼电离室研制

研制了一种能同时测量混合场中γ和中子注量率的涂硼电离室,并实验测试了其性能。涂硼电离室由两个大小和结构一致的腔室组成：1个仅对γ灵敏,另1个对γ与中子均灵敏。用强度为2.7×10⁷ s^-1 的Am-Be源测得电离室的中子灵敏度达9.2×10^-16 A/(cm^-2•s^-1),在剂量率为5.24 μGy/h的¹³⁷Cs γ场中,电离室的γ灵敏度达7.36×10^-16 A/(MeV•cm^-2•s^-1)。涂硼电离室I-V曲线坪长为600 V,坪斜小于4%/100 V,在工作电压为-400 V时,其γ补偿修正系数<5%,可用于核设施周围的混合场监测。     

利用HFETR制备有载体177Lu

¹⁷⁷Lu是一种优良的诊疗一体化医用放射性核素,其标记的放射性药物被广泛用于多种癌症的诊断和治疗。其中,有载体¹⁷⁷Lu的制备具有放射化学处理简单、¹⁷⁷Lu产量高等优点。为此,在高通量工程试验堆(HFETR)中利用热中子辐照¹⁷⁶Lu,开展有载体¹⁷⁷Lu的制备研究。本研究分别辐照天然Lu和富集¹⁷⁶Lu进行热实验验证,结果表明：天然Lu在2×10¹⁴ n·cm^-2·s^-1热中子通量下辐照13 d,生成¹⁷⁷Lu比活度约为0.87 Ci/mg,^177mLu杂质含量为0.009%;富集(86.5%)¹⁷⁶Lu在热中子注量率为1×10¹⁴ n·cm^-2·s^-1条件下辐照28 d,生成¹⁷⁷Lu比活度约为24.9 Ci/mg,^177m...     

GIC4117串列加速器外束PIXE/PIGE分析系统

本文介绍在北京师范大学GIC4117串列加速器上建立的外束PIXE/PIGE分析系统,和基于此系统的薄样品外束PIXE/PIGE定量分析方法。给出了2010年Teflon滤膜采集的361个气溶胶样品外束PIXE分析得到的各元素平均探测限和最低探测限,并同真空PIXE分析探测限进行了比较。利用标准样品给出了激发曲线不同坪区薄样品外束PIGE分析F和Na的探测限,通过测定¹⁹F(p, p′γ)¹⁹F激发的197 keV γ射线得到的F的探测限可达73.9 ng•cm^-2,Na的探测限可达198.9 ng•cm^-2。     

Spectral Characteristics of Laser-Induced Graphite Plasma in Ambient Air

An experimental setup of laser-induced graphite plasma was built and the spectral characteristics and properties of graphite plasma were studied. From the temporal behavior of graphite plasma, the duration of CN partials(B~2∑~+→X~2∑~+) emission was two times longer than that of atomic carbon, and all intensities reached the maximum during the early stage from0.2 μs to 0.8 μs. The electron temperature decreased from 11807 K to 8755 K, the vibration temperature decreased from 8973 K to 6472 K, and the rotational temperature decreased from7288 K to 4491 K with the delay time, respectively. The effect of the laser energy was also studied, and it was found that the thresholds and spectral characteristics of CN molecular and C atomic spectroscopy presented great differences. At lower laser energies, the electron excited temperature, the electron density, the vibrational temperature and rotational temperature of CN partials increased rapidly. At higher laser energies, the increasing of electron excited temperature and electron density slow down, and the vibrational temperature and rotational temperature even trend to saturation due to plasma shielding and dissociation of CN molecules. The relationship among the three kinds of temperatures was T_(elec)T_(vib)T_(rot) at the same time. The electron density of the graphite plasma was in the order of 10~(17)cm~(-3) and 10~(18)cm~(-3).     

基于FPGA的高性能坎贝尔积分算法研究

为满足国际热核聚变实验堆的宽量程中子通量测量需求，设计了基于FPGA和交流耦合平方积分的高性能数字化坎贝尔积分算法，拥有更强γ抑制能力的同时将中子甄别系统的测量范围从10⁵ s^-1提高到10⁸ s^-1。结合²³⁵U裂变室及坎贝尔测量原理研究了数字化坎贝尔积分算法，通过仿中子脉冲实验分析了脉冲甄别计数算法和坎贝尔积分算法重叠区域的工作性能，并得出坎贝尔积分算法在不同噪声下的适用条件，从而保证测量相对误差小于5%。使用基于该算法的测量系统在HL-2A进行了现场实验，对照脉冲甄别计数算法的测量结果进行标定，二者一致性非常好，在测量重叠范围内线性系数达0.97。     

Progress of plasma density fluctuation measurements with phase contrast imaging on HL-2A tokamak

A CO₂ laser-based phase contrast imaging (PCI) diagnostic has been developed on HL-2A tokamak. It can detect line integrated plasma density fluctuations by measuring the phase shift of laser beam after being scattered by the bulk plasma. The diagnosed radial region ranges from \rho \equiv r / a = 0.625 to 0.7. 32-channel HgCdTe detectors with alternative-current biased amplifiers are arranged in line at the imaging plane of the optical path. This PCI is able to diagnose density fluctuations with wavenumbers ranging from 2 cm^-1 to 15 cm^-1 and the time resolution is better than 2 μs. The first experimental data were achieved in 2018 spring campaign of HL-2A tokamak. High performance is confirmed in different discharging configurations and makes it a keen tool in broadband turbulence investigations.     

Investigation of the radiation hardness on semiconductor devices using the ion micro-beam

Variation of the ion beam induced charge (IBIC) pulse heights due to ion irradiation was investigated on a Si pn diode and a 6H-SiC Schottky diode using a 2 Mev He⁺ micro-beam. Each diode was irradiated with a focused 2 MeV He⁺ micro-beam to a fluence in the range of 1×10⁹–1×10¹³ ions/cm². Charge pulse heights were analyzed as a function of the irradiation fluence. After a 2 MeV ion irradiation to the Si pn junction diode, the IBIC pulse height decreased by 15% at 9.2×10¹² ions/cm². For the SiC Schottky diode, with a fluence of 6.5×10¹² ions/cm², the IBIC pulse height decreased by 49%. Our results show that the IBIC method is applicable to evaluate irradiation damage of Si and SiC devices and has revealed differences in the radiation hardness of devices dependent on both structural and material.     

Effects of fast neutron radiation on polypropylene

Capacitor-grade polypropylene films were irradiated in a 2-MW thermal nuclear reactor and exposed to fast neutron radiation at a flux rate of 2.6×10¹² neutron/cm² s and gamma radiation at a level of 10⁷ rad/h. The postirradiation effects on changes in the electrical and chemical properties of the films were studied for irradiation times up to 10 h. The electrical properties were DC and AC breakdown voltages, life under pulsed voltage stress, dielectric permittivity, dielectric losses, and volume resistivity. Chemical analysis was performed using the infrared spectroscopy technique. Small changes were detected in the dielectric strength, dielectric properties, and volume resistivity of the film. These changes are believed to be caused by oxidation of the polypropylene film, as was evidenced by the infrared spectra showing an increase in the carbonyl absorption peak at 1720 cm^-1     

医院中子照射器中子束流出口处热中子注量率的测量

医院中子照射器是基于微型反应堆而设计的专门用于硼中子俘获治疗（BNCT）的核反应堆装置,其额定功率为30 kW。在堆芯相对两侧分别设有一条热中子束流和超热中子束流用于病人照射,在热中子束流内引出一条实验用热中子束流,用于瞬发γ法测量病人血硼浓度。本工作利用²³⁵U裂变靶和白云母探测片测量了热、超热和实验用热中子束流出口处的热中子绝对注量率。结果显示,在30 kW额定功率运行时,热、超热和实验用热中子束流出口处的热中子注量率分别为1.67×10⁹、2.44×10⁷和3.03×10⁶ cm^-2•s^-1。以上结果达到了BNCT设计要求,并能满足瞬发γ测量血硼浓度的要求。     

拉曼光谱内标法定量分析Purex有机体系中的U(Ⅵ)

本工作研究了Purex后处理流程模拟有机料液中U(Ⅵ)的定量分析方法。首先扣除硝酸铀酰有机溶液拉曼光谱的荧光背景,并以30%TBP/煤油位于1 065cm-1处的特征峰为内标峰,将U(Ⅵ)位于860cm-1处对称伸缩振动峰(ν1)强度与内标峰强度的比值,对铀浓度绘制标准曲线,在U(Ⅵ)质量浓度为5.0~107.0g/L范围内,标准曲线为y=0.063 6x+0.357,r2=0.999。经过内标法处理后的标准曲线具有更好的稳定性,75d后相对强度标准曲线为y=0.062 4x+0.489,r2=0.999。F检验与t检验证明,在显著性水平α=0.05时,两条标准曲线在分析精度与斜率上无显著性差异。使用内标法后,可透过容器壁直接分析铀浓度,容器对检测结果的影响较小,5种容器对U(Ⅵ)检测影响相对误差均不高于3.7%,故检测过程无需进行样品的转移及分装,简化了实验步骤。经内标法修正后,改变拉曼光谱仪的积分时间和激光功率基本不影响U(Ⅵ)的定量检测,从而可选择合适的参数以适应不同浓度U(Ⅵ)溶液分析的需要。     

铀(Ⅵ)和三辛基氧化膦配合物在离子液体中的电化学与光谱性质

选择具有代表性的中性含磷萃取剂三辛基氧化膦（TOPO）作为配体,考察其与高氯酸铀酰在疏水离子液体［N₄₁₁₁］［NTf₂］中形成配合物的光谱和电化学行为。该配合物在离子液体中的紫外 可见吸收光谱呈现出峰间距为(728±9)cm^-1的电子振动带系,其红外光谱中铀酰离子不对称伸缩振动频率（ν_as）为926cm^-1。电化学研究显示,［UO₂(TOPO)₄］²⁺的电极还原过程由两个连续的单电子还原过程组成,对应的还原峰电位分别为E_pc1=-1.37V和E_pc2=-1.75V（vs. Ag⁺/Ag）,其中前者为准可逆,后者不可逆。该U(Ⅵ)→U(Ⅴ)准可逆过程的半波电位E_1/2=-1.33V,不随扫描速率和温度改变,说明该过程可逆性较好,且还原产物稳定。该配合物的扩散活化能为E_a=(39.0±1.1)kJ/mol。该体系可能在以离子液体为介质的电化学分离过程中具有潜在的应用前景。     

Optical path design of phase contrast imaging on HL-2A tokamak

A phase contrast imaging(PCI) diagnostic has recently been developed on HL-2 A tokamak. It can diagnose plasma density fluctuations with maximum wave number of 15 cm~(-1) and wave number resolution of 2 cm~(-1). The time resolution reaches 2 μs. A 10.6 μm CO_2 laser is expanded to a beam with a diameter of 30 mm and injected into the plasma as an incident beam,injecting into plasma. The emerging scattered and unscattered beams are contrasted by a phase plate. The ideas of optical path design are presented in this paper, together with the parameters of the main optical components. The whole optical path of PCI is not only carefully designed, but also constructed on HL-2 A. First calibration results show the ability of this system to catch plasma turbulence in a wide frequency domain.     

Angular dependence of the sputtering yield from a cylindrical track

The dependence of the sputtering yield on the incident angle, Θ, is determined using molecular dynamics (MD) simulations for a cylindrical track produced by a fast ion. For a ‘small' spike radius and for the mean energy in the track, E_exc, smaller than the binding energy, U, a (cosΘ)^−1.7 dependence is found, close to the linear collision cascade (LCC) result and to some thermal spike models. On the other hand, when E_exc>U, the incident angle dependence is (cosΘ)⁻¹. For a larger spike radius we obtain a (cosΘ)^−1.6 dependence for both high and low energy densities. Analytic spike models based on diffusive transport are shown not to give satisfactory results. In addition, at low energy densities we see correlated atom ejection ignored in analytic models. Applying the MD results to the experimental data for electronic sputtering of solid O₂ at large excitation densities suggests that the effective spike radius is larger than the initial Bohr adiabatic radius indicating that energy is rapidly transported from the initially narrow track.     

基于Si-PIN探测器的电流型计数式α粒子测量

为解决基于Si-PIN探测器的传统计数型粒子测量系统在测量低强度脉冲辐射场时存在的计数率低和不能直接测量粒子时间信息的问题,提出了电流型计数测量方法。其原理是对电流型Si-PIN探测器在粒子入射时输出的脉冲信号进行线性放大和高速数字化,并使用数字信号处理算法进行数据分析以获得粒子测量信息。利用电流型Si-PIN探测器、电流型前置放大器和高带宽数字示波器组建了电流型计数测量系统,并在241 Am-244 Cm和239 Pu源上开展了α粒子测量实验。实现了脉冲幅度谱和粒子入射时间的联合测量,同时利用FIR及IIR型数字滤波器改善了能谱测量的能量分辨率。系统的最大计数率达2×106 s-1,适用于低强度脉冲辐射场测量。     

Influence of high-voltage pulse parameters on the propagation of a plasma synthetic jet

In this work, a typical pin-to-pin plasma synthetic jet in static air is excited by a pulsed DC power supply. The influences of the pulse rising time, the amplitude and the repetition frequency of the pulse voltage on the jet flow have been investigated. First, using a high-speed Schlieren imaging technique, the induced shock waves and the fast jet flow generated by the plasma synthetic jet are characterized. With a deposited energy of 44 mJ per pulse, the velocity of the shock wave and the maximum velocity of the jet flow reach 320 m s⁻¹ and 100 m s⁻¹, respectively. Second, when the applied voltage increases from 12.8 kV to 16 kV, the maximum jet velocity increases from 66 m s⁻¹ to 93 m s⁻¹. On the other hand, as the pulse rising time varies from 50 ns to 500 ns, or the pulse repetition frequency increases from 5 Hz to 40 Hz, the jet velocity induced by the plasma synthetic jet is weakly dependent. In addition, a comparative study of the plasma synthetic jets using three commercial pulsed power supplies (XJ-15, NPG- 18, and PG-30) is implemented. It reveals that the maximum jet velocity of 120 m s⁻¹ is obtained in the case of PG-30, with the longest pulse rising time and the lowest breakdown voltage, while the maximum velocity of 33 m s⁻¹ is detected in the case of NPG-18, even though it has the shortest pulse rising time and the highest breakdown voltage.