Absolute number of scintillation photons in liquid xenon byalpha-particles

To apply scintillation material to radiation detectors, a quantity such as the W-value, defined as an average energy expended per ion-pair in gaseous detectors, must be determined experimentally. The authors define the effective W_S-value as E ₀/N_p an average energy dissipated to emit a scintillation photon, if the energy of radiation E_o is completely absorbed in material and the number of scintillation photons N_p are emitted. They have attempted to determine N_p in liquid xenon due to alpha-particles with an energy of 5.303 MeV from ²¹⁰Po to estimate W_S for scintillation in liquid xenon. The absolute scintillation yield was obtained as 3.26×10⁵ for alpha-particles for 5.303 MeV in liquid xenon. This result followed from fitting the absolute photo-electron yields measured with a VUV sensitive photomultiplier, which was used as a photodiode, to the results of Monte Carlo simulation     

Self-calibrating position-sensitive silicon detectors

Position-sensitive silicon detectors with discrete position output signal levels, which have been developed for heavy ion reaction studies at the Lawrence Berkeley Laboratory are discussed. The detectors, both 300- and 5000-μm thick, for use in ΔE-E telescopes, use a series of high and low conductivity strips on the detector p⁺ contact to produce a position signal with 15 discrete levels. Since the position of the signals from the strips is known, the detectors are self-calibrating against position nonlinearities. Some aspects of the fabrication of both the 300- and 5000-μm detectors are discussed, along with their operating characteristics. Illustrative experimental results of ¹³⁹La-induced reactions on ⁴⁰Ca targets are presented     

Some characteristics of the crystalline-amorphous threshold pointof 31P+ ion-implanted silicon substrates

During ion implantation a stage can be reached in which a continuous layer within the implanted crystal changes into amorphous material. The change begins when the implanted dose attains a certain threshold value (D_T). In-situ reflectivity (R) versus dose (D) measurements, made during the implantation of ³¹P⁺ into Si single crystal substrates showing that both D_T and the work (W_oT) required to induce the threshold conditions within the implanted crystal increase with the implantation energy are reported. It is also shown that the change in reflectivity ΔR_i, which occurs in the dose range that contains D_T, is a function of E and peaks at 140 keV, the energy at which the damaged layer becomes buried. The ratio D_A/D_T is found to be a decreasing function of E     

LiCl-KCl熔盐中钍的电极过程研究

通过循环伏安法和计时电位法,研究LiCl-KCl熔盐中Th⁴⁺在723～803 K内在Mo电极上的电极过程。结果表明,Th⁴⁺在Mo电极上的电极过程受离子扩散步骤控制,扩散系数D随温度T变化的经验公式为ln D＝33.94-2.879×10⁴/T,形式电位的经验公式为E _vsCl-^0′/Cl²＝-3.45+7.5×10^-4T。     

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     

腐殖酸对Re(Ⅶ)在高庙子膨润土中扩散的影响研究

腐殖酸是环境中普遍存在的一种有机物,它能通过络合作用和氧化还原反应影响放射性核素的迁移。本文通过贯穿扩散实验,在不同膨润土密度和不同腐殖酸接触时间下,研究了Re(Ⅶ)在高庙子膨润土中的扩散,得到了有效扩散系数De和容量因子α。结果显示,随着膨润土密度从1 600kg/m3增加至1 800kg/m3,De从1.8×10-11 m2/s减小至0.59×10-11 m2/s。随着腐殖酸接触时间由0d增加到60d,De由0.59×10-11 m2/s增大至0.83×10-11 m2/s。实验得到的α值均小于总孔隙率,说明在腐殖酸存在的条件下,Re(Ⅶ)可能仍以阴离子的形态在膨润土中扩散。     

HNO3介质中U(Ⅳ)还原Np(Ⅴ)的动力学

采用分光光度法研究了HNO₃溶液中U(Ⅳ)还原Np(Ⅴ)的反应,获得了动力学方程-dc (Np(Ⅴ))/dt=kc(Np(Ⅴ))c^0.7 (U(Ⅳ))c^1.9 (H⁺)c (NO^-₃),25℃时反应速率常数k=(6.37±0.49)×10^-3 L^3.6/(mol 3.6•min),反应活化能E_a=60.13 kJ/mol。结果表明,浓度为0~4.2×10^-2mol/L的U(Ⅵ) 对U(Ⅳ)还原Np(Ⅴ)的反应几乎没有影响,并探讨了可能的反应机理。     

材料中氢同位素行为热脱附谱实验方法研究

材料中氢同位素行为研究是确保聚变堆安全和经济性的关键问题和重要研究方向。为研究材料中氢同位素的扩散、释放、居留等特性,建立了一种联合四极质谱仪（QMS）的热脱附谱（TDS）实验方法,解决了TDS系统超高真空、低氢同位素质谱本底、线性升温速率控制以及灵敏度标定等关键科学技术问题。通过涡轮分子泵和二级溅射离子泵实现了优于1×10^-7Pa的超高真空,本底H₂分压降至1×10^-9Pa。通过MCGS直流PID控温程序实现样品升温速率在1～100 K/min范围可调,采用漏率可变的特制通导型玻璃漏孔标定TDS系统的氘气脱附速率灵敏度,确定该灵敏度系数α和最小可检测氘气热脱附速率（脱附速率灵敏度）分别为6.22×10²⁴s^-1·A^-1、1.24×10^-10s^-1。采用镀镍Zr-4合金吸氘样品验证了TDS方法的有效性,初步分析了Zr-4中的氘热脱附特性。     

人造岩石固化体SrCeTi2O7的合成与性能研究

采用⁸⁸Sr模拟放射性核素⁹⁰Sr,Ce⁴⁺模拟四价锕系放射性核素。以分析纯SrCO₃、CeO₂和TiO₂为主要原料,通过高温固相反应制备SrCeTi₂O₇人造岩石固化体。对固化体的烧成工艺、物理性能、晶体结构及微观形貌进行研究,并对固化体的热稳定性及抗浸出性能进行探讨。结果表明,选择配方n(SrCO₃)∶n(CeO₂)∶n(TiO₂)＝1∶1∶2,在1 450 ℃下保温5 h可合成结构致密、晶型发育完整的SrCeTi₂O₇人造岩石固化体;Dicvol程序指标化结果表明,该固化体化合物属四方晶系,晶胞参数为a＝0.387 33(4) nm,c＝0.388 07(5) nm;SrCeTi₂O₇人造岩石固化体具有良好的热稳定性,经高达800 ℃热处理后样品仍保持原有物相不变;PCT-B粉末浸泡法测试结果表明,SrCeTi₂O₇人造岩石固化体具有较好的抗浸出性能,浸泡周期28 d时Sr、Ce和Ti的浸出率分别为3.51×10^-4、8.23×10^-8和2.02×10^-7 g/(m²·d)。     

Compton recoil electron tracking with silicon strip detectors

The application of silicon strip detectors to Compton gamma ray astronomy telescopes is described. The silicon Compton recoil telescope tracks Compton recoil electrons in silicon strip converters to provide an unique direction for Compton scattered gamma rays above 1 MeV. With strip detectors of modest positional and energy resolutions, of 1 mm FWHM and 3% at 662 keV, respectively, true imaging can be achieved to provide an order of magnitude improvement in sensitivity to 1.6×10 ^-6 γ/cm²-s at 2 MeV. The results of extensive Monte Carlo calculations of recoil electrons traversing multiple layers of 200 μm silicon wafers are presented. Multiple Coulomb scattering of the recoil electron in the silicon wafer of the Compton interaction and the next adjacent wafer is the basic limitation to determining the electron's initial direction     

氨基羟基脲与Np(Ⅵ)的还原动力学

研究了氨基羟基脲(HSC)浓度、H~+浓度、NO_3~-浓度、Fe3+浓度、UO2+2浓度、反应温度对氨基羟基脲与Np(Ⅵ)还原反应速率的影响,获得了其动力学方程。实验结果表明:增加氨基羟基脲浓度和提高反应温度,降低H~+浓度和NO_3~-浓度,可以提高氨基羟基脲与Np(Ⅵ)还原速率;在UO2+2存在或Fe3+浓度小于1×10-3 mol/L时,对氨基羟基脲与Np(Ⅵ)的还原没有明显影响。氨基羟基脲还原Np(Ⅵ)的动力学方程式为:-dc(Np(Ⅵ))/dt=kc(Np(Ⅵ))c2.52(HSC)c-0.53(H+)c-0.61(NO_3~-),在4.00℃时k=(1 037±60)(mol/L)-1.40·s-1,活化能Ea=(64.03±6.4)kJ/mol。     

30%TBP-煤油-HNO3体系的α辐解行为Ⅰ.溶剂辐解生成DBP/MBP的规律

用气相色谱法研究了²³⁸Pu为α源的30%TBP-煤油-HNO₃体系的辐解产物DBP和MBP的生成情况,研究了反萃剂、反萃条件和钚等因素对DBP/MBP分析的影响,考察了辐照累积剂量、剂量率和稀释剂等因素对DBP和MBP生成量的影响。结果表明：DBP和MBP生成量随吸收剂量、剂量率的增加而增大;在剂量率73.7Gy/min、累积剂量5×10⁵Gy时,DBP浓度达到7.09×10^-2mol/L,MBP浓度达到9.84×10^-3mol/L;在吸收剂量5×10⁵Gy时,加氢煤油、正十二烷和特种煤油中的DBP生成量分别为4.45×10^-2、4.44×10^-2 、4.35×10^-2mol/L,MBP生成量为3.52×10^-3、3.50×10^-3、3.52×10^-3mol/L,在吸收剂量5×10⁵Gy时,三种稀释剂的DBP和MBP的生成量近似相等;在吸收剂量5×10⁴Gy时,α辐照的DBP和MBP的生成量分别为5.57×10^-2mol/L和5.10×10^-3mol/L,对应的γ辐照的为2.50 ×10^-3mol/L和3.14×10^-4mol/L,α辐照产生的DBP和MBP的生成量明显大于γ辐照的。     

Development of a helicon-wave excited plasma facility with high magnetic field for plasma-wall interactions studies

The high magnetic field helicon experiment system is a helicon wave plasma(HWP)source device in a high axial magnetic field(B_0)developed for plasma–wall interactions studies for fusion reactors.This HWP was realized at low pressure(5?×?10~(-3)?-?10 Pa)and a RF(radio frequency,13.56 MHz)power(maximum power of 2 k W)using an internal right helical antenna(5 cm in diameter by 18 cm long)with a maximum B_0of 6300 G.Ar HWP with electron density~10~(18)–10~(20)m~(-3)and electron temperature~4–7 e V was produced at high B_0 of 5100 G,with an RF power of 1500 W.Maximum Ar~+ion flux of 7.8?×?10~(23)m~(-2)s~(-1)with a bright blue core plasma was obtained at a high B_0 of 2700 G and an RF power of 1500 W without bias.Plasma energy and mass spectrometer studies indicate that Ar~+ion-beams of 40.1 eV are formed,which are supersonic(~3.1c_s).The effect of Ar HWP discharge cleaning on the wall conditioning are investigated by using the mass spectrometry.And the consequent plasma parameters will result in favorable wall conditioning with a removal rate of 1.1?×?10~(24)N_2/m~2 h.     

High-energy-density electron beam generation in ultra intense laser-plasma interaction

By using a two-dimensional particle-in-cell simulation,we demonstrate a scheme for highenergy-density electron beam generation by irradiating an ultra intense laser pulse onto an aluminum(Al) target.With the laser having a peak intensity of 4?×?1023W cm~(-2),a high quality electron beam with a maximum density of 117 ncand a kinetic energy density up to8.79?×?1018J m~(-3) is generated.The temperature of the electron beam can be 416 Me V,and the beam divergence is only 7.25°.As the laser peak intensity increases(e.g.,1024 W cm~(-2)),both the beam energy density(3.56?×?1019J m~(-3)) and the temperature(545 Me V) are increased,and the beam collimation is well controlled.The maximum density of the electron beam can even reach 180 nc.Such beams should have potential applications in the areas of antiparticle generation,laboratory astrophysics,etc.     

Scintillation properties of RbGd2Br7:Ce.Advantages and limitations

The scintillation properties of RbGd₂Br₇ crystals, doped with Ce³⁺ concentrations of 0.02, 0.11, 0.88, 2.05, 4.1, and 9.8%, are studied under X-ray and γ-quanta excitations. For the RbGd₂Br₇ sample doped with 9.8% Ce, the authors measured a light yield of 56000±6000 photons per MeV of absorbed γ-ray energy with a main decay time of 43±1 ns, using a Hamamatsu R1791 photomultiplier (PMT), a ¹³⁷Cs radioactive source, and a shaping time of 10 μs. A time resolution of 790±10 ps was measured for the RbGd₂Br₇:9.8% Ce compound, using BaF₂ as second scintillator, two XP2020Q PMTs, a ²²Na source, and an energy threshold set at E⩾511 keV. With the R1791 PMT, an energy resolution of 4.1% (FWHM over peak position) for the 662-keV full absorption peak has been observed for two crystals of 7×4×2 mm³ and 15×5×1 mm³ with 4.1 and 9.8% Ce content, respectively. Moreover, the nonproportional responses of three RbGd₂Br₇:Ce compounds with different concentrations (0.11, 2.05, and 9.8%) were studied revealing an almost-constant light output response from 17.4 keV to 1 MeV. These properties are compared to three other well-known scintillators: NaI:Tl, CsI:Tl, and Lu₂SiO₅:Ce     

LiH和LiT与H2O反应机理研究

氢材料在微量H₂O、CO₂、O₂和N₂存在下可能发生物理化学反应,使材料的物理品位下降。由于反应过程十分复杂,很难从实验上准确获取这类反应的最佳通道和具体产物信息,因此,从理论上研究氢材料分子的物理化学性质及其化学反应机制,了解化学反应过程具有十分重要的意义。本文使用Gaussian03软件包和Gaussview工具软件,在6-311G(d)全电子基函数水平上,应用二阶微扰理论优化得到了⁶LiH、⁶LiT与H₂O反应的中间体、过渡态及产物的结构,总能量,振动频率和零点能等。通过计算发现⁶LiH、⁶LiT均只有1个反应通道,⁶LiH与H₂O反应的焓变、活化能和反应速率常数分别为-156.99 kJ/mol、8.95 kJ/mol和3.75×10¹⁰(mol•dm^-3)^-1/s,⁶LiT与H₂O反应的焓变、活化能和反应速率常数分别为-159.02 kJ/mol、9.92 kJ/mol和1.72×10¹⁰ (mol•dm^-3)^-1/s。     

Am在两种不同地下水中的种态分布及溶解度分析

利用自主编写的地球化学计算软件CHEMSPEC分析了Am在北山地下水和我国西南某地下水中的种态分布,并计算了Am在这两种地下水中的溶解度,考察了pH、Eh、不同离子以及硅的存在等对种态分布的影响。结果表明,Am在这两种地下水中均以正三价存在,随pH值的不同Am的种态会发生较大的变化,在偏酸性条件下,主要以AmSO+4、Am(SO4)-2及Am3+的形式存在,在中性至弱碱性条件下,以AmCO+3的形式存在,强碱性条件下,则基本转化为Am(OH)3;当北山地下水中有Si存在时,在pH=6.5~9.7范围内,Am的主要种态为AmSiO(OH)2+3;不同离子的浓度变化对Am的种态分布会产生一定影响,其影响顺序为HCO-3F-SO2-4Cl-。pH和HCO-3对Am溶解度的影响较大,随着地下水pH的升高,Am的溶解度逐渐减小。Am在两种地下水中的溶解度分别为2.01×10-7 mol/L(北山地下水pH=7.56、Eh=164mV)、1.60×10-7 mol/L(西南地下水pH=7.50、Eh=0mV)。     

用于同位素电池的储能复合电极的可行性研究

借鉴太阳能电池Ti/Pd/Ag复合电极的设计方案,将其优化设计为Ti/Pd/Au复合电极并加载氚源,以此验证同位素源与换能器件整合的可行性。在N型单晶硅基体上制备电极,为研究氚在电极中的行为,用氘气模拟氚气对电极进行同位素加载,采用XRD、SEM和四探针研究复合电极的储氚性能、微结构、电学性能等的变化。结果表明：复合电极能吸附氘并生成TiD_x（x≤2）,具备一定的储氚性能;在Ti与Si界面处出现了TiSi₂相,表明膜基间发生了合金化,这提高了复合电极与硅基体的结合强度,同时降低了接触电阻;10^-4 Ω•cm量级的表面电阻率基本可满足对电极导电性能的要求。由此可见,Ti/Pd/Au复合电极应用于伏特效应同位素电池是可行的。     

电沉积 LEU UO2 靶件生产医用99Mo的工艺研究

⁹⁹Mo是一种重要的医用放射性同位素。采用低浓铀（LEU）靶件生产裂变⁹⁹Mo是发展趋势。本工作进行了电沉积UO₂靶件制备、靶件溶解以及⁹⁹Mo化学分离等工艺研究,确定了电沉积LEU UO₂靶件制备医用裂变⁹⁹Mo的工艺流程。研究表明,于不锈钢管内壁上电沉积UO₂,在pH=7、电流0.5~2 mA/cm²、温度75~90 ℃、镀液中U浓度5 mg/mL条件下,经过约210 h电沉积,不锈钢管内壁上UO₂沉积层质量达到42 mg/cm²;采用6 mol/L HNO₃溶解UO₂镀层。采用α-安息香肟沉淀法实现⁹⁹Mo与大量裂变产物的初步分离,采用阴离子交换法与活性炭色层法联用实现⁹⁹Mo的纯化;纯化后的⁹⁹Mo溶液中,杂质¹³¹I、⁹⁰Sr、⁹⁵Zr、¹⁰³Ru、²³⁸U活度与⁹⁹Mo活度比值分别为4.47×10^-6%、7.40×10^-7%、8.67×10^-7%、2.57×10^-6%、1.69×10^-14%,均小于《欧洲药典》规定值,满足医用要求。本工作建立了电沉积LEU UO₂靶件生产高纯医用裂变⁹⁹Mo的工艺流程,为今后采用LEU技术生产医用裂变⁹⁹Mo,进而实现其自主规模化生产打下了基础。     

硝酸体系中铂催化肼还原U(Ⅵ)的反应动力学

开展了硝酸体系中以肼为还原剂、铂黑为催化剂催化还原U(Ⅵ)的动力学研究。通过考察U(Ⅵ)浓度、肼浓度、酸度以及催化剂用量等条件对反应过程的影响,确定了反应的初始动力学速率方程为-dc(UO²⁺₂)dt=kc^0.44(UO²⁺₂)c^0.19(N₂H⁺₅)c^-0.23(H⁺),在60 ℃、固液比r_S/L=2.0 g/L时,速率常数k=2.6×10^-3 (mol/L)^0.6/min。研究了温度对反应速率的影响,结果表明,在20~75 ℃范围内,随着温度升高,反应速率加快,反应过程由动力学控制转变为扩散控制过程。对比了硝酸体系与高氯酸体系的反应动力学实验数据,发现相同条件下硝酸体系的反应速率明显低于高氯酸体系,并分析了其中的原因。