低能高电荷态氮离子与Cu表面相互作用致K-X射线发射的研究

利用中国科学院近代物理研究所的电子回旋共振离子源引出的高电荷态氮离子(N^q+,q=3,5,6),在4.5～120 keV动能范围内系统测量了N^q+(q=3,5,6)与Cu表面碰撞产生的K-X射线能谱;基于原子壳层电离理论计算了K-X射线产额值及其电离截面值。结果表明:N^q+(q=3,5)离子进入靶表面后与Cu原子发生紧密碰撞,在直接库伦电离的作用下发射K-X射线,并且随着入射离子动能的增加,K-X射线产额和K壳层电离截面均单调增大;对于N⁶⁺离子,K-X射线产额与其入射动能没有明显的依赖关系,且在Cu表面形成的"空心原子"级联退激产生的K-X射线产额约占其总K-X射线产额的97%。另外,N⁵⁺离子入射时的K-X射线产额明显高于N³⁺离子入射时的产额。本工作对离子与表面相互作用中形成的"空心原子"的退激过程具有重要的参考价值,并为理解"空心原子"的退激过程和彗星X射线机理的研究提供了基础数据。     

低能Xe离子辐照在Al表面上的光辐射研究

本文测量了200~550 keV的Xe10+离子轰击高纯度（9999%）Al表面诱发的溅射Al原子的光发射,研究了Al Ⅰ 30810、30914、39452、39628 nm光谱线强度比值和光子产额随入射离子能量的变化趋势。在本实验能量范围内,辐射光谱线强度比值随入射离子能量增加几乎不变,而发射谱线的光子产额随入射离子能量的增加呈现出不同趋势：入射离子能量为450 keV时,光子产额出现极大值,入射离子能量超过450 keV时,光子产额随能量的增加而减少,其变化趋势与核阻止本领随能量增加的变化没有出现类同的变化特征。结合核阻止和电子阻止效应对实验结果进行了讨论,结果表明：入射离子能量低于450 keV时,核阻止在碰撞中起主导作用,入射离子能量高于450 keV时,电子阻止在碰撞中起主导作用。     

核乳胶在激光直接驱动内爆DT燃料离子温度诊断中应用

在神光Ⅱ基频光直接驱动内爆实验中，采用国产核乳胶测量了DD反应产生的质子产额，根据DD反应的质子产额与DT反应的中子产额的比值，诊断了DT燃料离子温度；由于核乳胶对质子的探测效率比中子探测效率高，产额比值法在低产额特别是间接驱动实验条件下诊断燃料离子温度是一种较好的方法。     

MeV能量Si~+引起二次离子发射的研究

利用北京大学2×1.7 MV串列加速器终端的飞行时间(TOF)谱仪,分别用1.5、2.0和3.0MeV三种能量的初级束Si+轰击样品来研究其二次离子发射现象,使用的样品包括石墨、碳纳米管等。结果表明,采用合理的降噪方法后得到了高信噪比和高时间分辨率的二次离子质谱,实现了全质量范围无遗漏记谱。利用H-C12峰刻度之后,计算得出二次离子各成分的最可能构成及产额,碳纳米管样品表面氢质量含量为8.15%。同时,发现MeV能区二次离子产额与Si+阻止本领之间的关系并非简单的正相关。     

离子溅射对氚钛靶寿命的影响

应用TRIM程序模拟了离子在氚钛靶上的溅射产额。结果显示,O+、N+、C+和D+2等在氚钛靶上的溅射是导致氚钛靶寿命下降的重要因素。为了减小离子溅射对氚钛靶寿命的影响,束流入射角应小于45°。     

MeV离子轰击碳样品引起的碳氢团簇产额

利用北京大学2×1.7MV静电串列加速器产生的1.5MeV Au2+和Si+束流轰击碳纳米管样品,用二次离子飞行时间质谱方法分析了二次离子成分,通过质量已知的样品的定标,确认了轰击产生的二次离子质量。分析束流轰击后的二次离子产额,发现在此能量下二次离子产额与离子在物质中射程的横向歧离表现出正相关。     

低能离子与脱氧腺苷酸组分水溶液作用合成脱氧腺苷酸

利用气体常压弧光放电产生低能离子,以低能N^ 注入D－2－脱氧核糖,磷酸二氢铵的腺嘌呤水溶液,用高效液相色谱,核磁共振等方法对反应产物进行分析,证明有5－脱氧腺苷酸生成,给出了产物的产额－时间曲线,并对反应机理作了初步探讨。     

高压气体电离室中离子漂移速度的实验测量

提出了一种在高气压下电离室离子漂移速度的测量方法,进行了理论分析,搭建了实验测量系统。利用DDC112电流积分放大器对充有4MPa氙气的高压气体电离室输出电流脉冲信号分别进行等间隔积分时间和步进积分时间采集测量,根据理论分析对测量数据分别进行二次和三次曲线拟合。通过拟合曲线系数间的比例关系计算出离子漂移时间,根据电离室结构和工作条件计算出4MPa氙气中氙离子迁移率为0.0181~0.0196cm²•V^－1•s^－1,并外推计算出0.1MPa氙气中氙离子迁移率为0.72~0.78cm²•V^－1•s^－1,与文献资料中的测量结果一致。     

AVLIS离子引出收集过程的初步研究

通过理论计算研究了１－Ｄ无碰撞ＡＶＬＩＳ离子引出过程，比较了交变场与恒定场对离子引出特性的影响，计算和分析结果表明等离子体离子密度≥１０７ｃｍ（－３），屏蔽效应存在，离子的引出在振荡中完成；对相同离子密度，随电场的增加，离子引出时间有饱和趋势，比较了脉冲场与恒定场的引出效果，结论是两者的引出效果一样，而采用脉冲场可消除斯塔克效应的影响。     

离子初始速度对等离子体鞘层厚度的影响

本文从理论上研究了离子初始速度对等离子体鞘层厚度的影响,建立了理论计算公式和数值模拟方法,考察了离子初始速度对鞘层厚度的影响因子。在离子初始能量为3.2 eV情况下,用粒子模拟程序进行了数值模拟,模拟与理论计算得到的空间电场分布十分接近。     

Separation of the alpha-emitting radioisotopes actinium-225 and bismuth-213 from thorium-229 using alpha recoil methods

An innovative method has been demonstrated for separating alpha-emitting isotopes for medical radiotherapy applications. The method relies on recoil-ion separation rather than on conventional wet chemistry techniques to separate medical isotopes from their precursor sources. The isotopes ²²⁵Ac and ²¹³Bi have been separated from electro-deposited sources of ²²⁹ThO₂. Separations of ²²⁵Ac were carried out by placing nickel recoil collector foils in firm contact with the ²²⁹ThO₂ sources. One-stage recoil-ion separations of ²²⁵Ac from ²²⁹Th have been performed as well as two-stage separations of ²¹³Bi from previously recoil separated ²²⁵Ac. In addition, a direct recoil separation of ²¹³Bi from ²²⁹Th has been demonstrated. The ²¹³Bi from the one-stage direct separation has a high isotopic purity, but contains small amounts of long-lived ²²⁵Ac alpha activity. The two-stage separations of ²¹³Bi produce high isotopic purity material (>99.9999%), but result in lower isotopic yields. Range-energy calculations have been carried out to determine the yields of recoil ions as a function of alpha-particle energy and ThO₂ thickness. The results of the calculations have been benchmarked with recoil separation measurements carried out using ThO₂ electro-deposits over a range of thickness. A computer code based on the generalized Bateman equations has been developed to allow calculations of the amounts of any isotope in the ²²⁹Th decay chain as a function of recoil separation exposure time and elapsed time after the separation. An excellent match has been obtained between the predictions of the Bateman calculations and the results of recoil separation measurements. The recoil separation method has proven to be a simple and effective way of separating medically useful isotopes such as ²¹³Bi. In addition, the method has been shown to produce no chemical or radioactive wastes, in contrast to radiochemical separation methods, which generate mixed (chemical and radioactive) waste.     

Computer simulation of transmission sputtering of thin films and experimental measurements of recoil implantation of gold into silicon

Transmission sputtering of thin (up to 300 Å) gold films bombarded by 10 to 20 keV Ar ions is simulated by using the MARLOWE computer code. The energy spectra, angle of ejection and depth of origin distributions of ejected particles are presented. The results indicate that even for a thin film the cascading of the recoils is sufficient to produce an E^?2 energy spectrum and a cosine angular distribution. The evaluated transmission-sputtering yields for various film thicknesses are compared with the amount of gold retained in a silicon substrate in dynamic recoil mixing experiments.     

Sputtering mechanisms near the threshold energy

Threshold energies for sputtering cannot be calculated directly but have to be evaluated from the energy dependence of the sputtering yields. This paper investigates trajectories of projectile and recoils near the threshold energy for sputtering, where the collision cascade becomes increasingly simple. Statistics of the different collision events show which processes dominate the sputtering close to the threshold energy for selfbombardment of different light and heavy targets. The differential cross-sections for scattering and recoil production explain qualitatively the probability for the various processes.     

Structure dependent electronic sputtering of a-C:H films by swift heavy ions

Electronic sputtering of a-C:H films by elastic recoil detection analysis technique is studied under 80 MeV Ni⁸⁺ and 150 MeV Ag¹³⁺ ion irradiations. These studies show that electronic sputtering yield of C and H from the films varies with film structure quite significantly. The structure of the films is analyzed from the characteristic graphitic (G) and disordered (D) modes of Raman vibration. Atomic force microscopy was performed on two films for grain size determination. The difference in electronic sputtering yields is discussed on the basis of structural influence of the films on swift heavy ion and solid interaction.     

An Experimental Apparatus for Low Energy High Charge Heavy Ions to Study Collisions on Atomic Hydrogen

The design and performance of a recoil ion source system which includes a recoil ion source, atomic hydrogen thermal oven target and an electrostatic analysis system will be discussed. The recoil ion source produces low velocity highly charged ions via collisions between heavy fast pump beams from the EN tandem accelerator and target gases. Time-of-flight techniques provide initial recoil charge state separation. Collisions of the recoils with atomic hydrogen are being studied. The atomic hydrogen is provided by a thermal oven which features long life time operation and low input power requirements. Dissociation fractions of 80% are achieved for 300 watts of input power. A hemispherical electrostatic analyzer allows the final charge states of the recoil ions to be determined thereby allowing the measurement of charge exchange processes for an energy range of 100 eV/q to 5000 eV/q for the incident recoil ions.     

Measurement of 4He-p recoil cross sections

The recoil cross sections of protons induced by ⁴He⁺ particles were experimentally determined in an energy range of 1.3–2.1 MeV at recoil angles of 20° and 30 ° . The angular dependence of the recoil cross section at 2.0 MeV was also measured. By using the principle of detailed balance, a calculation of ⁴He-p recoil cross sections were calculated from p-⁴He phase shift data. Good agreement between the experimental data and theoretical values was found. The results show that recoil cross sections at low energies are non-Rutherford and are larger than the Rutherford value by approximately a factor of 2 at 2.0 MeV.     

FNS-100正比计数器用于测量快中子场能谱时的干扰分析

为了了解FNS-100正比计数器用于测量快中子场能谱时干扰信号的特性,本文计算分析了60Co产生的低能γ射线以及7 MeV和10 MeV的高能γ射线所产生的干扰,同时模拟了反冲3He核、反冲质子在该正比计数器中产生的干扰影响.计算结果表明,γ射线对快中子能谱测量几乎没有影响,而反冲3He核和反冲质子存在比较大的影响.     

Secondary particle yield and energy release data from intranuclear-cascade-evaporation model calculations of high energy (20–1100 MeV) neutron interaction with elements of shielding and biological importance

Secondary particle (neutron, proton, pion and heavy ion) yields and energy release data for 20, 50, 100, 300, 500, 800 and 1100 MeV neutron collisions with H, C, N, O, Al, Si, Ca, Fe and Pb have been calculated using the intranuclear-cascade-evaporation model. The low-energy limit is discussed and compared with the ENDF/B-IV neutron data. The mean elastic recoil energies have also been estimated by means of the Ranft formula for angular distribution. The multigroup response functions (kerma factors and production cross-sections) have been obtained and applied calculating the energy deposition and particle yields in the deep-penetrated graphite and iron spheres. The results for energy deposition of the ANISN neutron transport code using a high energy cross-section library and the derived kermas are about 10% overestimated relative to the thick-target results from the high energy particle transport code HETC. In the neutron transport discrete ordinates calculation the secondary production is underestimated when comparing with the HETC code.     

氡子体α能谱真空测量RaB的反冲损失率

氡子体α能谱法测量时的真空度使RaB发生反冲损失,这会对氡子体测量精度产生影响并造成测量腔室的污染。本实验选用0.8 μm孔径的Millipore AA型滤膜,在流率为6.3、12.3和15.6 L/min下,使用ELPI粒径分析仪、α测量仪和α谱仪分别对氡室气溶胶粒径分布、滤膜自吸收系数及反冲损失率进行测量。结果显示：氡室内气溶胶浓度呈单峰分布;相应流率下的自吸收系数为0.978、0.980、0.989,反冲损失率为0.362 8、0.368 4和0.362 9;所得反冲损失率并未表现出较大的差异,但滤膜样品上由RaA衰变产生的RaB原子却有较大的反冲损失。