北京大学4.5 MV静电加速器核反应分析系统

为满足对聚变堆面向等离子体材料中氘氚滞留问题的研究,北京大学4.5 MV静电加速器在原束线基础上新增核反应分析系统,该系统使用能量0.8～3.6 MeV的H~+、D~+、~3He~+和~4He~+粒子束流,可对核反应微分截面和样品中元素浓度的深度分布进行测量分析。本文对核反应分析原理、核反应分析系统的设备布局和实验方法进行了讨论,并以D(~3He,p)~4He核反应为例,分析了微分截面计算和样品中氘元素浓度深度分布的数据结果,其深度分辨小于1.5μm,实验误差约为7.5%。     

高温He离子辐照引起的Hastelloy N合金微结构变化研究

本文采用30 keV的He离子辐照Hastelloy N合金,辐照温度为500C,剂量分别为:1×10¹⁵、×10¹⁵、1×10¹⁶He⁺/cm²。利用扫描电子显微镜（SEM）研究了辐照后块体样品的表面形貌。结果表明,辐照后的块体样品均观察到了表面起泡现象。利用透射电子显微镜（TEM）研究了辐照后TEM样品微结构的变化。结果表明,低剂量(1×10¹⁵ He⁺/cm²)辐照的样品中出现了黑斑缺陷;随着辐照剂量的增加,开始出现位错环及纳米级的氦泡,同时黑斑密度减少;当剂量增至1×10¹⁶He⁺/cm²,位错环以及氦泡的尺寸和密度明显增大,晶界处氦泡更加密集。     

200 MeV以下光子诱发50,51V核反应数据理论计算

光核反应数据在辐射损伤、反应堆剂量、加速器屏蔽等方面有重要应用。本工作基于MEND-G程序,对200 MeV能量范围内光子诱发^50,51V核反应数据进行理论计算,给出包含中子、质子、⁴He等主要出射粒子的核反应的数据;对光子诱发V同位素核反应的实验测量进行自洽性分析,结合光子强度函数和准氘模型,将光核反应吸收截面计算能力提升到200 MeV,为光核反应理论计算提供数据基础。经系统比对,理论计算值与实验测量值一致性很好,数据收录在即将发布的CENDL-3.2光核子数据库中。     

基于双核模型研究大质量转移反应中结团发射机制

本文借助双核模型，进行了对多核子转移反应中前平衡结团发射机制进行了系统研究。以反应系统¹²C+²⁰⁹Bi、⁴⁰Ca+²⁰⁸Pb和⁴⁸Ca+²³⁸U为例，重点分析了库仑位垒附近重离子碰撞产生前平衡轻粒子，如中子、质子、氘核、氚核、³He、⁴He、⁶Li、⁷Li、⁸Be和⁹Be时间演化、动能分布和角分布。研究结果表明：结团发射呈现出一定核结构效应，⁴He发射概率与质子相当并远大于³He。前平衡结团主要分布在“类弹”和“类靶”角度区域发射，其动能分布呈现出玻尔兹曼分布形式。考虑结团预形成因子后该方法可以拓展用于不稳定原子核引起的结团发射机制研究。     

贮氚非晶态锆钒合金膜中的氦释放行为

用热解吸和静态贮存方法对贮氚非晶态ZrV₂合金膜中³He的释放行为进行了系统分析。结果显示：³He原子存在597.3、725.8和1 146.6 K等3个解吸峰,其中第3解吸峰的解吸量最大,是由非晶态基体中的³He释放形成;在长达2 423 d的静态贮存期间,非晶膜中³He原子的释放系数始终在10^-5量级范围内波动并呈线性上升趋势,但仍未加速释放;贮存温度变化会引起释放系数剧烈波动;与贮氚晶态ZrV₂合金膜相比,非晶膜的固氦能力显著增强。上述结果初步证实了非晶合金具有良好的固氦性能,这有助于人们从全新视角认识材料中的氦行为。     

氘-氘聚变反应高能γ射线产额的实验研究

本文对低能D(d,γ)⁴He聚变反应进行了实验研究。由于D(d,γ)⁴He聚变反应γ射线的产额低、能量高、本底大,实验采用大NaI-塑料闪烁体反康谱仪,以提高探测效率并降低宇宙线的影响;采用脉冲束飞行时间方法区分中子和γ射线,以减小中子和宇宙线本底的影响。实验测量了300 keV d束轰击厚D靶和薄D靶两种情况下的γ数据。在计算反应产生23.8 MeV的高能γ峰面积时,采用了拟合法扣除本底。实验测得,对厚靶,D(d,γ)⁴He反应截面为2.47×10^-37m²;对薄靶,D(d,γ)⁴He反应截面为4.36×10^-37m²。     

强碱性阴离子交换树脂用于90YCl3溶液金属杂质的纯化

从⁹⁰Sr/⁹⁰Y放射性衰变平衡体系中分离获得的90Y溶液具有无载体、金属杂质含量高等特点,需要进一步纯化才能应用于⁹⁰Y放射性药物的制备。本工作研究了AE4强碱性阴离子交换树脂在盐酸溶液中对Y³⁺、Fe³⁺、Al³⁺、Zn²⁺、Mg²⁺的吸附性能。结果表明：AE4树脂在盐酸溶液中不吸附Al³⁺、Zn²⁺、Mg²⁺;在3 mol/L以上的盐酸溶液中对Fe³⁺吸附性能较好;在7 mol/L以上的盐酸溶液中对Y³⁺的吸附性能较好。含有Y³⁺、Al³⁺、Zn²⁺、Mg²⁺等元素的混合溶液在3 mol/L HCl溶液通过AE4树脂柱后,Fe³⁺基本被全部吸附在树脂柱上;吸附余液调节盐酸浓度至7 mol/L,通过另一根AE4树脂柱,Y³⁺基本被吸附在树脂柱上。最后用0.01 mol/L HCl洗脱吸附在树脂柱上的Y³⁺,得到纯化后的YCl₃溶液。稳定核素和90Y示踪的研究结果表明,采用AE4树脂纯化⁹⁰YCl₃溶液的工艺可行,AE4树脂可用于90YCl3溶液中Fe、Al、Zn、Mg等主要杂质金属元素的去除。     

D+注入Li4SiO4的表面化学状态及其热解吸行为

锂陶瓷氚增殖剂的氢同位素行为是聚变堆固态产氚包层关心的重要课题。本文将3 keV D⁺注入Li₄SiO₄,采用X射线光电子能谱在线分析注氘前后材料表面的化学状态,同时采用热解吸谱（TDS）实验技术,研究注氘后Li₄SiO₄中氢同位素的热解吸行为。实验结果表明：D⁺注入会改变Li₄SiO₄表面的化学环境,产生多种辐照缺陷和化学键合状态;氘滞留量和热解行为受注氘时样品的温度影响较大,可在一定程度上预测产氚包层中氚的滞留行为。     

低能核反应及相关核结构研究进展

中国原子能科学研究院核反应团队依托国内外的大科学装置，在重离子熔合-裂变机制、垒下熔合增强机制、奇特核反应机制、奇异结构和奇异衰变方面取得了多项原创性成果。本文对其中的代表性成果进行了简要回顾。主要包括(：1)系统调查了正Q值中子转移的耦合道效应，并提出了自洽的方法评估转移耦合的贡献，发现了异常的同位素效应；(2)提出了用高精度背角准弹散射方法抽取原子核的形变参数，确证了原子核存在十六极形变；(3)提出了用轻带电粒子的替代俘获反应方法，基于此方法给出了关键的²³⁹Pu(n,2n)反应截面；(4)系统考察了sd壳丰质子核奇异衰变谱学，发现了²²Si的β缓发双质子衰变模式，并发现镜像核²²Si/²²O的β衰变中存在极大的同位旋不对称性，同时在²⁶Si中发现了迄今为止最强的同位旋混合态(；5)系统研究了奇特核体系在近垒能区的反应机制，首次给出了实验证据表明经典色散关系不适用于中子晕核⁶He+²⁰⁹Bi体系，并对质子滴线核⁸     

北京市气溶胶放射性核素分析(2013—2016)

利用中国锦屏地下实验室(CJPL)低本底γ谱仪对北京地区近4年34组气溶胶样品中长寿命放射性核素进行研究。发现气溶胶样品中含有²³⁸U、²²⁶Ra、²¹⁰Pb、²³²Th、²²⁸Ra、 ⁴⁰K、⁷Be、¹³⁷Cs,其活度浓度均值分别为17.47 μBq·m^-3、21.19 μBq·m^-3、2.39 mBq·m^-3、11.12 μBq·m^-3、14.43 μBq·m^-3、226.64 μBq·m^-3、6.98 mBq·m^-3、2.36 μBq·m^-3,且均在本底范围之内。同时,放射性核素活度浓度与环境参数存在相关性,⁷Be、⁴⁰K、¹³⁷Cs、²²⁶Ra均与季节负相关,²¹⁰Pb与季节正相关;⁴⁰K与空气质量指数(AQI)正相关。     

Depth-profiling of beryllium on graphite with ion beams

The surface layer of beryllium-coated graphite was analysed by backscattering and nuclear reaction methods using a 2.5 MeV accelerator. For the Be analysis the nuclear reactions ⁹Be(p, d)⁸Be, ⁹Be(p, )⁶Li, ⁹Be(d, p)¹⁰Be, ⁹Be(d, t)⁸Be, ⁹Be(d, )⁷Li and ⁹Be(³He, p)¹¹B are compared with backscattering of ⁴He⁺ and protons. For the analysis of carbon, which provides complementary information to the depth profiling of Be, and for the analysis of oxygen, which is the third element of importance in the system, elastic backscattering of ⁴He⁺ and protons is applied. It turns out that the backscattering analysis with protons of 1.3 MeV presents the best compromise for a quick and straightforward measurement of all three elements. The other methods have their merits for a more detailed analysis.     

3D hydrogen profiling by elastic recoil detection analysis in transmission geometry

An analytical procedure and a simulation-optimization algorithm are described for hydrogen determination based on elastic recoil detection induced by low-energy ⁴He ions ( 3 MeV) using transmission geometry. Hydrogen concentration depth profiles can be derived from the experimental recoil spectra for a depth range of up to 6 μm with a resolution better than 40 nm at the surface. The method is applied to thin polyimide films irradiated by high-energy heavy ions. The 3D hydrogen distribution is determined with a ⁴He⁺ mubeam. A high-hydrogen-concentration zone below the surface is shown. The hydrogen distribution is seen to evolve during the ⁴He⁺ irradiation.     

Investigations of lattice location and mobility of carbon in GaAs using the channeling technique

In order to get information about the lattice location and the mobility of ¹²C in GaAs wafers, the channeling technique in combination with nuclear reaction analysis (NRA) is a powerful method. The targets were implanted with ¹²C ions (2.6 × 10¹³−2.6 × 10¹⁵cm⁻²) at energies between 60 and 3000 keV. This corresponds to implantation depths of about 0.1 to 3 μm. Using the nuclear reaction ¹²C(d, p)¹³C a depth distribution of the implanted carbon is obtained. The relationship between the concentration of ¹⁴C in random and along the 100 and 110 axial directions gives information about the substitutional lattice location of carbon within the GaAs crystal. In addition, we measured lattice defect depth distributions with a 1.5 MeV ⁴He⁺ beam before and after thermal annealing at temperatures up to 600°C.     

Determination of the electronic energy loss of light ions in a silicon lattice by using the transmission ion channeling method

Charged particle activation analysis (CPAA) is able to analyze light elements such as carbon and oxygen at trace levels in semiconductor materials. This technique requires the knowledge of the stopping powers of these materials for channeled ions. The electronic energy loss for ions entering the crystal lattice in a random direction is well established. The electronic energy losses for protons, deuterons, ³He⁺ and ⁴He⁺ ions entering a 3.6 μm thick silicon single crystal along the 1 0 0 direction were measured by using the transmission of particles technique. Data obtained were compared with those obtained by other authors using theoretical and experimental methods.     

脉冲离子束作用下金属氚化物氦释放测量技术研究

为认识脉冲离子束作用下金属氚化物的氦释放行为,建立了脉冲离子束作用下金属氚化物氦释放测量系统。利用标准体积气体取样装置,采用气体反扩散法,对系统的容积比、灵敏度进行了实验标定。在此基础上,发展了脉冲离子束作用下金属氚化物氦释放的测量技术,开展了脉冲离子束作用下金属氚化物氦释放实验研究。结果显示,单次脉冲离子束作用下金属氚化物的氦释放呈脉冲式,释放量最大可达10~(13)个原子以上。     

用转移反应研究6He奇特核体系的光学势

由于受到放射性束强度弱、品质差的限制,奇特核体系的光学势性质一直是亟待解决的国际难题。本工作利用稳定束的转移反应作为探针,深入研究了反应出射道奇特核体系的光学势性质。利用中国原子能科学研究院的HI-13串列加速器在近库仑位垒能区高精度测量了⁷Li+⁶³Cu、²⁰⁸Pb的弹性散射以及单质子转移反应角分布,并利用扭曲波玻恩近似（DWBA）和耦合反应道（CRC）方法对实验数据进行了拟合,抽取了出射道⁶He+⁶⁴Zn、²⁰⁹Bi晕核体系的光学势参数。所得参数可重现文献中已有的6He体系的弹性散射角分布,验证了这种方法的可靠性。对所得势参数的能量相依性的分析表明,在重体系⁶He+²⁰⁹Bi中,基于因果律的色散关系并不适用,其潜在的物理原因还需进一步深入研究。     

The cross section for the K(n,p)Ar reaction between 14.2 and 17.2 MeV

Activation techniques have been used to measure the cross section for the ⁴¹K(n,p)⁴¹Ar reaction between 14.2 and 17.2 MeV. Neutrons were produced by the ³H(d,n)⁴He reaction, and the mixed-power method was used to measure the neutron flux through the ²⁷Al(n,)²⁴Na reaction. The activated samples were counted for the 1294 keV, 1.827 h γ-activity of ⁴¹Ar and the 1369 keV, 15.03 h γ-activity of ²⁴Na using a 16% Ge(Li) detector and a 4096-channel analyzer. The cross sections for the ⁴¹K(n,p)⁴¹Ar reaction using the mixed-power method were found to be 53 ± 3 mbarn at 14.2 ± 0.2 MeV, 47 ± 3 mbarn at 15.2 ± 0.2 MeV, 41 ± 3 mbarn at 16.2 ± 0.2 MeV and 36 ± 4 mbarn at 17.2 ± 0.2 MeV. The associated-particle method was also used for measuring the neutron flux in order to check the mixed-powder result at 14.2 MeV. The average cross section for three associated-particle runs at 14.2 MeV was found to be 50 ± 3 mbarn which, within experimental error, agrees with the mixed-powder value.     

Damage production in GaAs during MeV ion implantation

The influence of the nuclear and electronic energy loss on the damage production in GaAs has been studied by Se⁺ ion implantation at T_I = 293 K with energies ranging from 2 MeV up to 20 MeV. The ion dose was varied between 5 × 10¹² /cm² and 1 × 10¹⁵ /cm². The damage production was investigated using RBS in channeling regime. Temperature and energy dependent backscattering measurements and TEM investigations were performed to study the kind of defects in more detail. The resulting defect profiles are compared with the depth distribution of the nuclear and electronic energy loss which were simulated by TRIM 87. The results show that the remaining defect concentration strongly decreases with increasing implantation energy even if the same energy density is deposited into nuclear processes. We suppose, that the electronic energy loss increases the defect transformation and annealing during implantation at T_I = 293 K. The defects in the samples implanted with energies greater than 5 MeV are characterized as point defects, point defect clusters and small dislocation loops; the kind of defects are the same over the whole implantation depth and the existence of amorphous zones can be widely excluded.