灰岩侵蚀速率的研究

测定不同地貌环境下的侵蚀速率是了解地表形成及演化的基础。目前,已有人用10Be/26Al双核素和宇宙成因核素36Cl来研究灰岩表面的侵蚀速率和暴露年龄。本工作通过36Cl的AMS测量计算了北京地区灰岩表面的侵蚀速率,其结果为(1.33±0.28)×10-5m.a-1。     

Be掺杂纤锌矿ZnO电子结构的第一性原理研究

采用密度泛函理论结合投影缀加波方法,对Be掺杂导致ZnO禁带宽度增加的机理进行了研究.通过对掺杂前后电子能带结构、总态密度以及分态密度的计算和比较,发现导带底(CBM)是由Be 2s电子与Zn 4s电子共同控制;而Be_xZn_1-xO价带顶 (VBM)始终由O 2p电子占据.随着掺杂量的增加,决定带隙宽度的CBM的位置上升,同时VBM的位置下降,从而导致了带隙的变宽,出现了蓝移现象.此外,Be掺杂会使晶胞发生压缩,这种压应变也是导致Be 关键词： 密度泛函理论 电子结构 Be掺杂ZnO     

厚靶低中能9Be(d,xn)反应加速器中子源特性研究

利用PHITS程序评价计算了厚靶9Be(d, xn)反应加速器中子源的能谱和角分布数据，重点讨论了JQMD、INCL和INCL/DWBA三种核反应物理模型计算厚靶9Be(d, xn)反应中子辐射场分布的适用性。研究结果显示，基于INCL/DWBA耦合模型的PHITS程序计算所得到的厚靶9Be(d, xn)反应中子能谱和角分布数据能够较好地与实验数据符合，可以为厚靶9Be(d, xn)反应中子源特性研究及应用提供较为准确的中子辐射场数据。此外，设计了水冷大面积旋转铍靶的方案，并在5~25 MeV/5 mA入射氘能量下条件下，开展了靶面温度模拟研究，结果显示，靶面最高温度可控制在100 oC以下。     

轻奇特核结构中的核心激发--以11Be为例

近年来,越来越多的实验表明,很多轻奇特核结构中都有核心激发成分。本研究以丰中子晕核11Be为例,介绍核心激发成分的实验和理论研究进展,重点阐述核心激发成分对直接核反应微分截面的影响。实验上,1n移除反应及11Be（p,d）和10Be（d,p）转移反应是测量11Be核心激发成分比例的典型实验类型。理论上,发展了能够包括11Be核心激发成分的Faddeev AGS方法,XDWBA方法以及XCDCC方法。加入核心激发成分后,这些模型的计算结果可以更加合理地描述11Be在各种靶上的弹性散射和碎裂微分截面。通过对比是否包含核心激发成分的计算结果,发现其影响主要体现在弹散微分截面的大质心系角度,以及（p,d）转移反应角分布的小质心系角度。另外,对E_x=0:5s3 MeV的激发能区的碎裂反应,核心激发的影响不可忽略;对E_x=3s5:5 MeV的碎裂反应,核心激发的贡献非常重要。It was found that many light exotic nuclei have the core-excitation components. In this paper, taking one-neutron halo nucleus 11Be for example, the experimental and theoretical research progress, as well as the influences on the direct nuclear reaction differential cross sections of this exotic component were reviewed. The 1n removal, 11Be(p, d) and 10Be(d, p) transfer reactions are typical experimental methods to investigate this component. The Faddeev AGS, the XDWBA, and the XCDCC methods are developed to include this constituent in various theoretical models. With the core-excitation component, the calculated results can more reasonably describe the elastic scattering and breakup differential cross sections of 11Be impinging on various targets. Comparing the full XCDCC calculation with that omitting core-excitation effect, we found that this component mainly affects the elastic scattering differential cross sections at large center-of-mass angles, and the (p, d) transfer reaction angular distributions at small center-of-mass angles. In addition, its effect is non-negligible for the breakup reaction within the excitation energy interval of E_x = 0:5~3 MeV, and is remarkable for E_x =3 5:5 MeV.     

7Be在Pd和Au中衰变率变化的相对测量

将HI-13串列加速器次级束流线产生的放射性核素7Be分别注入到Pd和Au中,利用两个高纯锗探测器同时测量7Be EC衰变核素7Li第一激发态放出的478 keV γ射线产额随时间的变化,发现7Be在Pd中的衰变率比在Au中大(0.8±0.2)%,并讨论了衰变率差别与这两种材料的电子亲合势及有效电子密度的关系.     

Be, O共掺杂实现p型AlN的第一性原理研究

基于密度泛函理论框架下的第一性原理平面波超软赝势方法,研究了掺杂和非掺杂AlN体系的晶格参数、 能带结构、总体态密度、分波态密度、差分电荷分布及电荷集居数.计算结果表明: Be掺杂AlN晶体能够在能隙中形成深受主能级,空穴载流子局域于价带顶, 而引入了激活施主O原子的Be, O共掺杂方法,能使受主能带变宽、非局域化特征明显. 同时,受主能级向低能方向移动,形成了浅受主能级, 从而提高了Be原子的掺杂浓度和系统的稳定性. Be, O共掺杂更有利于获得p型AlN.     

Be薄膜应力的X射线掠入射侧倾法分析

由于铍薄膜极易被X射线穿透, 传统的几何模式下很难获得有效的X射线衍射应力分析结果. 本文采用掠入射侧倾法分析SiO₂基底上Be薄膜残余应力, 相比其他衍射几何方法, 提高了衍射的信噪比, 获得的薄膜应力拟合曲线线形较好. 对Be薄膜的不同晶面分析, 残余应力结果相同, 表明其力学性质各向同性; 利用不同掠入射角下X射线的穿透深度不同, 获得应力在深度方向上的分布; 由薄膜面内不同方向的残余应力相同, 确定薄膜处于等双轴应力状态. 关键词： Be薄膜 X射线衍射 应力     

太阳核心中7Be电子俘获几率的计算

在太阳核心的条件下 ,7Be原子被完全电离 .所以 ,重新计算的7Be和8B太阳中微子流强分别约为 4 0 0× 1 0 9cm- 2 ·s- 1和 6 1 8× 1 0 6 cm- 2 ·s- 1,而标准太阳模型预言的7Be和8B太阳中微子流强则分别是 4 80× 1 0 9cm- 2 ·s- 1和 5 1 5×1 0 6 cm- 2 ·s- 1.这将进一步增大在SuperKamiokande太阳中微子实验上中微子流强的实验测量值与理论预计值之间的差异 .     

Preliminary study of ~(10)Be/~7Be in rainwater from Xi'an by Accelerator Mass Spectrometry

The ~(10)Be/~7Be ratio is a sensitive tracer for the study of atmospheric transport, particularly with regard to stratosphere-troposphere exchange. Measurements with high accuracy and efficiency are crucial to ~7Be and ~(10)Be tracer studies. This article describes sample preparation procedures and analytical benchmarks for ~7Be and ~(10)Be measurements at the Xi'an Accelerator Mass Spectrometry(Xi'an-AMS) laboratory for the study of rainwater samples. We describe a sample preparation procedure to fabricate beryllium oxide(Be O) AMS targets that includes co-precipitation, anion exchange column separation and purification. We then provide details for the AMS measurement of ~7Be and ~(10)Be following the sequence BeO~-→Be~(2+)→Be~(4+) in the Xi'an- AMS. The ~(10)Be/~7Be ratio of rainwater collected in Xi'an is shown to be about 1.3 at the time of rainfall. The virtue of the method described here is that both ~7Be and ~(10)Be are measured in the same sample, and it is suitable for routine analysis of large numbers of rainwater samples by AMS.     

Be,C双受主共掺杂实现P型AlN的第一性原理研究

基于密度泛函理论(Density Functional Theory)的第一性原理平面波超软赝势方法(USPP),首先对Be、C掺杂Al N的晶格结构进行优化,得到其稳定结构.然后对Be、C掺杂Al N的晶格参数、结合能、能带结构、电子态密度和电荷集居数进行了详细地计算和分析.计算结果表明:Be-2C共掺杂Al N的构型具有更稳定的结构,能使受主能级变宽、非局域化特征明显.因此,Be-2C共掺杂Al N有望成为一种更稳定高效的p型掺杂手段.     

An experimental study of the 9Be(p, π+)10Be and 9Be(p, π−)10C reactions at 185 MeV

A magnetic spectrometer was used for the momentum analysis of pions produced by 185 MeV protons on a ⁹Be target. The obtained energy resolution (0.55 MeV FWHM) made it possible to resolve a number of discrete final states in ¹⁰Be and ¹⁰C. Energy spectra were measured in the angular region 15°–130° (lab). Angular distributions for six peaks in ¹⁰Be and four peaks in ¹⁰C are presented in tables and graphs. A peak corresponding to a not previously reported level in ¹⁰Be was observed at 11.75 ±0.11 MeV excitation energy. The measured $\text{π}{}^{\mathrm{+}}\text{π}{}^{\mathrm{?}}$ ratio for the ground state analogues was found to be angular dependent and varied from 30 at 35° (lab) to 2 at 125° (lab). The results are compared with theoretical predictions and discussed in terms of one- and two-nucleon models.     

Electromagnetic properties of 7Li and 7Be in a cluster model

The electromagnetic properties of ⁷Li (⁷Be) are studied by using a microscopic α-t (³He) cluster model. Among the several properties are the Coulomb and magnetic form factors for the ground spin-doublet states of ⁷Li (⁷Be), density distribution radii, static moments and radiative transition probabilities. Provided that the stability conditions for the binding energies are satisfied for both the constituent nuclei α and t (³He), the calculated results are in good agreement with many available data. Several interesting differences are predicted between ⁷Li and ⁷Be.     

A microscopical DWBA description of the charge-exchange reactions (7Li, 7Be)

The charge-exchange reaction (⁷Li, ⁷Be is described in the frame of a microscopical DWBA with central effective forces. The transition density for ⁷Li-⁷Be is calculated in two ways: with a one-particle model and with a cluster model, taking full account of recoil effects. The formalism is used for the cases of (⁷Li, ⁷Be reactions with ⁶Li and ⁴⁰Ca. Further cross sections for reactions on ¹²C and ¹⁶O with $\text{E(}{}^7\text{Li) = 78 MeV}$ and excitation energies around 4.5 and 6.2 MeV, respectively, are compared to new data obtained at the Kurchatov Institute. Here particle-hole states in an oscillator model were used to characterize the heavy system. Angular distributions are well reproduced, but absolute cross sections are 6–7 times too small. This indicates that the assumption of a direct one-step process is correct, but that tensor forces should be included as a component of the effective nucleon-nucleon force.     

The 12C(18O, α)26Mg and 12C(18O, 8Be)22Ne reaction

Excitation functions for α-emission leading to the ground and first excited states of ²⁶Mg and ⁸Be emission leading to the ground and first and second excited states of ²²Ne have been measured at several forward angles for E_c.m. = 15 to 22.4 MeV. There is little evidence for correlated structure. The angular distribution at 16.5 MeV for the α + ²⁶Mg(g.s.) channel is rather structureless while that for the ⁸Be+²²Ne(g.s.) channel appears to be dominated by a J = 13 contribution. Statistical model calculations indicate that much of the yield for both the α and ⁸Be exit channel is compound nuclear in origin, with some indication of a larger direct contribution for the ⁸Be channel at the lower end of the bombarding energy range.     

Proton scattering from 9Be between 6 and 30 MeV and the structure of 9Be

Differential cross-section excitation functions at lab scattering angles 86.9°, 120.0°, 140.0° and 160.0° were measured for ⁹Be(p, p_o)⁹Be, ⁹Be(p, p₂)⁹Be and ⁹Be(p, d₀)⁸Be at proton lab energies from 6 to 15 MeV in 100 keV steps. A broad anomaly was observed in the ⁹Be(p, p₀)⁹Be excitation functions. Differential cross-section angular distributions were measured for ⁹Be(p, p₀)⁹Be and ⁹Be(p, p₂)⁹Be at lab energies of 13.0, 14.0, 15.0, 21.35 and 30.3 MeV and for ⁹Be(p, d₀)⁸Be at 13.0, 14.0, 15.0 and 21.35 MeV. Angular distributions of polarization analysing powers for ⁹Be($\text{p}$,p₀)⁹Be, ⁹Be(p, p₂)⁹Be and ⁹Be($\text{p}$, d₀)⁸Be were measured at 8.0, 11.0, 12.0, 13.0 and 15.0 MeV. A spherical optical-model (SOM) analysis of the elastic scattering angular distribution data from 13.0 to 30.3 MeV showed that an energy dependence of only V_R and W_s (volume real and surface imaginary depths) is sufficient to reproduce the measurements. Coupled-channels (CC) analyses were made with a quadrupole-deformed optical-model potential and strong coupling of $\text{3}\text{2}{}^{\mathrm{?}}$, $\text{5}\text{2}{}^{\mathrm{?}}$ and $\text{7}\text{2}{}^{\mathrm{?}}$ levels of a $\text{K =}\text{3}\text{2}$ ground-state rotational band of ⁹Be. The ⁹Be(p, p₀)⁹Be and ⁹Be(p, p₂)⁹Be data from 13.0 to 30.3 MeV were analyzed simultaneously at each energy, varying only V_R and W_s with energy, for a potential deformation of β = 1.1. Both SOM and CC analyses indicated the same energy dependence in V_R, while W_s averaged 3.5 MeV lower in CC than in SOM, with both energy dependences consistent with previous analyses of nucleon scattering from 1p shell nuclei.     

The 12C(9Be,n)20Ne reaction

A study of the ¹²C(⁹Be, n)²⁰Ne reaction has been carried out at bombarding energies of 16 and 24 MeV. The spectra at both incident energies are dominated by a consistent set of levels between an excitation energy of 7.3 ± 0.4 and 15.7 ± 0.3 MeV. The rotational band based on the K^π = 0₃⁺ state appears to be strongly populated. Based on this selectivity, additional evidence is provided in favor of identification of the 8⁺ state at 15.9 MeV with this 0₃⁺ band. Angular distributions measured at the higher bombarding energy are compared with statistical compound-nuclear calculations. It appears that a non-statistical mechanism is responsible for the reaction's selective population of states with 8p-4h configuration. Such a mechanism, involving the preferential breakup of the ⁹Be into ⁸Be plus a neutron, is discussed.     

Elastic scattering of 9Be on light target nuclei

The elastic scattering of ⁹Be on the target nuclei ⁹Be, ¹²C, ¹³C and ¹⁶O was measured at projectile energies of 14, 20 and 26 MeV. All angular distributions show a diffraction-like structure. In addition, excitation curves were measured for the scattering of ⁹Be on ⁹Be at three different angles in the energy range of 9–22 MeV. An optical potential having parameters independent of mass number and energy and reproducing all the measured angular distributions in the forward angular region was found and compared with that for the scattering of ⁹Be on medium and heavy nuclei.     

12C1 and 8Be production in 12C + 208Pb collisions

The mechanisms involved in the production of fast α-particles in ¹²C-induced reactions have been studied for the ¹²C + ²⁰⁸Pb system at the bombarding energies of E_12c = 132, 187 and 230 MeV. Absolute cross sections for the reactions ²⁰⁸Pb(¹²C. ¹²C¹→α + ⁸Be), ²⁰⁸Pb(¹²C, ⁸Be(g.s.)) and ²⁰⁸Pb(¹²C, ⁸Be(2.94 MeV)) have been determined by coincidence measurement of two or three correlated α-particles. Inclusive α-particle production cross sections were also measured at E_12c = 187 MeV. It is found that the inelastic process (¹²C, ¹²C¹→α + ⁸Be) does not contribute significantly to fast α-particle production but that the production of ⁸Be by projectile fragmentation is an important source of α-particles. At the highest bombarding energy (230 MeV) it appears that the ¹²C → 3α fragmentation reaction becomes more prominent at the expense of the ¹²C→α + ⁸Be fragmentation channel.     

Study of 11B at high excitations with the 9Be(3He,p)11B and 9Be(α, d)11B reactions

The nucleus ¹¹B has been studied over the excitation energy range from 8.5 MeV to 21.5 MeV with the ⁹Be(³He, p)¹¹B / reaction at / E_{³He = 38 MeV}. The analogs of the parent states in ¹¹Be have been located at 12.56, 12.92, 14.40, 16.44, 17.69, 18.0, 19.15 and 21.27 MeV. A complementary measurement with the ⁹Be(α, d)¹¹B reaction at E_α = 48 MeV demonstrates that the 16.44, 17.69, 18.0 and 19.15 MeV resonances have rather pure isospin $\text{T}{}_{\mathrm{f}}\text{=}\text{3}\text{2}$. The 14.40 MeV state is a strongly isospin-mixed analog of the $\text{5}\text{2}{}^{\mathrm{+}}\text{1.78}\text{MeV}$ state in ¹¹Be. It is argued that spin S = 1 transfer is involved in the excitation of the 16.44 MeV state and its 3.887 MeV parent in ¹¹Be in a two-step stripping process. The $\text{T}{}_{\mathrm{f}}\text{=}\text{1}\text{2}$ states and the lowest three $\text{T}{}_{\mathrm{f}}\text{=}\text{3}\text{2}$ states are compared with the predictions of DWBA utilizing shell-model form factors. It is concluded that the $\text{T}{}_{\mathrm{f}}\text{=}\text{1}\text{2}$ strength is more strongly fragmented than is implied by the calculations of Teeters and Kurath.     

Low-energy cross section for 6Li(d,n)7Be

Cross sections were determined for the ⁶Li(d, n)⁷Be reaction between 100 and 180 keV deuteron energy using the activation method. Different methods of extrapolation were employed and compared down to the energy region of astrophysical interest.