共查询到20条相似文献，搜索用时 62 毫秒
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报道了利用兰州重离子加速器国家实验室ECR离子源引出的全裸Ar15 离子与Be和Mo固体表面相互作用产生的X射线实验测量结果。结果发现,同样条件下,对于较重的靶原子容易激发其外壳层特征X射线,产额很高。 相似文献
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综述了低能高电荷态Ar^q＋离子与不同金属表面相互作用时,入射粒子和靶原子发射的X射线谱研究。重点分析了q=16时,高电荷态Ar^16＋离子与金属表面相互作用过程中发射Ar的Kα特征X射线的机理,以及q=17,18时入射粒子单粒子X射线产额等问题。分析总结了核电荷数不同的金属靶原子受激发射X射线的机理,以及入射离子的动能跟靶原子X射线产额的关系。展望了预期的研究方向。 相似文献
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《物理教学探讨》2005,23(15)
1914年--劳厄劳厄(Max Theodor Felix Von Laue,1879-1960)因发现X射线在晶体中的衍射获得了1914年的诺贝尔物理学奖。自从1895年伦琴发现X射线以来,关于X射线的本质,科学家们提出了各自的看法。劳厄认为,X射线是电磁波。他在与博士研究生厄瓦耳交谈时,产生了用X射线照射晶体以研究固体结构的想法。他设想,X射线是极短的电磁波,而晶体是原子(离子)的有规则的三维排列。只要X射线的波长和晶体中原子(离子)的间距具有相同的数量级,那么当用X射线照射晶体时就应能观察到干涉现象。在劳厄的鼓励下,索末菲的助教弗里德里奇和伦琴的博士研究… 相似文献
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研究了高电荷态离子129Xe29 入射金属Au表面产生的X射线谱。分析结果表明,足够高的电荷态低速离子激发靶表面原子,无需很强的束流强度,便可有效地产生重原子的特征X谱线(Au-Mα),特征X射线的幅度和产额随入射离子的动能的增加而增加。 相似文献
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《物理教学探讨》2005,23(17)
1917年——巴克拉巴克拉(CharlesGloverBarkla,1877-1944)因发现元素的次级X射线标识谱获得了1917年度诺贝尔物理学奖。当X射线照射到固体、液体或气体上时,都会引起两种完全不同的次级辐射:其一是微粒辐射,即电子发射;其二是次级X射线辐射。巴克拉对次级X射线辐射的本质作了最重要的和最详细的研究。他首先发现了次级X射线辐射存在两种不同的X射线:其中一种X射线的吸收系数、穿透本领等性质和入射X射线的相同,被认为是散射后的原X射线。这种散射后的X射线的强度随相对于入射X射线方向的不同而变化。通过对这种X射线强度分布的测量,巴… 相似文献
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在重离子与靶原子直接碰撞导致原子内壳层空穴产额与离子入射动能关系的基础上,计算了单离子入射引起的原子间碰撞产生的原子内壳层空穴产额。给出了低能重离子与靶原子碰撞过程,原子内壳层X射线单离子产额与离子动能的关系。较好地解释了动能300~600 ke V的Xe^27＋离子入射Mo靶,激发的Mo的L X射线的实验结果。 相似文献
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“X射线”又称伦琴射线,它是一种波长很短的电磁辐射.波长越短的X射线能量越大,叫做硬X射线,波长长的X射线能量较低,称为软X射线.当在真空中,高速运动的电子轰击金属靶时,靶就放出X射线,放出的X射线分为两类:如果被靶阻挡的电子的能量不越过一定限度时,只发射连续光谱的辐射,这 相似文献
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普通物理的光学教材中,关于X射线在晶体上的衍射的条件,在讨论中都没有明确给出,而且说法还存在侧重面不同的差异。例如,“劳厄的伦琴衍射花样的每一亮点看做是伦琴射线对晶体每一点阵平面组的相干性反射所导致的结果。……把粒子（也可以用粒子间严格有规律的对应点）看做是相干次波的中心”①;“每一个晶胞,都作为基元衍射中心来处理,这个基元衍射中心和光学光栅上的狭缝相对应”②;“处在格点上的原子或离子其内部的电子在外来电磁场的作用下,做受迫振动,成为一个新的波源,向各个方向发射电磁波。也就是说,在X射线的照射下,晶体中的每个格点成为一个散射中心。这些散射中心在空间周期性地排列,它们发射的电磁波频率与外来X射线的频率相同,而且这些散射波是彼此相干的,将在空间发生干涉”③。 相似文献
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《海外英语》2007,(5):10-11
Many college freshmen arrive woefully unprepared to do college work, and as disadvantaged populations continue to grow, the share of the American work force that has made it through college is expected to plummet. Many experts blame that educational failure not just on high schools but also on colleges. School & College, a special report by The Chronicle, looks at efforts to fix the system. What reforms would better prepare students for college? What should schools and colleges be doing differently? How should state and federal officials help? 相似文献
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罗艳萍 《读与写:教育教学刊》2008,5(6)
The communication of people partially is the communication of cultures. Culture has a direct effect on international commercial activities in all aspects. Different conceptions about time, space, equality, law and the like, lead people to deal with things in different ways. So to know cultures of the counterpart is to facil-itate our enterprises so as to have a smooth and successful communication in commercial activity. 相似文献
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《海外英语》2007,(4):36
There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love. 相似文献
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Migration occurs behind a variety of reasons and has a great effect on the whole world. People may migrate in order to improve their economic situation, or in order to escape civil strife, persecution, and environmental disasters. The impact of migration is complex, bringing both benefits anddisadvantages. This paper briefly talks about the causes of migration, the allocation of benefits, and the ways in which individual countries and the international community deal with this important subject. 相似文献
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Richard Denner 《海外英语》2007,(4):14-15
Rosco and I wait for the fishermen to return.I sit at a wooden bench near the store at Mt.Baker Resort and watch the clouds change shape. Rosco has my belt around his neck and an eight foot tow chain hooked to a tree. Dogs must be on a leash. Ducks and rabbits are loose. 相似文献
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Given a graph G,a subgraph C is called a clique of G if C is a complete subgraph of G maximal under inclusion and |C|≥2. A clique-transversal set S of G is a set of vertices of G such that S meets all cliques of G. The clique-transversal number, denoted as TC (G), is the minimum cardinality of a clique-transversal set in G. The clique-graph of G, denoted as K (G), is the graph obtained by taking the cliques of G as vertices, and two vertices are adjacent if and only if the corresponding cliques in G have nonempty intersection. Let F be a class of graphs G such that F={G|K(G) is a tree}. In this paper the graphs in F having independent clique-transversal sets are shown and thus TC (G)/|G|≤1/2 for all G ∈ F. 相似文献
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Sister Carrie is one of the most controversial characters in American literature.Thought as a "fallen woman" firstly,she was defined as a "new woman" by some critics later. However, by digging into the motivaton behind the whole process of Carrie's "success", the relationship between Carrie and her creator (the author), the social conditions of then American, it can be found that Carrie has never been free-standing on her thought and she has never found her real-sdf even after becoming a famous actress. In a society dominated by mass consumerism Carrie is only an adherent of her own desires. She also is a representative of all those country girls flooded into cities, a symbol and a sacrifice of the urbanization of America in a time countryside was overcome by cities. 相似文献