Radiative Double Electron Capture (RDEC) of Ions with Quasi-Free Electrons

准自由电子离子的辐射双电子捕获 (RDEC)

• 批准号: 1401429
• 负责人: John Tanis
• 金额: $ 13.35万
• 依托单位: Western Michigan University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-10-01 至 2017-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1401429&HistoricalAwards=false
• 关键词: Radiative; Double; Electron; Capture; RDEC

Non-technical description:This project involves an investigation of how two of the smallest and most fundamental constituents of matter (electrons) exchange information with each other (the analog of "talking") when they are transferred from one atom to another as the two atoms move by each other quickly. In the process to be studied, the two electrons come from a target atom and are captured by a fast moving projectile ion (an atom missing some electrons on it initially) accompanied by the emission of a single x ray. The process can be thought of as the inverse of the double ionization (removal of two electrons) by a single photon. This two-electron process is similar to the one-electron process in which an electron is liberated by a single photon. The latter process is known as the photoelectric effect, which was explained by Einstein in 1905, for which he was awarded the Nobel Prize, and which underlies much of modern technology. During the two-electron process the electrons "talk" with each other and coordinate the double photo-ionization. The same must occur in the time-reversed case when two electrons are transferred to a projectile, giving up a photon. There is considerable interest in studying this "talking" process, from the point of view of collisions between ions and target atoms and from the time-reversed process of double photo-ionization of an atom by a single photon. Theorists have calculated probabilities for the two-electron process, with results differing by factors of 1,000 or even 10,000. This wide range leaves the field open for experiments that will determine the actual probability accurately. Up to now, five experiments of two-electron transfer with simultaneous emission of a photon have been attempted at laboratories in the U.S. and Germany. One of these experiments (in the U.S.) was partially successful, but the others were not, mostly due to the long measuring times required to see the events. Notably, photon collision researchers would be very much interested in measuring double photo-ionization of two-electron ions, something they cannot yet do, except for the two-electron atom helium. The involvement of Ph.D. students in the planned research gives them valuable training in state-of-the-art physics experiments, and along with the preparation of collaborative manuscripts and abstracts, help make them productive young scientists.Technical description:The transfer of two electrons to an ion accompanied by the emission of a single photon is called radiative-double-electron capture, or RDEC for short. The intellectual merit of RDEC lies in its intrinsic fundamental interest in the field of ion collisions with quasi-free electrons, and its close relationship to photon interactions with highly-charged ions. This relationship is essentially the time inverse of RDEC, which is the process of double photo-ionization of ions. These inverse processes are particularly connected when RDEC occurs for incident fully-stripped ions and double photo-ionization for two-electron systems. RDEC has been investigated sparsely, and new studies will address complications of the previous data involving ion-solid interactions for oxygen and fluorine ions incident on a C foil, and will build upon these results by investigating RDEC for collisions with gas targets of He, N2 and Ne. An advantage of gas targets is that they do not introduce the effects of multiple collisions present for solid targets and the results are expected to clarify the questions that arose in the earlier work. RDEC can be compared with several theoretical calculations that differ by several orders of magnitude. By obtaining results for C-foil targets and for gas targets, both to be studied under this project, and by comparing the measurements with theory, it should be possible to obtain the first data that provides input to the theoretical calculations. The measurements will be done for fully-stripped fluorine ions using the tandem Van de Graaff at Western Michigan University. The particular apparatus for the proposed experiment, including the apparatus for the gaseous targets, is already in place (funded previously by the US DOE). Measurements will involve recording coincidences between x rays emitted and singly- and doubly-charged projectiles (the latter coincidences represent a signature for RDEC). The measurements are difficult due to the relatively small cross sections for RDEC (on the order of ~1 barn or less) and will require long counting times of more than a month.

非技术描述：该项目涉及对物质（电子）最小，最基本的组成部分（电子）如何彼此交换信息（“说话”的类似物）如何在两个原子彼此转移到另一个原子时如何相互交流。在要研究的过程中，这两个电子来自靶原子，并由快速移动的弹丸离子（最初缺少某些电子）捕获，并伴有单个X射线的发射。可以将该过程视为通过单个光子的双电离（去除两个电子）的倒数。这个两电子过程类似于单电子过程，其中电子被单个光子释放。后一个过程被称为光电效应，爱因斯坦于1905年解释，为此，他获得了诺贝尔奖，这是现代技术的基础。在两电子过程中，电子彼此“交谈”并协调双光电发。当两个电子被转移到弹丸，放弃光子时，必须在时间转换的情况下发生同样的情况。从离子和靶原子之间的碰撞的角度以及从单个光子对原子的双重光电期化的时间转换过程中，研究这个“说话”过程引起了很大的兴趣。理论家已经计算了两电子过程的概率，结果的因素为1,000甚至10,000。这个宽范围为实验打开了场，该实验将准确确定实际概率。到目前为止，已经尝试在美国和德国实验室同时发射两电子转移的五个实验。这些实验之一（在美国）取得了部分成功，但其他实验并非如此，这主要是由于观察事件所需的长时间测量时间。值得注意的是，光子碰撞研究人员将对测量两电子离子的双重光学化非常感兴趣，除了两电子原子氦气外，他们还不能做的事情。博士学位的参与计划研究的学生为他们提供了最先进的物理实验的宝贵培训，以及准备协作手稿和摘要的准备，有助于使它们富有生产力的年轻科学家。技术描述：将两个电子转移到伴随单个光子的离子伴随的离子中，称为辐射 - 双电子捕获，以供短暂捕获。 RDEC的智力优点在于其在与准电子的离子碰撞领域的内在基本兴趣，以及与光子与高电荷离子的密切关系。这种关系本质上是RDEC的倒数时间，RDEC是离子双光电离的过程。当发生完全分裂的离子和双电子系统的双重光电素时，这些反向过程尤其连接。对RDEC的研究很少，新的研究将解决先前数据的并发症，这些数据涉及氧气和氟离子的离子 - 固体相互作用，并通过调查与HE，N2和NE的气体碰撞的RDEC来建立这些结果。气体目标的一个优点是，它们没有引入对固体目标的多个碰撞的影响，并且结果有望阐明早期工作中出现的问题。可以将RDEC与几个理论计算进行比较，这些计算通过几个数量级不同。通过获得C线目标和气体目标的结果，既可以在此项目下进行研究，又可以将测量值与理论进行比较，应该可以获得为理论计算提供输入的第一个数据。这些测量将用于使用西密歇根大学的串联范德格拉夫（Van de Graaff）对完全拆下的氟离子进行测量。拟议的实验的特定设备，包括气体目标的设备，已经到位（以前由美国DOE资助）。测量结果将涉及记录发射和单次充电弹丸之间的X射线之间的一致性（后者的巧合代表了RDEC的签名）。由于RDEC的横截面相对较小（以〜1个谷仓的范围或更少），因此很难进行测量，并且需要长时间的时间超过一个月。