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：该项目涉及研究物质（电子）的两个最小和最基本的成分当它们作为两个原子从一个原子转移到另一个原子时如何相互交换信息（类似于“说话”）。原子彼此快速移动。在要研究的过程中，两个电子来自目标原子，并被快速移动的射弹离子（最初缺少一些电子的原子）捕获，同时发射单个 X 射线。该过程可以被认为是单个光子的双电离（去除两个电子）的逆过程。这种双电子过程类似于单电子过程，其中电子由单个光子释放。后一个过程被称为光电效应，爱因斯坦于 1905 年对此进行了解释，并因此获得了诺贝尔奖，它是许多现代技术的基础。在双电子过程中，电子彼此“交谈”并协调双光电离。在时间反转的情况下，当两个电子转移到射弹并释放出一个光子时，也会发生同样的情况。从离子与目标原子之间的碰撞以及单个光子对原子的双光电离的时间反转过程的角度来看，人们对研究这种“说话”的过程非常感兴趣。理论家计算了双电子过程的概率，结果相差 1,000 甚至 10,000 倍。这一广泛的范围为准确确定实际概率的实验留下了空间。到目前为止，美国和德国的实验室已经尝试了五次同时发射光子的双电子转移实验。其中一项实验（在美国）取得了部分成功，但其他实验则没有成功，主要是因为观察事件所需的测量时间很长。值得注意的是，光子碰撞研究人员对测量双电子离子的双光电离非常感兴趣，但除了双电子原子氦之外，他们还无法做到这一点。博士的参与。计划研究中的学生为他们提供了最先进的物理实验方面的宝贵培训，并随着合作手稿和摘要的准备，帮助他们成为富有成效的年轻科学家。技术描述：两个电子转移到一个离子伴随发射单个光子的过程称为辐射双电子捕获，简称 RDEC。 RDEC 的智力优势在于其对离子与准自由电子碰撞领域的内在根本兴趣，以及它与光子与高电荷离子相互作用的密切关系。这种关系本质上是 RDEC 的时间倒数，即离子的双光电离过程。当入射完全剥离离子发生 RDEC 和双电子系统双光电离时，这些逆过程尤其相关。 RDEC 的研究很少，新的研究将解决先前数据的复杂性，涉及 C 箔上发生的氧和氟离子的离子-固体相互作用，并将通过研究 RDEC 与 He、N2 气体目标的碰撞来建立在这些结果的基础上和氖。气体目标的一个优点是它们不会引入固体目标存在的多次碰撞的影响，并且结果有望澄清早期工作中出现的问题。 RDEC 可以与几个相差几个数量级的理论计算进行比较。通过获得本项目要研究的 C 箔目标和气体目标的结果，并将测量结果与理论进行比较，应该可以获得为理论计算提供输入的第一批数据。将使用西密歇根大学的串联范德格拉夫装置对完全剥离的氟离子进行测量。所提议的实验的特定设备，包括用于气体目标的设备，已经就位（之前由美国能源部资助）。测量将涉及记录发射的 X 射线与单电荷和双电荷射弹之间的重合（后者重合代表 RDEC 的特征）。由于 RDEC 的横截面相对较小（约为 1 个谷仓或更小），测量很困难，并且需要长达一个月以上的计数时间。