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

非技术描述：该项目涉及研究物质的两个最小和最基本的成分（电子）如何在两个原子快速相互移动时从一个原子转移到另一个原子时相互交换信息（类似于“说话”）。在待研究的过程中，这两个电子来自一个目标原子，并被一个快速移动的抛射离子（一个原子最初缺少一些电子）捕获，同时发射出一条x射线。这个过程可以被认为是单光子双电离（去除两个电子）的逆过程。这个双电子过程类似于一个电子被一个光子释放的单电子过程。后一种过程被称为光电效应，爱因斯坦在1905年解释了这一现象，并因此获得了诺贝尔奖，它是现代技术的基础。在双电子过程中，电子相互“交谈”并协调双光离。在时间反转的情况下，当两个电子转移到抛射体上，放弃一个光子时，也会发生同样的情况。从离子与靶原子碰撞的角度和从单光子使原子双光离的逆时过程的角度来看，人们对研究这种“谈话”过程有相当大的兴趣。理论学家已经计算出双电子过程的概率，结果相差1000甚至10000倍。如此大的范围为精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进行了5次双电子转移同时发射光子的实验。其中一个实验（在美国）取得了部分成功，但其他的都没有成功，主要是因为观察这些事件所需的测量时间很长。值得注意的是，光子碰撞研究人员将对测量双电子离子的双光电离非常感兴趣，除了双电子原子氦之外，他们还无法做到这一点。博士生参与计划中的研究，使他们在最先进的物理实验方面得到了宝贵的训练，并准备了合作手稿和摘要，帮助他们成为富有成效的年轻科学家。技术描述：将两个电子转移到一个离子上，同时发射一个光子，这被称为辐射双电子捕获，简称RDEC。RDEC的智力价值在于它对准自由电子离子碰撞领域的内在基本兴趣，以及它与高电荷离子的光子相互作用的密切关系。这种关系本质上是RDEC的时间逆，RDEC是离子的双光离过程。当入射完全剥离离子发生RDEC和双电子系统发生双光电离时，这些逆过程特别相关。RDEC的研究很少，新的研究将解决先前数据的复杂性，包括氧和氟离子在C箔上的离子-固体相互作用，并将通过研究RDEC与He， N2和Ne气体目标的碰撞来建立这些结果。气体目标的一个优点是，它们不引入固体目标的多重碰撞效应，结果有望澄清早期工作中出现的问题。RDEC可以与几个不同数量级的理论计算相比较。通过获得本项目研究的c箔靶和气体靶的结果，并将测量结果与理论进行比较，应该有可能获得为理论计算提供输入的第一批数据。测量将使用西密歇根大学的串联范德格拉夫对完全剥离的氟离子进行。拟议实验的特定设备，包括气体目标设备，已经到位（之前由美国能源部资助）。测量将包括记录发射的x射线与单荷和双荷射弹之间的一致性（后者的一致性代表RDEC的特征）。由于RDEC的横截面相对较小（约1谷仓或更少），测量很困难，并且需要一个多月的长时间计数。

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.