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

非技术描述：这个项目涉及调查物质(电子)的两个最小和最基本的成分(电子)在两个原子快速移动时如何从一个原子转移到另一个原子时彼此交换信息(类似于“说话”)。在被研究的过程中，这两个电子来自一个靶原子，并被一个快速运动的抛射离子(原子最初失去了一些电子)俘获，并伴随着一条X射线的发射。这个过程可以被认为是单光子双电离(移除两个电子)的逆过程。这种双电子过程类似于单电子过程，在单电子过程中，一个电子被单光子解放。后一种过程被称为光电效应，这是爱因斯坦在1905年解释的，他因此而获得诺贝尔奖，这是许多现代技术的基础。在双电子过程中，电子相互“对话”，协调双光致电离。同样的情况也必须发生在时间倒转的情况下，当两个电子转移到一个弹丸上，放弃一个光子。人们对从离子与靶原子之间的碰撞以及原子被单光子双光子光致电离的时间反转过程的角度来研究这种“说话”过程有相当大的兴趣。理论家已经计算了两电子过程的几率，结果相差1000甚至10000倍。这一宽广的范围为准确确定实际概率的实验敞开了大门。到目前为止，美国和德国的实验室已经尝试了五个双电子转移和同时发射一个光子的实验。其中一项实验(在美国)部分是成功的，但其他的则不是，主要是因为观看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两电子离子的双光致电离非常感兴趣，除了两电子原子氦之外，他们还无法做到这一点。博士生参与计划中的研究为他们提供了在最先进的物理实验方面的宝贵培训，以及合作手稿和摘要的准备，帮助他们成为多产的年轻科学家。技术描述：伴随着单光子发射的两个电子到一个离子的转移被称为辐射双电子俘获，简称RDEC。RDEC的智能优点在于它在离子与准自由电子碰撞领域的内在基本兴趣，以及它与光子与高电荷态离子相互作用的密切关系。这种关系本质上是RDEC的时间逆，RDEC是离子的双光电离过程。当入射的完全剥离离子和双电子系统的双光电离发生RDEC时，这些逆过程尤其相关。RDEC的研究一直很少，新的研究将解决先前数据的复杂性，这些数据涉及入射到C箔上的氧和氟离子的离子-固体相互作用，并将在这些结果的基础上，通过研究RDEC与He、N2和Ne气体目标的碰撞。气体靶的一个优点是，它们不会引入固体靶存在的多次碰撞的影响，预计结果将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。通过获得本项目下要研究的C-箔靶和气体靶的结果，并通过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。西密歇根大学的串列范德格拉夫将对完全剥离的氟离子进行测量。用于拟议实验的特定设备，包括用于气态靶的设备，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射线与单电荷和双电荷射弹之间的重合(后一种重合代表RDEC的特征)。由于RDEC的截面相对较小(约为~1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。

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.