Spectroscopy of the 7s-8s highly forbidden transition in laser-trapped francium

自然力是可以在加拿大国家核物理和粒子物理实验室TRIUMF的ISAC辐射束设施中研究的迷人课题之一。特别是，导致原子核β衰变的弱力，在呈现宇称破坏现象方面是独一无二的：在自然界中，没有观察到由弱力中介的物理过程的镜像。ISAC提供了研究Fr中原子宇称破坏的可能性，Fr是一种将非常重的核(Z=87)与简单的、基本上类似氢的碱的价态结构结合在一起的元素。在元素周期表的前103种元素中，FR核是最不稳定的，寿命最长的同位素只在23分钟内衰变。为了最大限度地利用微小样品，用激光减慢Fr原子的速度，并将其捕获到一个“磁光”激光陷阱中，该陷阱悬浮在自由空间中，温度比室温低数百万倍。我们已经在国际SAC建立了一个采集乳剂的设施；与来自美国、墨西哥和中国的研究人员合作，我们现在正在使用这个乳剂源，利用激光和微波光谱学进行一系列精密实验。在其中一项实验中，我们将使用本申请中所要求的激光设备来激发金中极微弱的电子跃迁，并详细研究其性质。这种跃迁的强度对法郎原子中的相对论效应非常敏感，它的测量允许与最先进的原子理论进行比较。此外，Fr中的7S-8S跃迁是未来可能的原子宇称破坏实验的基础。

The fundamental forces of nature are one of the fascinating subjects that can be studied at the ISAC radioactive beam facility at TRIUMF, Canada's national laboratory for nuclear and particle physics. In particular, the weak force, causing the beta-decay of nuclei, is unique in exhibiting the phenomenon of parity-violation: the mirror images of physical processes mediated by the weak force are not observed in nature. ISAC offers the possibility to study atomic parity-violation in francium (Fr), an element combining a very heavy nucleus (Z=87) with the simple, essentially hydrogenlike, valence structure of an alkali. Fr nuclei are the least stable among the first 103 elements in the periodic table, the longest-lived isotope decays in only 23 minutes. To make optimum use of the minute sample, the Fr atoms are slowed down with laser light and captured into a `magneto-optical' laser trap, suspended in free space at temperatures millions of times colder than room temperature. We have established a francium trapping facility at ISAC; in collaboration with researchers from the United States, Mexico, and China, we are now using this francium source to carry out a series of precision experiments using laser and microwave spectroscopy. In one of them, we will use the laser equipment requested in this application to excite an exceedingly faint electronic transition in francium, and study its properties in detail. The strength of this transition is very sensitive to relativistic effects in the francium atom and its measurement allows a comparison to state-of-the-art atomic theory. In addition, the 7s-8s transition in Fr is the basis for a possible, future atomic parity-violation experiment.