Laser Excitation of the 229-Th Nuclear Isomer

虽然典型的核激发能在keV到mev的范围内，但也有几种例外情况下的激发能要低得多。这个项目的主题是钍-229同位素，它在紫外光光谱中具有独特的激发态。在过去的十年中，对这个范围内的光发射进行了几次实验研究，但都没有成功或没有结果。除了在错误的能量区域进行搜索外，搜索还受到了核转换窄线宽的挑战。在这项工作中，将采用交替的电子-桥式跃迁来初始激光激发Th-229中的核异构体能级。由于原子核内部强相互作用和弱相互作用的相互作用，原子核的转变很可能对基本常数的变化特别敏感。在确定异构化能级后，将确定核跃迁对精细结构常数随时间变化的敏感性，这一研究将在多个物理和技术领域产生广泛的影响。激光激发和对核态的相干操纵将在原子物理和核物理之间建立一座新的桥梁，有望使频率测量达到新的精度水平。该项目将涉及广泛的研究生和本科生培训和参与。

While typical nuclear excitation energies are in the keV to MeV range, there are several exceptional cases where the excitation energies are much lower. The subject of this project is the thorium-229 isotope, which, uniquely, has an excited state in the UV optical spectrum. Several experimental searches for optical emission in this range undertaken in the past ten years were unsuccessful or inconclusive. In addition to searching in the wrong energy region, the searches were challenged by the narrow linewidth of the nuclear transition. In this work, an alternative electron-bridge transition will be employed for the initial laser excitation of the nuclear isomer level in thorium-229. The nuclear transition is likely to be exceptionally sensitive to the variation of fundamental constants, due to the interplay of the strong and electroweak interactions inside this nucleus. After the isomer level is found, the sensitivity of the nuclear transition to time variation of the fine structure constant will be determined.This research will have broad impact across several areas of physics and technology. Laser excitation and coherent manipulation of nuclear states would establish a new bridge between atomic and nuclear physics, with the promise of new levels of accuracy for frequency metrology. The project will involve extensive graduate and undergraduate student training and participation.