Laser Excitation of the 229-Th Nuclear Isomer

虽然典型的核激发能在keV至MeV范围内，但也有几种例外情况，其中激发能要低得多。该项目的主题是钍-229同位素，它在紫外光谱中具有独特的激发态。在过去的十年里，在这个范围内进行了几次光学发射的实验研究，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之外，搜索还受到核跃迁的窄线宽的挑战。在这项工作中，另一种电子桥跃迁将用于钍-229核异构能级的初始激光激发。由于该核内强相互作用和电弱相互作用的相互作用，核跃迁可能对基本常数的变化特别敏感。在发现同质异能态后，将确定核跃迁对精细结构常数随时间变化的敏感性，这项研究将在物理和技术的多个领域产生广泛的影响。激光激发和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，并有望使频率计量达到新的准确度水平。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.