Investigation of the Low-Lying Nuclear Isomeric Transition in the A=229 Isotope of Thorium

钍A=229同位素低位核异构转变的研究

• 批准号: 2013011
• 负责人: Eric Hudson
• 金额: $ 56.07万
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2013011&HistoricalAwards=false
• 关键词: Investigation; Low; Lying; Nuclear; Isomeric

A nuclear isomer occurs when protons or neutrons in an atomic nucleus become excited but do not immediately decay back to their ground state. Forty years ago, a nuclear isomeric state was discovered in Thorium-229 which has especially unusual characteristics. The energy of this state is only 8 electron volts above the ground state and it has a half-life of 15 minutes. This is the lowest energy nuclear transition known and it can potentially be excited using lasers in the vacuum ultraviolet region (VUV). If the transition can be harnessed, then it would allow for the manipulation of a nuclear state using lasers, which has never been done before. The ultimate goal is to use the characteristics of this state to investigate one of the most compelling questions in modern science: Are the constants of nature actually constants? Further, the isomeric state should allow the construction of a nuclear clock which may outperform all current and planned optical clocks, thereby improving navigation and communication. Previously, the Thorium-229 isomeric state has been produced using high energy collisions in a particle accelerator. This award will enable a research team from UCLA to create the isomer using table-top lasers, and to precisely measure the excitation energy, improving our knowledge of the transition energy by 4 to 5 orders of magnitude. The research team will use a custom VUV laser system to excite the transition from the ground state to the isomeric state in both a crystal doped with thorium-229 and a sample of thorium oxide containing the A = 229 isotope. In the case of the crystal, any excitation of the nucleus will subsequently lead to nuclear fluorescence which will be detected by sensitive photon detectors. In the case of the metal, any excitation of the nucleus will subsequently lead to emission of an internal conversion electron which will be detected by a sensitive electron detector. These signals will be monitored to determine the transition energy and lifetime of the nuclear state. Once the transition is found, the potential of the transition for use as a clock oscillator will be explored by comparing a preliminary thorium clock architecture to more established atomic clocks.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

当原子核中的质子或中子变得兴奋，但不会立即衰减其基态时，就会发生核异构体。四十年前，在Thorium-229中发现了一个核异构体状态，其特征尤为异常。 该状态的能量仅高于基态的8个电子伏，半衰期为15分钟。 这是已知的最低能量核转变，并且可以使用真空紫外线区域（VUV）中的激光来激发它。 如果可以利用过渡，那么它将允许使用以前从未做过的激光器来操纵核国。最终目标是利用该州的特征来研究现代科学中最引人注目的问题之一：自然的常数实际上是常数吗？此外，异构体应允许建造一个核时钟，该核时钟可能胜过所有当前和计划的光学时钟，从而改善导航和通信。 以前，Thorium-229异构体是使用粒子加速器中的高能量碰撞产生的。该奖项将使UCLA的研究团队能够使用台式激光器创建异构体，并精确地衡量激发能量，从而将我们对过渡能量的知识提高4到5个数量级。研究团队将使用自定义的VUV激光系统在掺有thorium-229的晶体和含有A = 229同位素的氧化甲状腺样本的晶体中激发从基态到异构体状态的过渡。在晶体的情况下，核的任何激发将随后导致核荧光，这将由敏感的光子检测器检测。在金属的情况下，核的任何激发随后都会导致内部转化电子的发射，该电子将被敏感的电子检测器检测。这些信号将受到监控，以确定核国家的过渡能量和寿命。一旦找到过渡，将通过将初步的thor thor时钟体系结构与更既定的原子时钟进行比较，将探索用作时钟振荡器的过渡的潜力。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子和更广泛影响的审查审查标准来通过评估来通过评估来获得支持的。