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被激发但没有立即衰变回基态时，就会出现核异构体。四十年前，在钍229中发现了一种核异构态，它具有特别不寻常的特性。 该态的能量仅比基态高8电子伏，半衰期为15分钟。 这是已知的最低能量核跃迁，可以使用真空紫外区 (VUV) 的激光来激发它。 如果可以利用这种转变，那么它将允许使用激光来操纵核状态，这是以前从未做过的。最终目标是利用这种状态的特征来研究现代科学中最引人注目的问题之一：自然常数实际上是常数吗？此外，异构态应该允许建造一种核时钟，其性能可能优于所有当前和计划中的光学时钟，从而改善导航和通信。 此前，Thorium-229 异构态是通过粒子加速器中的高能碰撞产生的。该奖项将使加州大学洛杉矶分校的研究团队能够使用台式激光器创建异构体，并精确测量激发能量，从而将我们对跃迁能量的了解提高 4 到 5 个数量级。研究小组将使用定制的 VUV 激光系统来激发掺杂钍 229 的晶体和含有 A = 229 同位素的氧化钍样品从基态到异构态的转变。就晶体而言，原子核的任何激发都会随后产生核荧光，该荧光将被灵敏的光子探测器检测到。就金属而言，原子核的任何激发都会随后导致内部转换电子的发射，该电子将被灵敏的电子探测器检测到。将监测这些信号以确定核态的跃迁能量和寿命。一旦找到过渡，将通过将初步的钍钟架构与更成熟的原子钟进行比较来探索过渡用作时钟振荡器的潜力。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准。