Precision Measurements on Ions

佛罗里达州立大学的精密潘宁阱质谱仪是世界上最精确的测量原子质量的系统之一（更通俗地说，是“称重原子”）。原子的质量是原子的基本性质，原子质量在物理和化学中有许多重要的应用。特别是，由于能量和质量的等效（通过“E = mc2”），原子质量的差异决定了核反应中释放的能量。虽然许多原子质量已经被精确地测量了，但是在一些重要的科学应用中，仍然需要更高精度的测量。这些应用包括确定更精确的“基本常数”值，以及确定中微子的质量，中微子是一种非常轻且相互作用弱的基本粒子，遍布宇宙。基本常数（例如，电子和质子的质量）基本上是物理学中所有计算都需要的。但特别需要的是更精确的数值，这样包含在粒子物理学所谓的“标准模型”中的理论才能与实验结果进行精确的比较。如果理论和实验结果之间的差异被发现，这可能会导致如何修改标准模型的见解，尽管标准模型在解释大多数观测方面取得了巨大成功，但它无法解释，例如，目前神秘的暗物质和暗能量现象。同时，该项目为从高中到博士后的学生研究人员提供许多广泛适用的科学技术方面的培训，为他们在工业和国家实验室以及学术界的职业生涯做好准备，从而为受过科学训练的劳动力做出贡献。基本方法是使用相相干技术在精密、低温、8.5特斯拉的Penning离子阱中测量单个离子的回旋频率比，并使用dc-SQUID通过图像电流检测离子。要完成的测量将包括氘核与质子的质量比（与氢、氘及其双原子分子的超精密光谱有关）、氚与氦-3的质量比（与中微子质量有关）、碱金属的原子质量（用于精细结构常数）、钙同位素链（用于测试量子电动力学理论）和其他同位素链（用于寻找所谓的King-plot线性同位素位移的偏差）。这可能指向新的物理学)。为了使某些测量的精度达到万亿分之一，PI计划开发一种方法，用于同时测量Penning陷阱中两个离子的回旋加速器频率，其中两个离子处于耦合磁控管轨道上。（这种方法最初是在2000年麻省理工学院开发的，但只应用于四个离子对，而不是氢或氦同位素。）通过同步测量回旋加速器频率，可以极大地抑制磁场变化的影响，而磁场变化是造成回旋加速器频率比测量统计不确定性的主要原因。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Florida State University precision Penning trap mass spectrometer is one of the world's most precise systems for measuring atomic masses (more colloquially, for "weighing atoms"). An atom's mass is a basic property and atomic masses have many important applications in physics and chemistry. In particular, because of the equivalence of energy and mass (through "E = mc2"), atomic mass differences determine the energy released in nuclear reactions. Although many atomic masses have already been precisely measured there are several scientifically important applications where measurements at still higher precision are required. These applications include determining more precise values of the "fundamental constants," and determining the mass of the neutrino, an extremely light and weakly interacting fundamental particle that pervades the universe. The fundamental constants (for example, the masses of the electron and proton) are needed for essentially all calculations in physics. But in particular, ever-more precise values are needed so that the theories included in the so-called "Standard-Model" of particle physics can be precisely compared with experimental results. If discrepancies between the results of theory and experiment are discovered, this may lead to insights into how to modify the Standard Model, which despite great success in explaining most observations, is unable, for example, to explain the currently mysterious phenomena of Dark Matter and Dark Energy. At the same time the project provides training for student researchers, from high-school to post-doctoral, in many widely applicable scientific techniques, preparing them for careers in industry and national laboratories as well as academe, hence contributing to the scientifically trained workforce.The basic method is to measure ratios of cyclotron frequencies of single ions in a precision, cryogenic, 8.5 tesla Penning ion trap using phase-coherent techniques, with ion detection via image currents using a dc-SQUID. Measurements to be accomplished will include the mass ratio of the deuteron to the proton (relevant to ultra-precise spectroscopy of hydrogen, deuterium and their diatomic molecules), of tritium to helium-3 (relevant to neutrino mass), the atomic masses of alkali metals (for the fine structure constant), of chains of calcium isotopes (for testing quantum-electrodynamics theory), and other isotope chains (for searches for deviations from so-called King-plot linearity of isotope shifts, which may point to new physics). Aiming for a few parts-per-trillion fractional precision for some measurements, the PI plans to develop a method for the simultaneous measurement of the cyclotron frequencies of two ions in a Penning trap, in which the two ions are in a coupled magnetron orbit. (This method was initially developed at MIT c. 2000, but was only applied to four ion pairs, and not to hydrogen or helium isotopes.) By measuring the cyclotron frequencies simultaneously, the measurement will greatly suppress the effect of variation in the magnetic field, which is the main cause of statistical uncertainty in the measurements of a cyclotron frequency ratio.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.