Precision Measurements on Ions

非技术描述：佛罗里达州立大学低温潘宁阱质谱仪是目前世界上最精确的测量原子质量的仪器（更通俗地说，为“原子称重”）。原子的质量是一种基本性质，因此原子质量在化学和物理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。虽然许多原子的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。这些应用包括确定中微子的质量，中微子是一种极轻且相互作用弱的基本粒子，遍布宇宙。多年来，人们一直认为中微子没有质量。我们现在知道情况并非如此，这一新知识提出了有关宇宙起源和结构的基本问题。该项目还为可能在学术界、工业界或国家实验室从事职业的学生和博士后研究人员提供培训，从而为受过科学训练的劳动力做出贡献。技术描述：我们提出的三个测量将提供原子质量差异，或核q值，这将用于其他项目的系统测试，这些项目寻求设定低能β衰变中电子反中微子质量的上限。这些是3T-3He质量差的测量结果是正在进行的，超大规模的氚衰变光谱仪KATRIN；以及187Re-187Os和163Ho-163Dy的质量差，这些项目将使用微热量计-衰变光谱仪。对光离子的其他测量将减少质子原子质量的不确定性。另一个质量差，35Cl-36Cl，将使精确的伽马射线计量检查成为可能。对40,48ca的原子质量的测量也在计划之中，以便对40,48ca19 +进行精确的g因子测量，以测试类氢离子的g因子的相对论原子理论，并探索对核结构的依赖。测量将包括在FSU Penning陷阱质谱仪的8.5特斯拉磁场中离子对回旋加速器频率的比值。这种光谱仪的独特之处在于，它能够在潘宁阱中制造和分离几乎任何元素的单个离子；利用耦合到dc-SQUID的高q超导调谐电路，通过图像电流对离子的轴向运动进行相参检测；通过在回旋加速器与轴向耦合频率下使用rf - pi脉冲将回旋加速器相位映射到轴向运动来测量离子的回旋加速器频率。由于磁场变化引起的回旋加速器频率噪声通过同时捕获两个离子来降低。

Non-technical description:The Florida State University cryogenic Penning trap mass spectrometer is currently the world's most precise apparatus for measuring atomic masses (more colloquially, for "weighing atoms"). The mass of an atom is a basic property and so atomic masses have many important applications in chemistry and physics. 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 the mass of the neutrino, an extremely light and weakly interacting fundamental particle that pervades the universe. For years it was believed that the neutrino had no mass. We now know this not to be the case, and this new knowledge raises fundamental questions concerning the origin and structure of the universe. The project also provides training for student and post-doctoral researchers who are likely to make careers in academe, industry or national laboratories, hence contributing to the scientifically trained workforce.Technical description:Three of the measurements we propose will provide atomic mass differences, or nuclear Q-values, that will be used to test systematics in other projects that seek to set upper limits on the mass of the electron anti-neutrino from low energy beta-decays. These are measurements of the 3T-3He mass difference for the ongoing, very-large-scale tritium beta-decay spectrometer KATRIN; and the mass differences 187Re-187Os and 163Ho-163Dy, for projects that will use micro-calorimeter beta-decay spectrometers. Other measurements on light ions will reduce the uncertainty of the atomic mass of the proton. Another mass difference, 35Cl-36Cl, will enable a check of precision gamma-ray metrology. Measurements of the atomic masses of 40,48Ca are also planned, to enable ongoing precision g-factor measurements of 40,48Ca19+ to test relativistic atomic theory for the g-factor of hydrogen-like ions and to probe the dependence on nuclear structure. The measurements will consist of ratios of cyclotron frequencies of pairs of ions in the 8.5 tesla magnetic field of the FSU Penning trap mass spectrometer. Unique features of this spectrometer include the ability to make and isolate, in the Penning trap, a single ion of nearly any element; phase-coherent detection of the axial motion of an ion, via image currents, using a high-Q super-conducting tuned-circuit coupled to a dc-SQUID; and measurement of the ion's cyclotron frequency by mapping evolved cyclotron phase onto axial motion using an rf pi-pulse at the cyclotron-to-axial coupling frequency. Cyclotron frequency noise due to variation in the magnetic field is reduced by trapping both ions in the pair simultaneously.