Precision Measurements with the CHIP-TRAP Mass Spectrometer for Tests of Special Relativity

该项目的目标是对氯-35和氯-36这两种氯原子之间的质量差进行非常精确的测量。这两种同位素有相同数量的质子和电子，所以它们有相同的化学性质，但是氯-36多了一个中子，所以它们的质量不同。然而，质量差不仅仅是中子的质量差。这是因为，根据爱因斯坦著名的方程E = mc2，多余中子的一些质量作为核结合能被放弃了。因此，通过测量氯-35和氯-36之间的质量差，并考虑中子的质量，可以确定氯-36的中子结合能。质量差测量结果给出了爱因斯坦方程的右侧，并且可以与其他独立的中子结合能测量结果进行比较，后者给出了爱因斯坦方程的左侧。其他的测量方法使用精确的光谱学技术来测量伽马射线（类似于x射线的高能电磁辐射）的能量，这种射线是在氯-35原子核捕获一个中子变成氯-36并释放多余能量后发出的。质量差和伽马射线能量的比较提供了E = mc2的直接检验。本项目将使用高精度彭宁阱质谱法，通过测量含有氯-35和氯-36同位素的单电荷离子在中密歇根大学高精度彭宁阱（CHIP-TRAP）的12特斯拉磁场中的回旋频率比，来确定氯-35和氯-36之间的质量差。回旋频率将使用图像电荷检测技术来确定，在该技术中，由振荡离子在陷阱电极中诱导的图像电流被检测并通过低噪声低温电路放大。CHIP-TRAP将由一种新颖的双测量陷阱结构组成，该结构将使两个离子的质量比被确定同时存储很长时间的测量时间。最终，两个离子的回旋加速器频率测量将同时进行，大大减少了时间磁场波动的影响。这种技术应能使质量比的精度达到万亿分之十或更小。离子将在Penning阱外使用激光烧蚀离子源或等离子体离子源产生，并在转移到精密测量阱之前被输送到捕获阱。这将减少实验所需的长寿命（30万年半衰期）氯同位素的数量。

The goal of this project is to perform a very precise measurement of mass difference between two types of chlorine atoms: Chlorine-35 and Chlorine-36. These two isotopes have the same number of protons and electrons, so they have the same chemical properties, but chlorine-36 has one extra neutron, so they do not have the same mass. However, the mass difference is not simply the mass of the neutron. This is because, according to Einstein's famous equation, E = mc2, some of the mass of the extra neutron is given up as nuclear binding energy. Hence, by measuring the mass difference between chlorine-35 and chlorine-36, and accounting for the mass of the neutron, the chlorine-36 neutron binding energy can be determined. The mass difference measurement gives the right hand side of Einstein's equation and can be compared with other, independent measurements of the neutron binding energy that give the left hand side of Einstein's equation. These other measurements use precise spectroscopy techniques to measure the energy of gamma-rays (high energy electromagnetic radiation similar to x-rays) that are emitted just after a chlorine-35 nucleus captures a neutron to become chlorine-36 and releases the excess energy. The comparison of the mass difference and gamma ray energies then provides a direct test of E = mc2. This project will use high-precision Penning trap mass spectrometry to determine the mass difference between chlorine-35 and chlorine-36 by measuring the ratio of cyclotron frequencies of singly-charged ions containing these isotopes in the 12 Tesla magnetic field of the Central Michigan University High Precision Penning Trap (CHIP-TRAP). The cyclotron frequency will be determined using the image charge detection technique in which the image currents induced in the trap electrodes by the oscillating ion are detected and amplified with low noise cryogenic circuits. CHIP-TRAP will consist of a novel, double measurement trap structure that will enable the two ions whose mass ratio is to be determined to be simultaneously stored for long measurement times. Ultimately, the cyclotron frequency measurement for the two ions will be performed simultaneously, greatly reducing the effect of temporal magnetic field fluctuations. This technique should enable a precision in the mass ratio of 10 parts per trillion or less to be reached. Ions will be produced outside of the Penning trap using either a laser ablation ion source or a plasma ion source, and will be transported to a capture trap before being transferred to the precision measurement traps. This will reduce the amount of the long-lived (300,000 year half-life) chlorine isotope required for the experiment.