Collaborative Research: Neutron Interferometry Experiments in Nuclear Physics

中子干涉仪通过单晶硅中的布拉格衍射将自由中子的波函数分成两束相干光束。由不同的路径长度、电势或束中的材料引起的相对相移在一个或多个中子计数器中产生干涉条纹。这个相位可以在干涉图中的几度内测量，因此可以高精度地确定样品中的中子相互作用势。该计划的重点是使用中子干涉测量法进行精确的中子散射长度测量的重要性，核物理。中子干涉仪测量相移，因此它可以直接获得散射长度。这是一个富有成效的，往往更精确的替代核散射实验，测量横截面（散射长度的乘积）。例如，在横截面测量中，受入射中子通量的不确定性限制;在相移测量中，这并不重要。实验包括精确测量几体中子散射长度，这对于通过半唯象模型和有效场论提高我们对核子-核子势的理解是重要的;以及中子均方电荷半径的精确测量，这是理解中子内部结构和动力学的重要量。根据量子力学理论，所有的物质在缓慢运动时都变成波浪状。物质波表现出通常与光波相关的波动特性，如衍射和折射。中子干涉仪利用硅晶体中的中子物质波衍射将慢中子束分成两条不同的路径。通过将测试样品放入其中一个路径，并观察由此产生的波干涉，我们可以精确地测量中子束与样品的相互作用。这种测量被用来提高我们对中子和物质之间的物理力的理解，以及对物质本身的基本子结构的理解。

A neutron interferometer splits the wave function of a free neutron into two coherent beams by Bragg diffraction in a single silicon crystal. The relative phase shift caused by different path lengths, potentials, or materials in the beams produces interference fringes in one or more neutron counters. This phase can be measured within a fraction of a degree in an interferogram so the neutron interaction potential in the sample can be determined to high precision. This program is focused on using neutron interferometry to make precision neutron scattering length measurements of importance to nuclear physics. The neutron interferometer measures a phase shift so it has direct access to the scattering length. This is a fruitful and often more precise alternative to nuclear scattering experiments which measure a cross section (a product of scattering lengths). For example, in a cross section measurement one is limited by uncertainty of the incident neutron flux; in a phase shift measurement that is not important. Experiments include precision measurement of few body neutron scattering lengths, important for improving our understanding of the nucleon-nucleon potential through semi-phenomenological models and effective field theories; and a precision measurement of the neutron mean-squared charge radius, an important quantity for understanding the internal structure and dynamics of the neutron.According to the theory of quantum mechanics, all matter becomes wave-like when it moves very slowly. Matter waves exhibit wave properties such as diffraction and refraction that are normally associated with light waves. A neutron interferometer uses neutron matter-wave diffraction in a silicon crystal to split a slow neutron beam into two distinct paths. By placing a test sample into one of these paths, and observing the resulting wave interference, we can precisely measure the interaction of the neutron beam with the sample. Such measurements are used to improve our understanding of the physical forces between neutrons and matter, and of the fundamental sub-structure of matter itself.