Collaborative Research: Neutron Interferometry Experiments in Nuclear Physics

中子干涉仪通过在单个硅晶体中的布拉格衍射将自由中子的波函数分成两个相干光束。由光束中不同的路径长度、电位或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。在干涉图中，这个相位可以在几分之一度内测量，因此样品中的中子相互作用势可以高精度地确定。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，这对核物理学具有重要意义。中子干涉仪测量相移，因此它可以直接获得散射长度。与测量截面（散射长度的乘积）的核散射实验相比，这是一种富有成果且往往更精确的替代方法。例如，在截面测量中，受入射中子通量不确定度的限制；在相移测量中，这并不重要。实验包括精确测量少量体中子散射长度，这对于通过半现象学模型和有效场论提高我们对核子-核子势的理解很重要；精确测量中子电荷均方半径，这是了解中子内部结构和动力学的重要量。根据量子力学理论，所有物质在非常缓慢地运动时都会变成波状。物质波表现出波的性质，如衍射和折射，这通常与光波有关。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。通过将测试样品放置在其中一个路径中，并观察产生的波干涉，我们可以精确地测量中子束与样品的相互作用。这样的测量被用来提高我们对中子和物质之间的物理作用力，以及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.