Development of a Polarizer/Adiabatic Spin-Flipper for Ultra-Cold Neutrons

这笔赠款支持开发一种仪器，用于极化超冷中子(UCN)，并通过绝热快速通道(AFP)程序控制UCN极化的方向。该装置产生的极化强度与量子化轴平行或反平行，应为0.999%或更大，比目前可用的中子极化方案大约提高一个数量级。这台仪器的建造构成了普林斯顿大学在探索中子和中子β衰变基本性质的一系列实验发展中的主要贡献。这一系列中的第一项测量是确定极化中子衰变后发射电子的角分布。平行于中子自旋的发射率和反平行于中子自旋的发射率之差，即“β不对称”，可以用来求出核子的半轻子弱相互作用的轴向形状因子值，也可以用来确定Cabibbo-Kobayashi-Maskawa矩阵的元素之一。这项实验的成功关键取决于是否有一种仪器可以极化和翻转UCN自旋。

This grant supports the development of an instrument to polarize ultra-cold neutrons (UCNs) and to control the direction of UCN polarization through an adiabatic fast passage (AFP) procedure. The magnitude of the polarization produced, either parallel or antiparallel to the quantization axis, by this apparatus should be 0.999 percent or greater, representing roughly an order of magnitude improvement over neutron polarization schemes available at present. Construction of this instrument constitutes the primary Princeton contribution in the development of a series of experiments probing the fundamental properties of the neutron and neutron beta-decay. The first measurement in this series is a determination of the angular distribution of emitted electrons following the decay of polarized neutrons. The difference between the emission rate parallel to the neutron spin and the rate anti-parallel to the neutron spin, the "beta-asymmetry," can be used to find the value of the axial form-factor for semi-leptonic weal interactions of the nucleon and also to determine one of the elements of the Cabibbo-Kobayashi-Maskawa matrix. The success of this experiment depends critically on the availability of an instrument to polarize and flip UCN spins.