光泵抽运3He极化程度监控系统的设计与实现

闫松; 屠小青; 彭梅

doi:10.11938/cjmr20192720

波谱学杂志 >

2020 , Vol. 37 >Issue 1: 114 - 122

DOI: https://doi.org/10.11938/cjmr20192720

研究论文

光泵抽运³He极化程度监控系统的设计与实现

闫松 ,
屠小青 ,
彭梅

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1. 中国工程物理研究院核物理与化学研究所, 中子物理重点实验室, 四川绵阳 621900;
2. 北京交通大学理学院, 北京 100044

收稿日期: 2019-03-14

网络出版日期: 2019-05-30

基金资助

国家自然科学基金资助项目（11675152；91636103）.

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Design and Implementation of a Monitoring System for Measuring Polarization Degree of Optical Pumping ³He

YAN Song ,
TU Xiao-qing ,
PENG Mei

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1. Key Laboratory of Neutron Physics, Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900, China;
2. School of Science, Beijing Jiaotong University, Beijing 100044, China

Received date: 2019-03-14

Online published: 2019-05-30

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摘要

极化³He的一项重要应用是中子的极化.中国绵阳研究堆（CMRR）已建立国内首个自旋交换光学泵浦（SEOP）极化³He中子极化系统.为了监测³He的极化率随时间的相对变化情况，本文首先设计了基于核磁共振（NMR）技术的³He相对极化率测量系统，通过Matlab控制程序实现了对³He相对极化率的定时检测.然后对拾波线圈的构形和信噪比（SNR）进行了优化.结果表明当绕线长度一样时，Brooks构形的线圈有利于提高SNR；当线圈的平均半径为（a₀+d）/√2（a₀为³He气室的半径，d为拾波线圈与气室之间的距离）时，其SNR最高.最后对该系统的本底噪声进行了测量，发现其主要来源于环境噪声（0.27 μV/√Hz）和数据采集（DAQ）卡的噪声（0.40 μV/√Hz），系统的总噪声功率谱密度约为√0.16+0.073G² μV/√Hz（G为放大器的增益倍数）.

关键词： 自由感应衰减(FID); 核磁共振(NMR); 拾波线圈; 信噪比(SNR); 极化³He

本文引用格式

闫松 , 屠小青 , 彭梅 . 光泵抽运³He极化程度监控系统的设计与实现[J]. 波谱学杂志, 2020 , 37(1) : 114 -122 . DOI: 10.11938/cjmr20192720

Abstract

Spin polarized ³He is widely used to polarize neutrons as neutron spin filters (NSF). China Mianyang Research Reactor (CMRR) has established the first spin exchange optical pumping (SEOP) polarized ³He neutron polarization system in China. In order to monitor the relative change in the polarizability of ³He as a function of time, a ³He polarimetry system based on nuclear magnetic resonance (NMR) was designed and implemented, with which the ³He polarizability could be monitored regularly using Matlab programs. The configuration and signal-to-noise ratio (SNR) of the pickup coil were optimized. It was shown that, for a given length of winding wire, the design of a Brooks coil could improve the SNR, and achieve maximal SNR when the average radius of the coil set to (a₀+d)/√2, where a₀ is the radius of ³He cell, and d is the distance between the pickup coil and the cell. The noise floor level of the system was also measured, and shown to be dominated by environment noise (0.27 μV/√Hz) and data acquisition (DAQ) card noise (0.40 μV/√Hz). The power spectral density of the system was found to be approximately √0.16+0.073G² μV/√Hz, where G is the gain of the amplifier.

Key words： free induction decay (FID); nuclear magnetic resonance (NMR); pickup coil; signal to noise ratio (SNR); polarized ³He

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