本論文的目的是在清華水池式反應器（簡稱THOR）W3 實驗站建置去極化中子束(Neutron depolarization beamline)，用來進行磁性塊材內部磁特性之研究。實驗上，主要為觀察極化中子通過磁性材料後，其極化向量的變化來進行分析；從量測到的去極化因子(depolarization factor)及進動角度(precession angle)這兩個變數，可以觀察到材料內部平均磁區大小(mean domain size)、以及平均磁化感應強度(mean magnetic induction)。目前W3上的設備僅能進行一維中子極化之研究，未來將發展成為可進行三維研究的中子束線。

The purpose of this thesis is to construct a neutron depolarization (ND) beamline in the Tsing-Hua Open Pool Reactor (THOR) in order to measure the magnetic characteristics in the interior of magnetic materials. The ND experiments were carried out at W3 port of THOR (2 MW). The neutron beam with wavelength λ0 = 2.37 Å is chosen by graphite monochromator, and then polarized and analyzed by Heusler Cu2MnAl (111) crystals. The neutron polarization ratio of the beamline is about 82%. The depolarized neutrons were collected by a 3He detector. Four hundred neutron counts per second was achieved. A Ni75Fe25 sample was used to test the performance of this beamline. The measured depolarization factor is 0.789 and the procession angle is 2.61 rad, which imply the mean magnetic domain size is 34±7 μm and mean magnetic induction is 236.6 Oe has been investigated by ND technique in Ni75Fe25.

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