Development of a New Pulsed Polarized Neutron Spectroscopy Using Crosscorrelation Method

使用互相关方法开发新型脉冲偏振中子能谱

基本信息

批准号：
63840007
负责人：
KOHGI Masahumi
金额：
$ 7.04万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Developmental Scientific Research (B).
财政年份：
1988
资助国家：
日本
起止时间：
1988 至 1990
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-63840007/
关键词：
Pulsed Neutron Beam Polarized Neutrons Crosscorrelation Method Neutron Scattering Spin Waves 中性子分光

项目摘要

We developed a new type of polarized neutron spectroscopy utilizing a pulsed polarized white neutron beam. The principle of the present method is as follows ; The polarization of the pulsed incident neutron beam is modulated by using a spin flipper coil whose driving current is modulated according to a pseudorandom binary sequence (PRBS). The polarization modulation is controlled so that the PRBS pattern shifts cyclically at each sequential counting frame triggered by the neutron burst. The procedure continues until one cycle shift of the PRBS is finished, and then it repeats a new sequence of the counting of scattered neutrons. In this way, the scattered neutron events are counted in a two-dimensional time analyzer, one time label of which is the total TOF, and the other corresponding to the counting frame number which represents the shift number of the PRBS. The crosscorrelation of theacount rate along the frame number axis at each total TOF channel with the appropriate PRBS pattern … More recovers the two dimensional TOF spectrum which is characterized by the incident time at the sample and the total TOF. Since only the polarization of the incident neutrons is modulated, the recovered TOF spectrum consists of a spectrum which is proportional to the difference between the spin flipper-on and -off spectra and an otherwise flat background.A neutron spin flipper system and a two dimensional time analyzer were constructed for the present work. The driving current intensity for the flipper coil is controlled to be proportional to the 1/t relation, where is the time from each neutron burst, so that a 180 degree flip of the neutron spin is ensured for any incident neutron energy. The current is then switched on and off according to the PRBS. The timing of the switching is given by a module which generates the PRBS pattern which shifts by one step at each frame of the neutron burst. The scattered neutron events are counted in the appropriate memories in the two dimensional time analyzer according to their total flight time and frame number.The measurement of spin wave scattering were carried out on the PEN spectrometer at the spallation neutron source KENS at KEK. The sample was a single crystal of ferromagnetic Heusler alloy Cu2MnAl. We could observed spin wave scattering in a wide range of (Q, omega) space in a single measurement. The results of the present experiment show that the combination of the pulsed polarized white neutron beam with the crosscorrelation method with polarization modulation is quite promising for the study of magnetic excitations or fluctuations in various magnetic materials. In order to obtain results with good resolution an intense pulsed neutron source is required of course. Less

我们开发了一种利用脉冲偏振白中子束的新型偏振中子谱，该方法的原理如下：通过使用自旋翻转线圈来调制脉冲入射中子束，其驱动电流根据以下公式进行调制。控制伪随机二进制序列 (PRBS)，以便 PRBS 模式在中子爆发触发的每个连续计数帧处循环移位。 PRBS完成，然后重复新的散射中子计数序列，这样，在二维时间分析器中对散射中子事件进行计数，其中一个时间标签是总TOF，另一个时间标签对应。到表示 PRBS 移位数的计数帧数每个总 TOF 通道上的计数率与适当的 PRBS 模式的互相关可恢复以事件为特征的二维 TOF 频谱。由于仅调制了入射中子的极化，因此恢复的 TOF 光谱由与自旋翻转器开启和关闭光谱与其他平坦背景之间的差异成比例的光谱组成。目前的工作构建了中子自旋翻转系统和二维时间分析仪，翻转线圈的驱动电流强度被控制为与 1/t 关系成正比，其中是每个中子爆发的时间，因此对于任何入射中子能量，确保中子自旋发生 180 度翻转。然后根据 PRBS 切换电流。切换的时间由生成 PRBS 模式的模块给出，该模式每次移动一步。中子爆发的帧中的散射中子事件根据它们的总飞行时间和帧数在二维时间分析器中的适当存储器中进行计数。自旋波散射的测量在PEN能谱仪上进行。 KEK 的散裂中子源 KENS 的样品是铁磁 Heusler 合金 Cu2MnAl 的单晶，我们可以在一次测量中观察到大范围的（Q，omega）空间中的自旋波散射。脉冲偏振白中子束与偏振调制互相关方法的结合对于研究各种磁性材料的磁激发或涨落非常有前景。获得良好分辨率的结果当然需要更少的强脉冲中子源。