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

我们利用脉冲极化白色中子束开发了一种新型的极化中子光谱法。本方法的原理如下。通过使用自旋脚钳线圈调制脉冲入射中子束的极化，该旋转钳线圈的驱动电流是根据伪随机二进制序列（PRB）调节的。偏振调制受到控制，以使PRB模式在由中子爆发触发的每个顺序计数框架上周期性移动。该过程一直持续到PRB的一个周期移位，然后重复一个散射中子计数的新序列。这样，散射的中子事件被计数以二维时间分析仪计数，其中一个时间标签是总TOF，另一个对应于代表PRBS的移位数的计数帧数。使用适当的PRB模式在每个总TOF通道处沿着帧数轴的交叉相关...更多恢复了二维TOF频谱，其特征在于样品和总TOF。由于仅调制入射中性的极化，因此恢复的TOF光谱由一个频谱组成，该光谱与自旋脚钳和-OFF光谱之间的差异成正比，以及其他平坦的背景。中性的自旋脚钳系统和二维时间分析仪为本工作构建。控制脚钳线圈的驱动电流强度与1/t关系成正比，每个中子爆发的时间是在其中，以确保任何入射中子能量的中子自旋的180度翻转。然后根据PRB打开和关闭电流。开关的时机由一个模块给出，该模块生成PRBS模式，该模式在中子突发的每个帧中移动一步。根据其总飞行时间和帧数，在二维时间分析仪的适当记忆中计数散射的中子事件。旋转波散射的测量是在Kek的Spallation Neutron Source Kens的笔谱仪上进行的。该样品是铁磁啤酒合金Cu2mnal的单个晶体。我们可以在单个测量中观察到（Q，Omega）范围的旋转波散射。本实验的结果表明，在各种磁性材料中，脉冲极化白色中子束与偏振法的互相关方法的组合非常有望研究磁兴奋或波动。为了获得良好分辨率的结果，当然需要强烈的脉冲中子源。较少的