Development of Thermal Neutron Spin-Echo Spectroscopy

这一发展的目的是将常规热中子三轴能谱仪的能量分辨率提高到相对值10^&lt；-4&gt；利用中子自旋回波方法测量入射中子能量E_i或更好。为此目的，研制了具有“最佳场形”(OFS)的特殊Larmor进动磁体。根据变分场积分均匀问题的解析解，这种磁体是均匀线积分和低边缘场的最佳折衷，磁体的剩余线积分不均匀性和由于较大的束流发散引起的路径长度效应被束内螺旋线圈校正，在14.7 MeV的入射中子能量下，OFS线圈的最大场积分达到0.06Tm，对应于0.16纳秒的傅里叶时间，获得了-0.2mueV的近似分辨率，而相同TASConf…的分辨率为2.2meV不需要自旋回声。这种带有自旋回声(TASSE)选项的三轴光谱仪可以在一天半的时间内安装在传统的三轴仪器上。当动量传递改变到最大谱线值Q-3.6*^&lt；-1&gt时，自旋回波偏振完全保持不变；利用KDCO_3中有序-无序相变附近准弹性扩散散射的实验数据，证明了这种新的高分辨率TASSE方案的性能。首次获得了动态黄散射的证据，它可以看作是应变场介导的有序-无序相变的特征。此外，还研究了铬中的自旋密度波作为反铁磁自旋回波实验的例子。在SrTiO_3上进行了实验。用热中子自旋回波谱重新研究了中心分量的问题，并对钛酸锶在DELTAE-6 meV声子模下的有限能量转移自旋回波进行了初步研究。较少

The aim of this development is to improve the energy resolution of a conventional thermal neutron triple axis spectrometer to relative values of 10^<-4> of the incident neutron energy E_i or better by means of the Neutron Spin Echo method.For this purpose special Larmor precession magnets with "Optimal Field Shape" (OFS) have been developed and constructed.Following the analytical solution of the variational field-inteqral homogeneity problem, such magnets are the best compromise for homogeneous line integrals and low fringe-fields, The residual line integral inhomogeneities of the magnets and the path length effects due to the relatively large beam divergence are corrected by in-beam spiral coils, spark-erosion cut from Aluminum plates.The OFS coils are designed to reach a maximum field integral of 0.06Tm corresponding to a Fourier time of 0.16 nanosec at an incident neutron energy of 14.7meV.Apectral resolution of -0.2 mueV is obtained, to be compared to 2.2 meV for the same TAS conf … More iguration without Spin Echo.This Triple Axis Spectrometer with Spin Echo (TASSE) option can be installed on the conventional triple axis instrument in one and half day time.The spin echo polarisation is fully maintained when the momentum transfer is changed up to the maximum spectrometer values of Q-3.6 *^<-1>.The intensity loss factor of 50 due to the introduction of polarisers and increased distances is to be compared with the resolution gain factor of approximately 10^4.The performance of this new, high resolution TASSE option is demonstrated using the experimental data obtained on the quasielastic diffuse scattering near the order-disorder phase transition in KDCO_3.Here the first evidence for a dynamical Huang scattering has been obtained which may be viewed as a characteristic of a strain field mediated order-disorder phase transition.Furthermore the spin density wave in Chromium have been investigated as an example of antiferromagnetic spin echo experiment.The experiment on SrTiO_3 has been performed, where the problem of the central component' is reinvestigated using the thermal neutron spin echo spectroscopy.Preliminary results on finite energy transfer spin echo at DELTAE-6meV phonon mode in SrTiO_3 have been also obtained. Less