neutron polarising filters — theoretical comparison with supermirrors and Heusler alloy polarisers
neutron polarising filters — theoretical comparison with supermirrors and Heusler alloy polarisers
复制标题
中子偏振滤光片——与超级镜和赫斯勒合金偏振片的理论比较
DOI：
10.1016/s0168-9002(99)00951-1
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发表时间：
2000
影响因子：
1.4
通讯作者：
T. J. Hicks
中科院分区：
文献类型：
--
作者：
L. Cussen;D. Goossens;T. J. Hicks
目前有强烈的兴趣在气态3 He中子极化透射过滤器的发展。发展的关键领域是提高目前可实现的核自旋极化水平，π，在3 He气体和提高设备的可靠性。最近的工作已经确定了“质量因素”，可用于确定在各种实验条件下的最佳厚度的这种过滤器。确定了给定π的3 He偏振器的最佳品质因数。结果表明，最佳滤层厚度与π的关系很小，且总是近似地由无量纲表达式ρσλt=3.4给出，其中ρ为滤层中~ 3 He原子的密度，σ为波长为1 λ的吸收截面，λ为波长为1 λ的中子波长，t为滤层厚度。质量因子计算现有类型的中子极化器（超镜和Heusler合金单色器）作为仪器参数的函数。这些结果用于确定新偏振器的“收支平衡”点-新偏振器优于现有类型偏振器所需的π。定量讨论制度的有用性的不同偏振器类型的所有常见的仪器类型。
There is currently intense interest in the development of gaseous3He neutron polarising transmission filters. The key areas of development are increasing the currently achievable levels of nuclear spin polarisation, π, within the3He gas and improving the reliability of the devices. Recent work has identified “quality factors” which can be used to determine the optimum thickness of such filters under various experimental conditions. The best achievable quality factor for a3He polariser with a given π is determined. It is demonstrated that the optimum filter thickness depends only weakly on π and is always approximately given by the dimensionless expression ρσλt=3.4 where ρ is the density of3He atoms in the filter, σ is the absorption cross section at a wavelength of 1Å, λ is the neutron wavelength in Å and t is the filter thickness. Quality factors are calculated for existing types of neutron polariser (supermirrors and Heusler alloy monochromators) as a function of instrumental parameters. These results are used to determine the “break even” point for the new polarisers — the π needed for the new polarisers to outperform existing types of polarisers. A quantitative discussion of regimes of usefulness of the different polariser types for all common instrument types is presented.