一种干净、明亮、用途广泛的中子衰变产物源
A clean, bright, and versatile source of neutron decay products
摘要：
本文介绍了一种新型的冷中子束站，用于研究自由中子β衰变的角关联。有了这个被称为PERC的射束站，“活性衰变体积”位于中子导管内部，带电的中子衰变产物被磁性引导到中子导管的末端。因此，在明确定义和精确可变的条件下，导向器在其出口处输送衰变电子和质子束，其可以与冷中子束很好地分离。这样就得到了一个通用的中子衰变产物源，它可用于中子衰变相关谱的各种不同的实验。与现有的中子衰变谱仪相比，使用PERC可以实现几个数量级的相空间密度的增益。中子束相关的背景是单独测量的PERC，和磁镜效应的带电中子衰变产物和边缘效应在活跃的中子束体积都强烈抑制。因此，新出现的衰变粒子的光谱和角分布将在10^-4的水平上没有失真，比现在所达到的要好10倍以上。
英文摘要：
We present a case study on a new type of cold neutron beam station for the investigation of angular correlations in the beta-decay of free neutrons. With this beam station, called PERC, the 'active decay volume' lies inside the neutron guide, and the charged neutron decay products are magnetically guided towards the end of the neutron guide. Hence, the guide delivers at its exit a beam of decay electrons and protons, under well-defined and precisely variable conditions, which can be well separated from the cold neutron beam. In this way a general-purpose source of neutron decay products is obtained which can be used for various different experiments in neutron decay correlation spectroscopy. A gain in phase space density of several orders of magnitude can be achieved with PERC, as compared to existing neutron decay spectrometers. Neutron beam related background is separately measurable in PERC, and magnetic mirror effects on the charged neutron decay products and edge effects in the active neutron beam volume are both strongly suppressed. Therefore the spectra and angular distributions of the emerging decay particles will be distortion-free on the level of 10^-4, more than 10 times better than achieved today.
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