Bowman J David, Penttila S I
Los Alamos National Laboratory, Los Alamos, NM 87544, USA.
J Res Natl Inst Stand Technol. 2005 Aug 1;110(4):361-6. doi: 10.6028/jres.110.054. Print 2005 Jul-Aug.
We present a conceptual design for an experiment to measure the neutron lifetime (~886 s) with an accuracy of 10(-4). The lifetime will be measured by observing the decay rate of a sample of ultracold neutrons (UCN) confined in vacuum in a magnetic trap. The UCN collaboration at Los Alamos National Laboratory has developed a prototype UCN source that is expected to produce a bottled UCN density of more than 100/cm(3) [1]. The availability of such an intense source makes it possible to approach the measurement of the neutron lifetime in a new way. We argue below that it is possible to measure the neutron lifetime to 10(-4) in a vacuum magnetic trap. The measurement involves no new technology beyond the expected UCN density. If even higher densities are available, the experiment can be made better and/or less expensive. We present the design and methodology for the measurement. The slow loss of neutrons that have stable orbits, but are not energetically trapped would produce a systematic uncertainty in the measurement. We discuss a new approach, chaotic cleaning, to the elimination of quasi-neutrons from the trap by breaking the rotational symmetry of the quadrupole trap. The neutron orbits take on a chaotic character and mode mixing causes the neutrons on the quasi-bound orbits to leave the trap.
我们提出了一个用于测量中子寿命（约886秒）、精度达到10的负4次方的实验概念设计。通过观测磁阱中真空中受限的超冷中子（UCN）样本的衰变率来测量寿命。洛斯阿拉莫斯国家实验室的UCN合作团队已开发出一个原型UCN源，预计能产生超过100个/立方厘米的瓶装UCN密度[1]。如此高强度源的可得性使得以一种新方式进行中子寿命测量成为可能。我们在下文论证，在真空磁阱中有可能将中子寿命测量到10的负4次方。该测量除了预期的UCN密度外不涉及新技术。如果能获得更高的密度，实验可以做得更好和/或成本更低。我们给出测量的设计和方法。具有稳定轨道但未被能量捕获的中子的缓慢损失会在测量中产生系统不确定性。我们讨论一种新方法，即混沌清洗，通过打破四极阱的旋转对称性来从阱中消除准中子。中子轨道呈现出混沌特性，模式混合使准束缚轨道上的中子离开阱。
