Neutron β decay with Ultracold neutrons

本研究工作的目的是利用超冷中子（UCN）进行β衰变实验。高密度的UCN是UCN实验非常需要的。本文研究了超流氦（He-II）中的UCN产生。在此基础上，我们建立了一个spiral中子源，热和冷中子慢化剂与重水和氦-II低温恒温器的UCN生产。我们在新一代UCN源上成功地进行了UCN的制作和观测。我们通过在UCN探测器前放置一个完整的UCN反射镜并改变He-II的温度来证实UCN的观测结果。UCN计数如预期的那样变化。我们研究了UCN探测器的效率，然后在一个实验瓶中获得UCN的密度。当UCN能量小于100 neV，质子束功率为156 W时，该值为1.4 UCN/cm ^3。UCN的密度与格勒诺布尔的UCN密度是有竞争力的，格勒诺布尔是世界上最大的。通过改进质子束流功率、He-II恒流器和非中子慢化剂反射器的结构，我们预计UCN密度将大于10000 UCN/cm ^3。我们在《物理评论快报》上发表了这一结果

The aim of this research work was to carry out a β decay experiment with ultracold neutrons (UCN). High density UCN are highly desirable for the UCN experiment. We have studied UCN production in superfluid helium (He-II) with spallation neutrons. Based on this study, we built a spallation neutron source, thermal and cold neutron moderators with heavy water and a He-II cryostat for the UCN production. We succeeded in the UCN production and observation in the new generation UCN source. We confirmed the UCN observation by placing a complete reflector for UCN in front of a UCN detector and changing the temperature of He-II. UCN counts varied as it was expected. We studied a UCN detector efficiency and then obtained a UCN density in a experimental bottle. The value was 1.4 UCN/cm^3 for UCN energies less than 100 neV at a proton beam power of 156 W. The UCN density is competitive to UCN density at Grenoble which is largest in the world. We expect the UCN density will be larger than 10000 UCN/cm^3 by improvement of the proton beam power, the He-II ctyostat and aneutron moderator reflector configuration. We published the result in Phys. Rev. Lett.Ultracold NeutronSymmetry