Studies of Polarized Atomic Hydrogen

极化原子氢（H*）由于大量子效应，即使在零K时也处于气相，如果具有足够密度的原子氢在低温下冷却，预计会出现玻色凝聚。原子氢气在极低温度下的量子性质的研究引起了人们的广泛关注。在本研究项目中，我们主要研究了以下内容：(1)研究了液氦表面吸附的二维（2-D） H*，并研究了获得二维超流动性的可能性，即Kosteritz-Thuoless跃迁。在这个实验中，原子氢是由低温放电产生的，并被引入到位于高磁场的缓冲体中，并在那里极化。一些储存的H*通过毛细管进入样品细胞。在样品池中，我们制备了一个小的冷点，H*被吸附和冷却。为了减少电池表面的复合，在电池表面涂覆了一层超流He膜。我们能够将表面密度为10^<12>/cm^2的二维H*冷却到85 mK。我们发现，向二维系统倾倒的复合热的百分比远低于1.4%。我们研究了二维H*与液态He之间的热耦合机制。(2)研究了氢原子在He气体中的自旋扩散常数。这个问题提供了一个独特的机会，在微观基础上研究极低温度下的气体动力学。利用Carr-Purcell-Meiboom-Gill法观测了近零场共振下的自旋回波，确定了氢在He气体中的扩散常数，并推导了扩散截面。我们确定了H和He之间相互作用势的细节。(3) H的核自旋也是极化的，称为H**。讨论了将H*应用于基本粒子物理的可行性。

Polarized atomic hydrogen (H*) is in a gaseous phase even at zero K due to the large quantum effects and is expected to show Bose condensation if atomic hydrogen with a sufficient density is cooled at low temperatures. Studies of the quantum nature of the atomic hydrogen gas at very low temperatures have attracted much attention. In this research project, we studied the following: (1) We studied the 2-dimensional (2-D) H* adsorbed on liquid helium surface and investigated the possibility to obtain the 2-D superfluidity, so called Kosteritz-Thuoless Transition. In this experiment atomic hydrogens were produced by a cryogenic discharge and were introduced into the buffer volume located in a high magnetic field and were polarized there. Some of the stored H* was introduced through a capillary into a sample cell. In the sample cell we prepared a small cold spot where H* were adsorbed and cooled. In order to reduce the surface recombination the surface of the cell was coated with a superfluid He film. We were able to cool the 2-D H* with a surface density of 10^<12>/cm^2 down to 85 mK. We found the percentage of the recombination heat dumped to the 2-D system was much less than 1.4%. We investigated the thermal coupling mechanism between the 2-D H* and the liquid He. (2) We studied spin diffusion constant of atomic hydrogen in He gas. This problem offers a unique opportunity to investigate the gas kinetics at very low temperatures on a microscopic basis. By using the Carr-Purcell-Meiboom-Gill Method to observe spin echoes nearly at zero field resonance, we determined diffusion constant of H in He gas and deduced a diffusion cross section. We determined the details of interaction potential between H and He. (3) The nuclear spin of H is also polarized and called H**. We discussed the feasibility of applying H* for elementary particle physics.