SBIR Phase I: A High Pressure Polarized 3He Neutron Spin Filter

这个小型企业创新研究第一阶段的项目是开发一种改进的方法来极化冷、热和超热中子。人们很早就意识到，中子通过致密的、自旋极化的气态3He靶可以被极化。由于极化3He的热中子吸收截面在反平行自旋情况下比平行情况下大10,000倍，所以足够厚的极化3He靶有效地传输处于一个自旋态的中子，并强烈地衰减其他自旋态的中子。这种类型的透射式偏振器与目前可用的反射偏振器(超级反射镜)相比具有几个优点。与超镜式偏振器不同，3He滤光片可用于超热中子，并可用作许多标准中子散射仪器的偏振分析器，包括目前在私营部门有大量应用的小角中子散射(SANS)光谱仪。以前有两种方法用来使~3He自旋极化。第一种是与光抽运的碱性物质(Rb蒸气)的自旋交换，这是一种极其缓慢的方法，需要长达一天的时间才能实现完全极化。第二种是直接抽运亚稳态~3He，这种方法仅在非常低的压力(2托)下尝试过，因此必须具有对极化气体加压的附加能力。直接法的物理原理与科学研究实验室有着悠久历史的准分子激光器有很大的相似之处。该项目将开发一种高压(1大气压)、高度极化(75%)的3He中子自旋过滤器，它将在极化中子散射和其他领域得到应用。该装置将采用一种专有的方法，在高压下快速、直接地极化3He，避免了其他方法面临的问题，并使之成为一种低成本、可靠的装置。这一概念的可行性将在拟议的第一阶段方案中进行详细研究。第二阶段将包括中子-自旋过滤器的原理证明演示。紧随其后的是一个私人资助的第三阶段计划，在该计划中将开发商业原型仪器。如果这项研究继续进行到第二阶段和第三阶段，3He中子自旋过滤器将允许有效的热和超热中子极化。这种偏振器将在美国、加拿大、欧洲和亚洲的热和超热中子设施中得到应用，作为对现有中子散射仪器的升级。在核物理和核磁共振成像领域也有其他应用。

This Small Business Innovation Research Phase I project is to develop an improved method for polarizing cold, thermal, and epithermal neutrons. It has long been realized that neutrons can be polarized by passing them through a dense, spin-polarized, gaseous 3He target. Because the thermal neutron-absorption cross section of polarized 3He is 10,000 times larger for the anti-parallel spin case then for the parallel case, a sufficiently thick polarized 3He target efficiently transmits neutrons that are in one spin state and strongly attenuates the others. This type of transmission polarizer has several advantages over currently available reflection polarizers (`supermirrors`). Unlike supermirror polarizers, the 3He filter can be applied to epithermal neutrons and can be used as a polarization analyzer in a number of standard neutron-scattering instruments, including Small Angle Neutron Scattering (SANS) spectrometers, which presently have substantial private sector applications. Two methods have previously been used to spin-polarize 3He. The first is spin exchange with an optically pumped alkali species (rubidium vapor) which is an extremely slow method, taking up to a day to achieve full polarization. The second is direct pumping of metastable 3He which has only been attempted at very low pressures (2 torr) and thus must have an added capability to pressurize the polarized gas. The physics of the direct method bears great similarity to that of excimer lasers with which Science Research Laboratory has a long history. This project will develop a high pressure ( 1 ATM) highly polarized (75%) 3He neutron-spin filter that will find application in polarized neutron scattering and other areas. The apparatus will employ a proprietary method for polarizing the 3He quickly and directly at high pressures, avoiding the problems faced by other methods, and making for a low cost, reliable device. The feasibility of this concept will be investigated in detail in the proposed Phase I program. Phase II will consist of a proof-of-principle demonstration of a neutron-spin filter. It will be followed by a privately funded Phase III program in which a commercial prototype instrument will be developed. If this research is carried over into Phase II and Phase III, the 3He Neutron Spin Filter will allow for efficient thermal and epithermal neutron polarization. Such a polarizer will find applications at thermal and epithermal neutron facilities in the USA, Canada, Europe, and Asia as an upgrade to established neutron-scattering instruments. Other applications exist as well in nuclear physics and in MR imaging.