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

这个小企业创新研究的第一阶段项目是开发一种改进的方法来极化冷、热和超热中子。人们早就认识到，中子可以通过致密的、自旋极化的气态3He靶而发生极化。因为极化3He的热中子吸收截面在反平行自旋情况下比在平行情况下大10,000倍，一个足够厚的极化3He靶有效地传输处于一个自旋状态的中子，并强烈衰减其他自旋状态。这种类型的透射偏振器比目前可用的反射偏振器（“超镜”）有几个优点。与超镜偏振器不同，3He滤波器可以应用于超热中子，并且可以用作许多标准中子散射仪器的偏振分析仪，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。以前有两种方法用于3He的自旋极化。第一种是与光抽运碱（铷蒸气）进行自旋交换，这是一种极其缓慢的方法，需要一天的时间才能实现完全极化。第二种方法是直接泵送亚稳氦，这种方法只在非常低的压力（2托）下进行过尝试，因此必须有额外的能力来给极化气体加压。直接法的物理性质与准分子激光的物理性质有很大的相似之处，而准分子激光的物理性质在科学研究实验室有着悠久的历史。本项目将开发一种高压（1atm）高极化（75%）3He中子自旋滤波器，用于极化中子散射等领域。该设备将采用一种专有方法，在高压下快速直接地极化3He，避免了其他方法面临的问题，并且是一种低成本、可靠的设备。这个概念的可行性将在拟议的第一期计划中进行详细研究。第二阶段将包括中子自旋滤波器的原理验证演示。接下来将是私人资助的第三阶段计划，其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中子和超热中子极化。这种偏振器将在美国、加拿大、欧洲和亚洲的热中子和超热中子设施中得到应用，作为现有中子散射仪器的升级版。其他应用也存在于核物理学和磁共振成像中。

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.