Momentum Distributions in Quantum Liquids (Materials Research)

原子动量分布的测量可以提供关于单粒子密度矩阵的详细微观信息。量子液体氦3和氦4提供了一个有趣且技术上简单的系统来研究动量分布。它们是液体的一个极端例子，其中量子零点运动和量子统计控制着行为。对散装液体进行了广泛的理论研究。对氦3 -氦4的混合玻色子-费米子系统也进行了计算。近年来，液氦3和液氦4在受限几何中的性质受到了广泛的关注。受限制的几何形状将液相很好地扩展到大块固体稳定的区域。表面固体层起着重要的作用，特别是在氦3中，在表面固体层中观察到铁磁体转变。Sokol教授建议使用高能非弹性中子散射来研究液氦4、氦3、氦3 -氦4混合物和受限几何中的动量分布特性。动量分布宽度的测量将用于研究粒子的局部环境作为温度和压力的函数。对于受限制的几何形状，动量分布也可以用来提取附着在表面的分子的信息。工作将使用阿贡国家实验室和联合王国卢瑟福阿普尔顿实验室现有的光谱仪以及阿贡新建造的专用光谱仪进行。

The measurement of atomic momentum distributions can provide detailed microscopic information on the single particle density matrix. The quantum liquids, helium three and helium four, provide an interesting and technically easy system in which to study the momentum distribution. They are an extreme example of liquids where both quantum zero point motion and quantum statistics dominate the behavior. The bulk liquids have been extensively studied theoretically. Calculations have also been made for the mixed Boson-Fermion system of helium three-helium four. Recently, the properties of liquid helium three and helium four in confined geometries have received considerable attention. The restricted geometries extend the liquid phase well into the region where the bulk solid is stable. Surface solid layers play an important role, especially in helium three where a ferromagnet transition has been observed in the surface solid layer. Professor Sokol proposes to use high energy inelastic neutron scattering to study the properties of the momentum distribution in liquid helium four, helium three, helium three- helium four mixtures, and in restricted geometries. Measurements of the width of the momentum distribution will be used to study the local environment of the particles as a function of temperature and pressure. For restricted geometries the momentum distribution can be used to extract information on the molecules bound to the surface as well. Work will be carried out using existing spectrometers at Argonne National Laboratory and Rutherford Appleton Laboratory, in the United Kingdom, as well as a newly constructed dedicated spectrometer at Argonne.