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。氦3和氦4这两种量子液体为研究动量分布提供了一个有趣且技术简单的系统。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都主导着这种行为。块状液体在理论上已经得到了广泛的研究。对氦三氦四混合玻色子-费米子系统也进行了计算。近年来，受限几何结构中的液氦3和液氦4的性质引起了人们的极大关注。受限制的几何构型将液相很好地延伸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了铁磁转变。索科尔教授建议用高能非弹性中子散射来研究液氦四、氦三、氦三-氦四混合物中的动量分布特性，以及在受限几何条件下的动量分布。动量分布宽度的测量将被用来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与表面结合的分子的信息。将利用联合王国阿贡国家实验室和卢瑟福·阿普尔顿实验室现有的光谱仪以及阿贡新建的专用光谱仪开展工作。

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.