Theory of inelastic scattering of cold neutrons from liquid helium
Theory of inelastic scattering of cold neutrons from liquid helium
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液氦冷中子非弹性散射理论
DOI：
10.1103/physrev.107.13
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发表时间：
1957
期刊：
影响因子：
--
通讯作者：
R. Feynman
中科院分区：
文献类型：
--
作者：
Michael Cohen;R. Feynman
测量从He II液体中散射的单能中子的能量损失，可以确定液体中基本激发(声子和轻子)的能量-动量关系。在固定角度的散射中，很大一部分是由单一激发的产生或湮灭引起的，在能谱上表现为尖锐的线条。从这些线的位置可以推断出激发的能量-动量关系。其他过程，如多次激发的产生或湮灭，提供了一个连续的背景，如果入射中子很慢(λ~>；4A)和氦冷(T<；2°K)，则发生的速度可以忽略不计。总的截面数据可以通过产生单个激发来解释；根据先前提出的表示激发的波函数计算的理论截面在整个能量范围内与实验一致，在30%以内。在1°K时，由于声子和轻子的长寿命，离散谱中的线宽可以忽略不计。
A measurement of the energy losses of monoenergetic neutrons scattered from liquid He II would permit a determination of the energy-versus-momentum relation for the elementary excitations (phonons and rotons) in the liquid. A major part of the scattering at a fixed angle arises from production or annihilation of a single excitation and appears as sharp lines in the energy spectrum. From the position of these lines the energy-versus-momentum relation of the excitations can be inferred. Other processes, such as production or annihilation of multiple excitations, contribute a continuous background, and occur at a negligible rate if the incident neutrons are slow (λ~>4A) and the helium cold (T<2°K). The total cross-section data can be accounted for by production of single excitations; the theoretical cross section, computed from a wave function previously proposed to represent excitations, agrees with experiment over the entire energy range, within 30%. Line widths in the discrete spectrum are negligible at 1°K because of the long lifetime of phonons and rotons.