INELASTIC NEUTRON-SCATTERING STUDY OF EXC ITATION SPECTRUM IN LIQUID-HE-4

A complex multicomponent structure of the excitation spectrum of liqui d He-4 is revealed. A phonon spectrum region of liquid helium in the n ormal phase displays two components of slow neutron scattering intensi ty - a narrow component (0s) and a broad one (w). A maxon-roton region of the spectrum contains only a single broad component w. In the supe rfluid phase of liquid helium the latter pattern is supplemented by a narrow component, the intensity of which increases sharply with decrea sing temperature, while that of the broad one, on the contrary, decrea ses rapidly. Thus the excitation spectrum structure undergoes substant ial changes under the normal - superfluid phase transition, and also o n transition from phonons to maxons in the both phases. On the whole, the results obtained are in qualitative agreement with the model of ex citation spectrum formation in liquid helium proposed by Griffin, Glyd e, Stirling in a few last years. However, some of the pattern features cannot be treated in terms of the modern conceptions.