TITLE:
Neutron Back- and Front-Face Bragg Diffraction on a Thin Si Single Crystal Excited by Ultrasound
AUTHORS:
E. Raitman, V. Gavrilov, D. Mjasischev, Ju. Ekmanis, A. Hoser, T. Hoffmann
KEYWORDS:
Neutron Diffraction, Ultrasound, Pendellösung
JOURNAL NAME:
Journal of Modern Physics,
Vol.6 No.1,
January
21,
2015
ABSTRACT: In this
research project, we measured and analyzed the spatial distribution of neutron
beam Bragg diffracted from the front- and back-faces of thin Si single crystal
undergoing on ultrasound excitation. For the perfect crystal, it is shown that
when the acoustic wave amplitude is increased, the front-face peak position
remains unchanged and its value grows linearly. The values of ultrasound wave
amplitude were determined. The back-face peak becomes asymmetric and tends to
disappear. New types of Pendellosung fringes in the center of the diffraction
profiles were observed at the first time. It is supposed that in the perfect
crystal this effect may be due to the appearance of the new “sonic” extinction
length, depending on the amplitude of the ultrasonic wave. Thus, it leads to
the new interference interactions between neutron wave and ultrasonic phonons.
It is established that within the framework of the dynamical theory of the
neutron scattering, some asymptotic models valid for the case of Laue geometry
as well as Kato’s quasi-classical approximation can be applied in the case of
Bragg geometry also. Good agreement between experimental data and the theory
has been obtained.