Low Temperature Physics: 39, 777 (2013); https://doi.org/10.1063/1.4821758
Fizika Nizkikh Temperatur: Volume 39, Number 9 (September 2013), p. 1001-1005 ( to contents , go back )
Small-angle scattering of neutrons from normal and superfluid liquid helium
P.L. Kapitza Institute for Physical Problem, 2 ul. Kosygina, Moscow 119334, Russia
ISIS RAL, STFC, Oxfordshire OX110QX, UK
Warwick University, Coventry CV47AL, UK
Received March 29, 2013
The results of experiments on small-angle neutron scattering in liquid helium in the range of temperatures of 1–5 K, performed on a neutron pulse source ISIS (England), are presented. The detailed measurements of angular distribution of scattered neutrons allowed one to observe an essential change in temperature dependence of the second moment of pair correlation function (the first derivative of angular distribution at small angles of scattering). At high temperatures the angular distribution of scattered neutrons follows the classical description of small-angle scattering, but at temperatures below the l-point a quantum behavior is observed neutron-scattering by quantum fluctuations. It is experimentally confirmed that in the whole temperature range the cross-section of neutron scattering at a zero angle is determined by the classical thermodynamic fluctuations of density.
PACS: 61.05.fg Neutron scattering (including small-angle scattering);
Key words: small-angle scattering of neutrons, statical structural factor, superfluid, quantum fluctuations.