Ilia V. Bogoyavlenskii

Study of the phonon–maxon region of the liquid helium dispersion curve – the latest results

Abstract New detailed data on the temperature dependence of the dynamic structure factor of liquid helium covering wave vector range from 0.2 up to 1.2 A −1 and temperatures from 0.5 up to 2.22 K have been obtained. Pre-analysis of the data has confirmed our findings concerning the existence of peculiarity in the dynamic structure factor at 0.5– 0.6 A −1 and temperatures just below Tλ.

Neutron scattering determination of condensate in liquid 4He

Abstract The results obtained during the last years on the temperature dependence of the Bose condensate in liquid 4 He are presented. Measurements of the Bose condensate density n 0 are performed with use of a deep inelastic neutron scattering method. A comparison with the other data obtained by the inelastic neutron scattering method is given. One can see a good agreement with all n 0 s obtained from inelastic neutron data by the developed and improved methods employed by other authors.

Neutron study of liquid 4He S(Q,ω) at the phonon-maxon region

Abstract Neutron scattering data from experiments on the time-of-flight spectrometer DIN-2PI at the pulsed fast reactor IBR-2 are reanalysed. To fit the one-phonon part of S(Q,ω), a damped harmonic oscillator (DHO) function was applied taking into account the instrumental resolution. The resolution function was determined using 4He scattering data at the lower temperature 0.44 K. The inconsistency between S(Q,ω) data presented and those obtained earlier apparently results from the different analysis procedure.

Neutron scattering study of liquid helium. Analysis of new data

A new analysis of neutron scattering data obtained earlier for liquid 4He is presented. The experiments were made on the time-of- flight spectrometer DIN-2PI in the pulsed reactor IBR-2. The results are analyzed by using a consistent data processing technique including the representation of the dynamic structural factor S(Q,ω) with a constant wave vector Q. The one-phonon component of S(Q,ω) is approximated by using the damped harmonic oscillator function taking into account the instrumental resolution. It is shown that the experimental values of S(Q,ω) are in good agreement with the fitting model, i.e., have a simple one-component structure. The presented results indicate a peculiarity in the temperature dependence of S(Q,ω) for liquid helium in the wave vector region 0.5–0.8 A−1. Various explanations of such a peculiarity are discussed.

Data analysis of the neutron scattering on4He at T=0.44 K

The data of inelastic scattering of 2.062meV neutrons on liquid helium at temperature 0.44K are presented. Measureinents are performed at DIN-2PI spectrometer incorporated with IBR-2 pulsed reactor [1].

On a structure of superfluid helium-4 elementary excitation spectrum

Abstract New experimental data of the liquid helium inelastic neutron scattering are reported. With the help of two Gaussian fitting procedure it was shown that for wave vectors q>q0=0.48&-1, the sharp phonon-maxon-roton peak consists of two modes, thus, elementary excitation spectrum possesses a complex structure. We can assume that one of these modes belongs to the neutron scattering as on the usual, “normal” fluid, while the other mode being connected with the liquid excitations induced by the presence of the bose-condensate.

A discussion of the dispersion curve of energy excitations in liquid 4He

An investigation of the dispersion of excitations in a quantum liquid, superfluid 4He, is carried out. An attempt is made to systematize the published experimental data that indicate a substantially different nature of excitations with wave vectors corresponding to different parts of the dispersion curve of liquid 4He. Neutron spectroscopy data are analyzed in relation to a certain physical hypothesis concerning the formation of such a spectrum, and it is found that the majority of the known experimental facts can be explained in framework of that hypothesis. Particular attention is paid to a comparison of the experimental data obtained on the DIN-2PI time-of-flight spectrometer (at the IBR-2 Reactor, Dubna) with the results obtained at foreign research centers.

Analysis of liquid 4He neutron scattering data on the basis of the Glyde-Griffin model☆

Abstract We report results of the analysis of liquid 4 He neutron scattering data on the basis of the Glyde-Griffin model. A qualitative accordance of the experimental S ( Q , ω ) with the Glyde-Griffin model is observed.

Cryostat for neutron investigations on a large volume of liquid ho between 5.2 and 1.2K at pressures up to 30 bars

Abstract Investigation of liquid helium-4 by neutrons scattering methods demands special cryogenic equipment. The experimental conditions require a prolonged exhibition of the large liquid helium sample. Besides, helium-4 is one of the difficult subjects for cooling, as it possesses high heat content, the thermal capacity peak in λ-point, and the thermal conductivity in the superfluid state. A cryostat for the inelastic neutron scattering research is described. Cryostat permit to operate with the large liquid helium sample (2600cm 3 ) at the temperature range 5.2 − 1.2K and pressure up to 30 bars.