Neutron Scattering on Impurity Nanoclusters in Gel Samples

Abstract

Results of recent SANS experiments with impurity-helium gel (IHG) samples in He-II are presented. We estimate the mean size of the impurity nanoparticles that form the frame of the IHG samples and discuss the possibility to use IHG samples for the production of ultracold neutrons (UCNs) in He-II cooled to the temperature of a few mK, as well as the reflection of UCNs at any temperature. Our results indicate that the most promising materials for these purposes might be the heavy water gel samples with the mean sizes of D 2 O clusters of ∼ 8 nm and the heavy alcohol gel samples with the mean sizes of clusters of ∼ 15 nm.

Structural and phase transitions in nanocluster ethanol samples at low temperatures

“…The gel was prepared via condensation of a gas mixture of ethanol vapor and 4 He on the surface of superfluid helium He II cooled below 1.8 K. The samples were prepared in situ for subsequent studies by small-angle neutron scattering (SANS) at liquid helium temperatures in a special cryostat [18]. Initially the sample of the deuterated ethanol gel was prepared in the cell installed in the middle part of the cryostat [19], where we placed a pair of windows for visual control of the sample formation inside the quartz cell. The process of sample preparation continued for one hour and we got a spongy soft matter filling the whole cell (Fig.…”

On charged impurity structures in liquid helium

“…Such particles and systems have found many different applications: visualization of flows and quantum vortices in superfluid helium [2][3][4]; study of energy transfer phenomena in liquid helium [5]; development of new high-energy density materials [6][7][8]; investigation of tunneling reactions of hydrogen isotopes in impurity-helium condensates [9]; structural studies of rare gas, molecular deuterium and nitrogen nanoclusters [10][11][12]; study of cold neutron interaction with watergels [13,14]; synthesis of metallic nanowires in superfluid helium [15,16]. Laser ablation of metallic target in solid helium-4 allows to create so-called icebergs (helium crystals doped with metallic particles) remaining metastable below the melting curve [17,18].…”