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The RADEX pulsed neutron source based on a linear proton accelerator at the Institute for Nuclear Research, the Russian Academy of Sciences, has one vertical channel with a 4-m path length and three horizontal channels with path lengths of approximately 10, 20, 30, and 50 m. The source is characterized by an unconventional configuration: the target and the water moderator are located perpendicularly to the proton beam; as a result, the neutron spectrum is enriched with epithermal and cascade neutrons. Using the source, investigations in the fields of nuclear physics, condensed-matter physics and nanostructures can be performed. The results obtained using various path lengths of horizontal channels of the RADEX neutron source are presented. Test measurements are conducted and direct beam spectra for the horizontal neutron channels and neutron diffraction patterns of test samples are obtained. The resolution for different path lengths of the neutron source is determined. The possibility of performing phase analysis is demonstrated.

JETP letters 106(11), 733 - 738 (2017). doi:10.1134/S0021364017230011, The crystal structure of elemental Sn was investigated by synchrotron X-ray diffraction at ultra high pressures up to ∼230 GPa creating in diamond anvil cells. Above 70 GPa, a pure bcc structure of Sn was observed, which is stable up to 160GPa, until an occurrence of the hcp phase was revealed. At the onset of the bcc-hcp transition at pressure of about 160GPa, the drop of the unit cell volume is about 1%. A mixture of the bcc-hcp states was observed at least up to 230GPa, and it seems that this state could exist even up to higher pressures. The fractions of the bcc and hcp phases were evaluated in the pressure range of the phase coexistence 160–230 GPa. The difference between static and dynamic compression and its effect on the V–P phase diagram of Sn are discussed., Published by Springer, Heidelberg [u.a.]

Synchrotron X-ray diffraction studies of the structural characteristics of Ba3TaFe3Si2O14 langasite are performed at high hydrostatic pressures (up to 60 GPa) created in a diamond anvil cell. At pressures up to 20 GPa, the Mossbauer absorption spectra for 57Fe nuclei and the Raman spectra are recorded. Two structural phase transitions at P ≈ 5.5 and 20 GPa are observed. The first transition corresponds to the displacements of light oxygen atoms and to an increase in the local symmetry of 3f oxygen tetrahedra surrounding iron ions. The second one is accompanied by a pronounced change in the lattice parameter c, and the unit cell volume undergoes a stepwise drop as large as 8.6%. An appreciable decrease in the parameter c at the structural transition should result in a significant increase in the exchange coupling constants between iron ions in neighboring ab planes underlying the giant increase in the Neel temperature in this crystal at pressures exceeding 20 GPa.

This communication considers structural features of nanocrystals synthesized at high pressure consolidated mixed nanopowders. This system presents a pseudoalloy of mutually insoluble elements Fe and Cu, and contains pores. The study aims to demonstrate quasi-stable state of nanocrystals and factors preventing the aging. Mossbauer and X-ray analyses show a strong dependence of phase composition of Fe-Cu nanocrystalline pseudo-alloy on pressure and on aging duration. It is found pressure to coarsen phase inhomogeneity which exists initially in an as-synthesized Fe-Cu pseudoalloy. Aging duration is shown to affect the nanophase state in the same manner. It is agued that aside with typical parameters as grain size, density, phase composition of nanocrystalline substances one should know a prehistory of every sample: synthesis duration, temperature and pressure, which have a marked influence on physical properties of nanophase compacts. The Fe disorder in the Cu lattice revealed by Mossbauer spectra substantially depends on applied pressure.

A high-efficiency thermal-neutron detector based on ZnS(Ag)/LiF scintillator is described, which employs a new technique of signal pick-up with the aid of a light guide and avalanche photodiodes instead of optical fibers and photomultipliers. Results of tests on the RADEX pulsed neutron source are presented, in which neutron diffraction patterns of test objects have been obtained.

Synchrotron X-ray diffraction studies of the structural characteristics of Ba3NbFe3Si2O14 langasite were performed at high hydrostatic pressures (up to 60 GPa) created in a diamond anvil cell. The Mossbauer absorption spectra of 57Fe nuclei and optical absorption spectra were recorded at pressures up to 10 and 54 GPa, respectively. The cascade of structural phase transitions at pressures of about ~ 3, ~ 20, and ~ 41 GPa was discovered. The first transition corresponds to the displacements of light oxygen atoms and associated with an increase in the local symmetry of oxygen 3f tetrahedra surrounding iron ions. The volume drop at the first transition is about 1.5%. The second transition at ~ 20 GPa is accompanied by a pronounced change in the lattice parameters a and c, while the unit cell volume undergoes a stepwise drop by 7%. Significant decrease in the parameter c at the structural transition should result in a strong increase of the exchange coupling constants between iron ions in neighboring ab planes, which may lead to a giant increase in the Neel temperature in this crystal at pressures above ~ 20 GPa. At the third transition at about 38–44 GPa, only a small anomaly in the relation is observed, but this anomaly is accompanied by substantial changes in the optical gap and in the quadruple splitting parameter.