Sergey K. Nikoghosyan

Radiation-modified natural zeolites for cleaning liquid nuclear waste (irradiation against radioactivity)

There have been comparatively few investigations reported of radiation effects in zeolites, although it is known that these materials may be modified substantially by exposure to ionizing radiation. Thus, by exposure to γ-rays or high-energy particles, the charge states of atoms may be changed so to create, and accumulate, lattice point defects, and to form structurally disordered regions. Such a technique may permit the creation, in a controlled fashion, of additionally useful properties of the material while preserving its essential stoichiometry and structure. Accordingly, we present an application, in which the cation-exchange capacity of a natural zeolite (clinoptilolite) is substantially enhanced, for the treatment/decontamination of water contaminated with radionuclides e.g. 134Cs, 137Cs and 90Sr, by its exposure to high-energy (8 MeV) electrons, and to different total doses.

The effect of electron irradiation on the optical properties of the natural armenian zeolite-clinoptilolite

Infrared (IR) absorption and luminescence in chemically and radiation-modified natural Armenian Zeolite (clinoptilolite) samples have been studied. The luminescence was studied in 390–450 nm and 620–710 nm wavelength bands, and the IR measurements were carried out in the 400–5400 cm−1 range. It is shown that the luminescence intensity depends on the content of pure clinoptilolite in the samples and, probably on the distribution of “passive” luminescence centers over Si and Al sites that became “active” under radiation or chemical treatment. The samples of electron irradiated clinoptilolite have higher luminescence intensity than the chemically and thermally treated ones. A decrease in the intensity of IR absorption bands at 3550 cm−1 and 3650 cm−1 was found after irradiation.

The effect of aging on the superconducting transition temperature and resistivity of Y-Ba-Cu-O ceramics after high temperature treatment

Some changes in superconducting transition temperature Tc and normal resistivity r of YBa2Cu30x ceramics are investigated as a result of the aging stimulated by high temperature treatment and slow cooling to room temperature followed by the storage under environmental conditions during 255 hours. It is shown that the changes of these parameters fall on three specific intervals of storage time ta. In addition, different types of aging processes: fast and slow ones are observed for the heat-treated samples. It is found that the fast processes are accompanied by a slight increase of r and Tc within the first interval of storage time ta (ta ≤ 162 hrs.), while the slow processes correlate with a sharp decrease of Tc and simultaneous increase of r within the second aging interval (162 hrs. ≤ ta ≤ 206 hrs.). It is revealed that the fast and slow aging processes result from the redistribution of atoms in intergranular weak and strong links, correspondingly. The probable reason of the observed results is the formation and coexistence of various structural phases including the semiconducing one.

Dielectric properties and specific conductivity of armenian natural clinoptilolite irradiated by electrons

The results of dielectric properties and direct current specific electric conductivity measurements in Armenian natural clinoptilolite samples are presented. Electron irradiation with energy 8 MeV and thermal treatment of samples are performed to elucidate possible enhancement mechanisms of clinoptilolite parameters. The results are discussed on the basis of new point structural defects formation and recombination of initial ones in samples. It was shown that the irradiation dose of 3·1016 el/cm2 is critical for natural zeolite structural change, which is manifested by significant changes in dielectric properties and other characteristics. The samples subjected to high temperature heating after electron irradiation, in comparison with an unquenched one, have a significantly higher (about an order of magnitude) value of specific conductivity.

Time Evolution Effect of Critical Transition Temperature in Electron Irradiated YBa2Cu3Oy Ceramics

The time evolution effect of onset transition temperature to the superconducting state T c on , intraand intergranular hysteresis loss peak temperatures T m g and T m J is investigated for YBa 2 Cu 3 O, ceramics, irradiated by a 4 MeV electron beam with doses of 10 14 , 10 15 , 10 16 and 10 17 electrons/cm at T = 300 K and subsequently aged at the same temperature for about τ a = 400 days. It is shown that the recoveries of T c on and T m g occur for all considered doses and the same is true for T m J in samples irradiated with doses up to 10 16 electrons/cm 2 . However, for the sample irradiated with a dose of 10 17 electrons/cm 2 T m J decreases rapidly with increasing τ a and finally achieves some stable value, which is significantly far from the initial one. The observed results are interpreted in comparison with our previous results on aging phenomena.

The influence of the bulk density on the intergranular superconducting properties of YBa2Cu3−xFexOy (0≤x≤0.01) ceramics

The influence of the bulk density of YBa 2 Cu 3-x Fe x O y (0 ≤ x ≤ 0.01) ceramics on the intergranular superconducting (SC) properties was studied using the temperature dependence of AC magnetic susceptibility measurements. It was found that the simultaneous variation of the samples density and the iron impurity concentration does not influence effectively the onset temperature of the SC state T on c . While only increasing of the samples density shifts the intergranular hysteresis losses peak temperature T J m to the lower values which connects with the decreasing of the Josephson magnetic vortices pinning role. It was established that the shielding capability and T J m display a plateau with x in the 0.003 < x < 0.007 region which is due to the monotonous decrease of the samples density. It was shown that the shielding capability at the T = 78 K for the sample with 3.8 g/cm 3 is two times higher than that for the sample with the density of 5.0 g/cm 3 . The possible interpretations of the observed results are discussed.

Effect of Direct Transport Current and Heat Treatment on Resistive Properties of Bismuth-Based Ceramic High-Temperature Superconducting Oxides of Various Compositions

The effect of direct transport current (I) and heat treatment on resistive properties of bismuth-based ceramic high-temperature superconducting oxides of various compositions is studied by temperature dependent resistivity (r) measurements at fixed points in the vicinity of liquid nitrogen temperature in the presence of Earths uncompensated magnetic field. It is shown that the observed results are significantly dependent on the sample preparation and post-processing conditions as well as on the measurement temperature. The results obtained are interpreted within the framework of the theory of Josephson weak links modified under the impact of self magnetic field of the sample’s transport current. An attempt is also done to find an analogy between the dependence of the characteristic parameters on the transport current in the case of heat treatment and on the dose when the samples are irradiated by various types of ionizing radiation.

The influence of DC transport current on the superconducting and normal properties of ceramic high-temperature superconducting Bi-based oxides after their heat treatment

The effect of the DC transport current (I) on the superconducting and normal properties of ceramic high-temperature superconducting bismuth-based oxides of different compositions was studied by temperature dependent resistivity (r) measurements at fixed points around liquid nitrogen temperature under the presence of Earths geomagnetic field. It has been shown that the observed results are significantly dependent on the sample preparation and post-processing conditions as well as on the measurement temperature.

The influence of hydrochloric acid treatment and temperature on the electro-physical properties of super-thin basalt fibers

Electro-physical parameters of super-thin basalt fiber (STBF) from Armenian basalt rocks are measured before and after hydrochloric acid treatment. It is shown that specific resistance and dielectric parameters of super-thin basalt fiber change essentially after hydrochloric acid treatment. The temperature dependence of these parameters was studied too. The probable cause of the change is an increase in the total amount of pores and modification of the share of pores of various sizes in STBF, followed by an increase of absorption of water molecules from the ambient medium. The results (in both alternating and direct electric fields) are interpreted within the framework of the dipole-relaxation mechanism of the polarization of water molecules in STBF pores.

The Features of Intragranular Irreversibility Lines in Y‐ and Bi‐Based Superconductors

The measurements of temperature dependence of AC magnetic susceptibility were used to study the influence of structural inhomogeneities on intragranular superconducting properties of YBa 2 Cu 3-X M X O Y (M = Fe, X = 0.005; Al, X = 0.01; Cr, X = 0.01), Bi 1.7 Pb 0.2 Sb 0.1 Sr 2 Ca 2 Cu 3 O γ and Bi 1.5 Pb 0.3 Sb 0.2 Sr 2 Ca 2 Cu 3 O Y ceramics. It is found that step-like regions are revealed on irreversibility lines (ILs) for superconducting granules. The steps on the temperature scale depend on sample composition as well as on the type of atoms substituted for copper. They range from 1 to 2 K for Y-based to about 5 K for Bi-based samples. Possible interpretation of the obtained results is presented.