Hrant N. Yeritsyan

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.

Superconducting properties of YBa2Cu3−xFexOy ceramics with small x

Abstract The influence of iron doping on the transition temperature to the superconducting state has been studied in ceramic YBa 2 Cu 3− x Fe x O y (0≤ x ≤0.01) samples by means of AC susceptibility χ ′− i χ ″ measurements. A statistical character of the onset transition temperature to the superconducting state T c on depending on iron concentration ( x ) was found. Monotonously decreasing behavior for the intergranular weak link coupling temperature T m J depending on AC magnetic field amplitude h 0 was observed. The higher the x the higher the dropping rate of T m J was observed for relatively strong field. It is found that the dropping rate of T m J against x is essentially decreasing in the range 0.003 x x up to 0.01. Possible explanations of obtained results are discussed.

Comparative analyses of physical properties of natural zeolites from Armenia and USA

Dielectric permittivity, specific conductivity, luminescence and infrared absorption properties of natural zeolites from Armenia and the US were studied. Optical spectra and dielectric permittivity including specific conductivity are compared for samples of both origins. It was shown that measured properties determine clinoptilolite content in the sample. In the sample of US origin there were more impurities than in Armenian ones. In the samples of Armenian origin clinoptilolite properties are more prominent.

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.

Electron irradiation effects in doped high temperature superconductors YBa2Cu3−xMxOy (M = Fe, Ni; x=0; x=0:01)

The influence of irradiation by electrons with an energy of 8 MeV, at dose intervals between 1013 and 2×1018el/cm2, on the properties of impurity doped, high-temperature superconductor YBa2Cu3−xMxOy (M = Fe, Ni; x=0; x=0:01) ceramics has been studied.It has been established that, as the irradiation dose is increased, the onset temperature of the transition to the superconducting state (Tcon), and the intergranular weak link coupling temperature between granules (TmJ), exhibit an oscillation around their initial values of approximately about 1–1.5 K. This oscillation indicates that the process of radiation defect formation in HTSC occurs in multiple stages. It was also found that the critical current (Jc)decreases with an increase of the irradiation dose, and exhibits a local minimum at a dose of 8×1016el/cm2coinciding with minima for Tcon and TmJ at this dose. It was found that the introduction of Fe atoms to the ceramic decreases TmJ, while introducing Ni atoms decreases both Tcon and TmJ; it is suggested that this is a result of Ni substitution of Cu both in Cu2 plane sites and Cu1 chain sites. The introduction of Ni causes a large change in the intergranular critical current density, Jc. A critical irradiation dose is obtained (2×1018)after which all HTSC parameters strongly decrease, i. e. the superconductivity of HTSC is destroyed.

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.

Quasi-Chemical Reactions in Irradiated Silicon Crystals with Regard to Ultrafast Irradiation

This paper reports results from an investigation of the interaction of displaced Si-self atoms (I) and their vacancies (V), with impurities in crystalline silicon (Si), as induced by micro-second pulse duration irradiation with electrons at different energies: 3.5, 14, 25 and 50 MeV and pico-second pulse duration with energy 3.5 MeV. V-V, I-impurity atom and V-impurity atom interactions are analyzed both experimentally and as modeled using computer simulations. A process of divacancy (V2) accumulation in the dose-dependent linear region is investigated. The effect of impurities on recombination of correlated divacancies, and I-atoms that had become displaced from regular lattice points is estimated by computer modeling of an appropriate diffusion-controlled process. It is concluded that the experimental results can be interpreted quantitatively in terms of a strongly anisotropic quasi-one-dimensional diffusion of displaced I-atoms. In addition, a significant difference is found between the effects of pico-second duration electron beam irradiation, which causes the formation of A-centre (V + Oxygen) clusters, while when the beam is applied on a micro-second timescale, divacancies are created instead, although the electrons have the same energy in both cases.

The Use of Different Pulsed Electron Irradiation for the Formation of Radiation Defects in Silicon Crystals

This paper reports the formation of structural defects in the lattice of silicon (n-Si) single crystals, as a result of irradiation by different intensities and pulses of electrons. The samples were studied by means of Hall effect measurements of electro-physical parameters (specifically the concentration of the main charge carriers) as a function of temperature and radiation dose. The role of the radiation current density (pulse height) is discussed, which gives rise to a peculiar behavior in the electrical-physical properties of n-Si. In particular, thermal processes are found not to develop, due to the ultrafast (pulse duration in the range 10−12–10−13s) nature of the incident radiation, which causes an almost “pure” energy interaction to occur between the radiation and the atoms within the crystal, and the formation of cluster defects. A scheme for the time-scale of the formation of these radiation defects is presented. From the dose and temperature dependences of the concentration of main charge carriers, the radiation defects introduction rates were determined.