SOLID STATE RADIATION PHYSICS LABORATORY

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RESEARCH AREAS

A large volume of investigations were carried out for more than 35 years which include:

1. Influence of irradiation on the main properties of silicon and silicon-dioxide-metal structures.

Silicon single crystal electrophysical and optical properties were studied before and after irradiation by electrons with energy 8 MeV and 50 MeV.
Point defects and clusters formation was identified in silicon and their influence on the specific conductivity, Hall effect and optical absorption in infrared region were studied.

The brief results are as follows:

  • An anomalous dependence of specific conductivity and Hall effect with irradiation dose was observed. It was explained as “radiation ordering”, followed by disordering process.
  • A new mechanism of subthreshold structural defect formation phenomena under influence of Synchrotron radiation was developed. · “Radiation narrowing” of silicon forbidden gap was observed after fast electron influence. · It was shown that depending on interaction mechanism of irradiation with atoms of Si-SiO2-M structure on the semiconductor-dielectric interface are form “radiation surface states” with different nature.
  • A formation of radiation defects was observed on the silicon surface covered by SiO2 layer even in case when bombarding particles (arsenic ions) do not reach to the SiO2-Si interface although spite of they fall from the dielectric side. A new mechanism was suggested explained this effect.
  • “Self screening” effect was observed which is based on the distribution of surface centres by the groups. Tunneling mechanism is developed explaining the capture of carriers on the surface centers.
  • It is revealed, that the accumulation rate of the radiation surface states arising in Si-SiO2-M structure by electron irradiation depends on field electrode. Under Al electrode this rate about 3-5 times is higher than in case of Au, Ag, Cu, Ni, Zn electrodes.

2. Influence of irradiation on the superconducting properties of high Tc superconductors, study of dynamic and interaction of magnetic vortexes in high Tc superconductors.

  • It is established that the penetration ability of the ac magnetic field is much higher than the dc magnetic field. These experimental results can be explained by a model, offered by us, assuming that the diameter of Josephson vortices increases during its movement.
  • It was found that the real and imaginary parts of the ac magnetic susceptibility in non complete magnetic flux penetration regime are proportional to the time derivative of the magnetic field energy.
  • Temperature dependence of intragranular losses in frequency range from 2 Hz to 90 Hz shows that probably the behavior of Abrikosov vortices are similar to those of Josephson vortices.
  • It was established, that both impurity doping and radiation induced defects result in the identical phenomena in ceramic high Tc samples: Yttrium and Bismuth based.
  • It is found that superconducting properties in inter and intragranular mediums show an oscillation character with irradiation dose, and the temperature of formation intergranular weak bonds TmJ is much effected from irradiation than intergranular bonding temperature Tmg because of the TmJ is stipulated by processes of chained (bridge) sublattice of oxygen while the Tmg shows processes inside granular surface of the oxygen bonding.
  • It was shown that the further store of samples after irradiation stimulates their superconducting properties (aging effect), which depends on origin of the samples (impurity content, defect structure) and irradiation dose.

3.Influence of irradiation particularly, fast electrons on the A3B5 semiconductors (GaP, InP)

  • It was shown the existence of some “tailes” of density of states in GaP forbidden gap after irradiation, which is explaned by local deformations of a crystal lattice caused by simple radiation defects.
  • It is revealed, that the introduction of radiation defects in n-GaP more strongly changes the mechanism of scattering of free carriers, than doping by chemical impurity.
  • A new mechanism of scattering on "«frozen" phonons (deformations located near the point radiation defects) with participation of subzone Х3С is offered.
  • It is established, that in case of the large concentration in scattering radiation defects (at high doses of irradiation) in crystals GaP and InP are formed more termostable coagulations of radiation defects.
  • As a result of an irradiation in crystals GaP and InP the increase of photosensitivity and occurrence of photo memory is revealed.

4. Influence of irradiation on the optical properties of garnet, ruby and corundum crystals

  • It was shown that the irradiation of corundum crystals by fast electrons causes stable radiation defects in anion sublattice, and in result color centers: F and F+ are formed.
  • A photoconduction was observed in corundum crystals after fast electron irradiation which was explained by jumping of conduction electrons on exited states of F and F+ centers.
  • An optical effect of small dose was found in corundum crystals which are result of ordering in initially crystal lattice; with irradiation dose increase the crystal comes to disordering.
  • It was established the increase of ruby crystals R-line photoluminescence irradiated by high dose fast electrons which is explained radiative or nonradiative transfer of energy from radiation-structural color centres to the ions Cr3+.
  • After irradiation of corundum crystals essential increase of reflection bands in vacuum ultraviolet region was observed in result of radiation stimulated desorption, which leads to the formation of restored Al phase.
  • Peculiarity of luminescence excitation spectra formations in the fundamental absorption region of irradiated corundum, ruby and garnet single crystals were established.
  • Radiation memory effect was observed in the irradiated by fast electrons corundum single crystals. The essence of this effect is in restoration of defined absorption bands (such as: F, F+, AliF) after thermal annealing and multiply irradiation by X-ray from synchrotron radiation.

5. Study of electrophysical and optical properties of Armenian natural zeolites (clinoptilolites) and influence of electron irradiation on these

  • An enhancement of electro-physical and optical properties of natural Armenian zeolite-clinoptilolite samples was obtained by means of radiation modification due to optimization irradiation dose and intensity. It was shown that the electron energy of 8MeV and dose 5·1012 e/cm2 is optimum in critical change of sample parameters for the best application. At high irradiation doses (more 1017e/cm2) the sorption capacity apparently decreases up to degradation of zeolite lattice.
  • A laboratory-pilot installation on the basis of irradiated Armenian zeolite samples was created and tested in Armenian nuclear power plant for the treatment of radioactive liquid wastes. In result the radioactivity of Cs134 and Cs137 nuclides reduced 1750 times wile non-modified natural zeolite reduces it by 80 times at the same conditions.

6. Simulating space condition and their effect on materials and devices intended for application in space

SUMMARY OF THE PROJECT
In this project it is proposed to develop and construct a Cosmic Space Imitator Installation and to investigate the influence of Space Factors on the properties of semiconductors (currently one of the most widely applied materials in the Space technology), High Temperature Superconductors (HTS), which are new, but proved to be very promising in Space applications and other materials and devices which are interesting for partner participants.

Stages of the Project

  • Construction of the vacuum chamber for modeling the factors of near Earth Space environment.

    The installation for imitation of space environment on the distance of 30-50 thousand km (I radiation belt of the Earth) will be constructed using developed drawings and will have the following parameters:
    • Chamber Volume -- 1,2 м3 ;
    • Solar ultra-violet radiation;
    • Electron beam with energy up to 10 МeV;
    • Vacuum 10-6 - 10-7 tоrr;
    • Temperature 80-100 K;

    Thus, this will allow accelerated testing of materials and products intended for Space applications as well as development of appropriate recommendations for their applications.

  • Study of material properties exposed to various doses and intensities of electron irradiation with measurement of electro-physical and optical parameters taking into account post radiation annealing and “aging”.

7. International grants

The Laboratory team has conducted 4 projects funded by international grant-making organizations on physical properties of solid states and zeolite study. Benefits offered by this working model among others include financial stability and improved international collaboration.
The names of these projects and address in the Internet are below submitted:

A-001 (http://www.istc.ru/ISTC/sc.nsf/html/projects.htm?open&id=A-001)
Development and Adoption of Radiation Technologies on the Base of the Radiation-Physical Center of YerPhI.

A-102.2 (http://www.istc.ru/istc/sc.nsf/html/projects.htm?open&id=A-102.2)
Order-Disorder Transitions in Gauge and Spin Systems and "Memory" Effects in Solid States

A-485 (http://www.istc.ru/istc/sc.nsf/html/projects.htm?open&id=A-485)
Efficient Treatment Of Radioactive Liquid Waste By Zeolites Modified Through Chemical and Radiation Methods

A-1229 (http://www.istc.ru/istc/sc.nsf/html/projects.htm?open&id=A-1229)
Simulating Space Conditions and Their Effect of Materials and Devices Intended for Application in Space

Now the laboratory is working on a project entitled “Simulating Space Conditions and Their Effect of Materials and Devices Intended for Application in Space”, funded by International Scientific and Technical Center (ISTC).
The aim of this project is to study the influence of irradiation (electron with energy 8-10MeV and solar ultraviolet) on the main properties of materials and devices under conditions of Vacuum 10-6Torr., Temperature 100K. When the Project is finished, the laboratory will have a Space simulating Chamber with mentioned above parameters.
Thus, the Project will offer the possibility to obtain valuable fundamental scientific information regarding the Space conditions effect on the materials and devices. There are about 30 participants in this project: doctors and candidates of physics, engineers and technicians.

Areas for studies are planned as follows:

  • Studies of radiation influence on adsorbing, electrical-physical and optical properties on Armenian natural zeolites.
  • Joint projects with Scientific Centers in Armenia, NIS and foreign countries.
  • Participation in Various International scientific-technological activities supported by international grant-making bodies.
  • Simulating Space conditions and their influence on the properties of materials and devices intended for application in Space.

Infrastructure

It has to mentioned that thank to the financing from contractual projects the laboratory currently boasts 3 storied building with 500 m2 total area hosting labs and offices, special facility for 2 linear accelerators with 4 and 8 MeV energies, local library, seminar-hall, special rooms with equipment for optical, electrical-physical studies, small experimental hall for vacuum chamber installation simulating near Earth Space conditions: electron and solar irradiations, vacuum and low temperature.

Collaboration

The Laboratory was and is collaborating with industrial and scientific organizations both locally and internationally. Among them: Yerevan State University, Yerevan Engineering University, Byurakan astrophysical Observatory, Jewelry plant, Industrial associations Posistor, Transistor, Sirius factory. Joint experiments were carried out with Nuclear Physics Institute in Novosibirck, Leningrad State University, Physics Institute after Lebedev in Moscow, Ukrainian Physics Institute, Kiev, Tbilisi State University, Leipzig University, HASYLAB, University of Rome etc.