Perspective Plan

APPLIED PHYSICS REASEARCHES  DEPARTMENT (APRD)

PERSPECTIVE PLAN OF WORK (2018-2020)

Subjects of scientific research directions of the Applied Physics Researches Department

(A.Alikhanian National Scientific Laboratory)

Basic research

1. Experimental and theoretical studies in the field of radiation physics of solids (laser single crystals – corundum, garnet, semiconductor materials: silicon А³В⁵, high-temperature superconducting materials, ceramics, natural minerals, etc.).
2. Studies of changes in electro physical characteristics of semiconductor structures with p-n junctions and metal-insulator-semiconductor structures under the effect of various types of ionizing radiation (electron, proton, UV radiation, etc.).
3. Experimental study of luminescent properties of wide-band materials using synchrotron radiation within a wide spectral range (UV-VUV-X-ray).
4. Comparative study of defects in silicon irradiated by ultrafast high density electron pulses.
5. Vibrating wire technology in accelerator physics.
6. Radio- cryobiology and radioecology

Applied Research

1. Development of methods for obtaining and investigation of physical properties of new corrosion-resistant, thermostable and radiation-resistant nanostructured compositional thermo-regulating coatings for space materials science, mechanic engineering, chemical industry and medicine;
2. Development and creation of modern methods for the purification of radioactive liquid substances and radioactive contamination of the environment in the territory of the Armenian NPP using natural minerals (clinoptilolite, basalt).
3. Charged particle/photon beam transversal profile diagnostics using vibrating wire monitors.
4. Development of methods for obtaining and cryobiologic experimental investigation of coli K-12 strains: radioresistant BL-1114( Gam ^r -444 ) and radiosensitive AB – 2463. 
5. Developmentof welding processes of bimetallic materials for the manufacture of ultra-high vacuum components. 
6. Investigationof properties of perspective materials and devices in extreme conditions. The research suggests in-situ investigation of the phenomena caused by structural defects due to electron and ultraviolet (UV) irradiation in semiconductors (mainly silicon single crystal,”silicon in insulator”, Bi and Y based high temperature superconductor materials, HTSC, diamond like and silicate structures.
7. Spectroscopy of wide-gap materials in UV-VUV-X-Ray ranges. Investigation of excited-states structures in mixed configuration of pure yttrium aluminum garnet (Y₃Al₅O₁₂ – YAG), singly and doubly doped YAG with trivalent rare-earth ions, as well as in complex oxides such as LiNbO₃: TR^{3 +}, C12A7 (7CaO*12Al₂O₃).

Research of radiation resistance of heat-resistant solar coatings under the effect of UV   radiations in silicate solutions (Na₂O. nSiO₂, K₂O. nSiO₂, Li₂O^.nSiO₂ n=l-4,5).

Radiation stimulation of materials by protons (18MeV cyclotron)

• Radiation defect formation in semiconductor materials.
• Radiation-enhanced processes in biological environment.

 Development of a new beam profile scanner on the basis of vibrating strings at the experimental output of C18 cyclotron

Scientific and technical cooperation 

• Yerevan State University, Physics and Radiophysics departments, Armenia

• Lebedev Physical Institute, Moscow, Russia

• Tartu State University , Estonia
• Moscow State University, Department of Optics, Moscow, Russia
• Institute of Problems of Microelectronics Technology and High-Purity Materials, Chernogolovka, Russia
• Georgian Technological University, Tbilisi, Georgia
• Institute of Physical Research , Ashtarak , Armenia
• Synchronous Radiation Center ( CANDLE ), Armenia
• Institute of General and Inorganic Chemistry NAS, Armenia
• O.Paton Institute of Electric Welding, NAS of Ukraine
• Leibniz- Institut für Festkörper -und Werkstoffforschung (IGW), Dresden, Germany;
• Helmholtz- Zentrum Berlin, Germany;
• Ulsan National Institute of Science and Technology (UNIST),South Korea
• DESY Hamurg , Germany

         Institute of ArmBiotechnology Armenia

      Scientific Directions

• In-Situ Study of Phenomena Induced by Electron and Ultraviolet Irradiations in Crystals
• Two installations imitating near Earth space conditions ensuring 8МeV electron flow, UV-irradiation, high vacuum (10^-5 tor) and different temperatures (120K- 450K) were designed and constructed: a large one (VSC) with a volume of 1.2m³ and a small one (SVC) with a volume of 45 liters.
• In-situ measurements of electrical conductivity (s) of silicon single crystals (n-Si) were carried out in the vacuum simulating chamber (VSC). The experimental conditions were as follows: vacuum 10^-5 Torr, temperature 177 K, 8MeV electron irradiation, solar UV radiation which correspond to near Earth space conditions. The experiments were performed step-by-step with and without UV radiation.
• After the above preliminary measurements, the UV source was switched on; electron beam was turned on, and s was measured depending on the electron dose. The irradiation intensity was 1.6 · 10 ¹⁰el / sec · cm ² that is higher by a factor of 100 that that in the near Earth space satellite (LEO) orbits. Additional decreasing of s by a factor of 3 was observed after electron irradiation at a dose of 5.76 · 10 ¹² el / cm ² in the presence of UV irradiation. In the meantime, s was more than 5 times lower than dark value.

• The observed behavior of s is explained by the fact that UV excitation stimulates and heating suppresses the formation of radiation defects (RD) in n-Si silicon lattice structure, whereas in p-Si the situation is opposite.  This effect leads to the localization of electrons around the RD and hence, to the decrease of carriers mobility, i.e.to decrease in s. During this process new RD are formed and their redistribution takes place. As a result of these interactions RD complexes are formed which are stable at room temperatures and define the behavior of s in silicon.
• It was shown that the specific conductivity of silicon samples measured during the irradiation process and after irradiation, has different values; the first is much higher. The higher value of σ under the irradiation process is due to ionization mechanisms (Auger or other irradiation induced processes) that result in the formation of non-equilibrium carriers (hole-electron pairs). These carriers are accelerated in the electric field making additional contribution to the specific conductivity.

It is shown that during electron irradiation at room temperature in air, according to the performed measurements, in p- and n-Si type samples the specific resistance (ρ) changes at various rates depending on the radiation dose. Besides, in p-Si type samples a strong increase of ρ (compared to  n- Si  type)  is observed in the case of significantly higher irradiation dose, which means  that p- Si  type samples are more stable to irradiation.

Spectroscopy of wide-gap materials in UV-VUV-X-Ray ranges

• Using Vacuum Ultraviolet spectroscopy together with synchrotron radiations, a set of experimental data including spectra of excitation (35-330 nm), luminescence (130-750 nm) and luminescence attenuation kinetics of rare-earth ions in crystals at various temperatures was obtained for the first time.
• For the first time the structure of excitation states of mixed 4f^n-15d configurations of trivalent ions of rare-earth elements in YAG, LiYF₄, BaY₂F₈ crystals was investigated based on photoluminescence spectra. It was established that the presence of Cr^{3 +} impurity ions considerably reduced the creation of anion F-centers by high energy electrons in α-Al₂O₃:Cr^{3 +}, i. e. the doping was a “luminescent protection” against the formation of radiation defects.
• In irradiated and non-irradiated ruby crystals, a new type of quick luminescence was revealed at 4.6 eV (270 nm) energy. It was attributed to so called “cross-luminescence” and is connected with recombination of valence band electrons with holes in low-lying core levels.
• Interconfigurational 4f¹⁰5d ↔ 4f¹¹ transitions of the Er³⁺ ion in the YAG host were studied under both VUV photon (synchrotron radiation) and electron beam excitation. It was found that the lowest low-spin 5d level of the Er³⁺ ion has a rather large energy gap to the next lower 4f ²D(2)_5/2 crystal-field level, which results in a relatively low non-radiative transitions from this 5d level, leading to the appearance of weak spin-allowed 5d – 4f luminescence at low temperature. The lowest high-spin 5d level, from which spin-forbidden 5d – 4f radiative transitions could occur potentially, is situated only at ~500 cm^-1 above the ⁴D_1/2 Such close location allows fast depopulation of the 5d level resulting in the absence of spin-forbidden 5d – 4f luminescence and appearance of ⁴D_1/2 4f – 4f luminescence.

       Electro – physical and magnetic properties of HTSC materials

• It was found out, that in two similar HTSC Y-Ba-Cu-O samples irradiated with electrons at a certain dose a) in air and b) in vacuum, after simultaneous UV excitation, the critical flux J_c depending on storing period (one year storage at normal conditions) showed a minimum. Besides, in b) alteration of J_c, conditioned by weak Josephson links was more pronounced than in a), which means that the role of defects as pinning centers is more important.
• The measurement of criticalparameters ofHTSCsampleswas carried out by registration of their current-voltage characteristics using the known four contact Then the influence of cross-section transport current (I) on superconducting transition curves was studied in the presence of theEarth’smagneticfield for2 differentcompositionsof ceramicHTSC samples:Bi₂Pb₂Sb_2..5Sr₂Ca₂Cu₃O_x and Bi_1.7Pb_0.3Sr_0.3Ca_0.2Cu_3.5O_x. It was determined that in above mentioned samples, superconducting transition curves exhibit step-like behavior similar to those for multiphase samples. The detailed investigation of normal resistance of the samples depending on the transport current passing through their cross section at fixed external magnetic fields for different impurities allowed to develop conditions for the creation of a sensitive magnetometer with a simple structure.
• The influence of vortex-vortex interaction on the behavior of Josephson vortexes in ceramics  YBa₂Cu₃O_x high-T_c superconductors in  and  type magnetic fields was investigated by means of measurements of complex magnetic AC susceptibility    at frequencies 0.01 Hz and 0.5 Hz. The experiments showed that at 0.01 Hz the influence of vortex-vortex interactions on theand components was insignificant. An essential increase of these parameters depending on temperature was observed at 0.05 Hz when the influence of vortex-vortex interactions on these parameters became appreciable.
• The influence of 8 MeV electron irradiation at a dose between 10¹³ and 2«10¹⁸el/cm² on the properties of doped high-temperature superconductor YBa₂Cu_3-xM_xO_y (M=Fe, Ni; x=O; x=0,1) ceramics was studied. It was revealed that at increased irradiation dose, the onset temperature of the transition to the superconducting state (T_c^on) and the intergranular week link coupling temperature between granules (T_m^j) demonstrated an oscillation around their initial values of 2K. This oscillation indicates that the process of radiation in HTSC occurs in multiple stages. It was found that the introduction of Fe atoms to the ceramics decreases T_m^J, while introducing Ni atoms decreases both T_c^on and T_m^j; 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 J_c. A critical irradiation dose is obtained (2«10¹⁸el/cm²), after which all HTSC parameters strongly decrease, i. e. the superconductivity of HTSC is destroyed.

Study of the effect of ultrafast electron beam on non-equilibrium processes in semiconductors

Project summary

The behavior of electro-physical characteristics of silicon (Si) crystals at non-equilibrium states under ultrafast (pulse duration 4×10^-13 sec) 3.5MeV electron irradiation will be studied using AREAL facility of CANDLE Synchrotron research Institute. There are many works on the influence of electron irradiation from conventional electron sources (pulse duration a few microseconds, energy 3-10 MeV) on the silicon crystals properties, for example [1-4]. It is well known that irradiation with electrons of these energies mainly causes point pair defects in semiconductors crystals. However, no investigation (except our papers [5-6]) was carried out, even theoretical, on the influence of picosecond electron pulses on the properties of solid materials and devices made of them. Meanwhile, such investigations are interesting from both scientific and applied points of view (processes in Space environment, pulse nuclear reactors and so on). In our future investigations it is proposed to study electro-physical properties of silicon single crystals under pulse (τ=4×10^-13 sec.) 3.5-4 MeV electron irradiation taking into account both the pulse duration peculiarity and non-equilibrium hole-electron forming at direct beam influence, i. e. in-situ process, when minority carrier life-time plays significant role in creating structural defects.

RADIATION RESISTANCE OF THERMOREGULATING COATING

The developed coatings can be used in aerospace technology, construction and transport industries, pharmaceuticals.

Purpose, objective

• Thermoregulating coatings (TRC) of new generation are designed for both passive thermal control and thermal conditioning. With respect to the absorption coefficient, three types of TRC are developed: “white” (as <0.2-0.3); “gray” (as = 0.4 – 0.6); “black” (as> 0.9). The purpose and application of the developed coatings is not limited to nano satellites; in the future they will be indispensable for maintaining the thermal regime of any space objects, including satellites, stations, and return vehicles. Moreover, they could be used for thermal stabilization of terrestrial objects and technological processes, and to a greater degree of the processes occurring in vacuum, where there is no heat transfer by surrounding gases (convective heat transfer).

Technical specifications:

• The range of variation in emissivity, when the temperature of various types of coatings is stabilized, is 2 to 4 times.
• The range of temperature stabilization for coatings of various types is within -50 to +120 Celsius degree.

Development of Accelerator Diagnostic Methods

·        Vibrating Wire Technology in Accelerator Physics·        Vibrating Wire Sensors for photon beams of Synchrotron Light Sources. ·        These devices were developed, manufactured and tested. Due to very high sensitivity it was possible to use such sensors for discrimination of main photon beam from the steering radiation arising at beam pass over the edges of dipole magnet field. The method was implemented at APS ANL. ·        Vibrating wire sensors for measurements of very high energy photon beams. ·        These devices allowed to use synchrotron radiation of Synchrotron Light Sources after passing through the terminating flanges of the accelerator vacuum chamber. The method was implemented at APS ANL .·        Multiwire Vibrating sensors. ·        To avoid necessity to scan the vibrating wires across the beam profile, special multiwire modifications of Vibrating Wire Sensors were developed and tested. For example, 5-wire monitor was used in experiments at APS ANL. ·        Vibrating Wire sensors with large aperture·        One of the tendencies in proton beam accelerators for applied usage is to produce high current beams of large aperture. Measurement of low fluxes of particle beams is an urgent task here (beam “halo”). Beam halo is one of the causes of beam loss, and the activation of machine components that results from the halo scraping on the limiting apertures of the vacuum envelope in high beam-power proton accelerators. We solve this problem by developing a new type of VWM that consists of two mechanically coupled wires; one of them remains vibrating and serves as instrument to measure the strain of the second wire which is exposed to the beam. An advantage of the proposed monitors is that aperture of the monitor is equal to the length of the exposed wire and can be made as long as necessary. This wire is completely free and even can be made from dielectric material. The use of materials with extraordinarily high thermal conductivity can lead to reducing the monitor’s response time, which is very desirable in some cases.·        A prototype of such a Large Aperture monitor with 60 mm long exposed wire was developed and tested on Electron beam of Yerevan Synchrotron Injector in 2010-2011·        Proposal for neutron beam diagnostics

• The principle of operation of Vibrating Wire Sensors is based on the measurement of the change in the frequency of vibrating wire, which is stretched on a support, depending on the physical parameters of the wire and environment in which oscillations take place.

·        Proposal on usage of Diffusive Radiation ·        A proposal on the use of Diffusive Radiation as Accelerator beam diagnostic tool is prepared. This radiation originated by the passage of charged particles through a randomly inhomogeneous medium. One of the important properties of Diffusive Radiation is that the maximum of emission takes place at large angles from particle velocity direction.·         Thermophysics·        Thermal analysis of sectional cylindrical furnaces ·        Analysis of rectangular furnaces  Vibrating Wire technology in Engineering·        VW Catharometer

• Accumulated considerable experience on creation of sensors on the base of vibrating wire including new methods of fixation of wire ends by hard-alloy clips and decoupling of degrees of freedom on the free end of the wire allowed achieving unprecedented accuracy and resolvability when measuring the wire tension.

Modeling of SpaceBiology problems (CrioRadioBiology)

In connection with the expected launch of the cyclotron, several projects were prepared for submission to the State Committee for Science, but they were not financed. However the leadership of the Institute of Synchrotron Research “CANDLE” is of interest. As a result, a new theme was formed, so called “Space Biology” or Cryoradiobiology. This direction became the object of intensive development for the last two years. Its goals are: (i) to evaluate the effects of low temperatures on a number of bacterial cultures including such classical objects of radiobiological studies as strains of bacteria E. coli; (ii) to use them as an object of irradiation with electron beams of different energies using AREAL accelerator of new generation (CANDLE), and compare the obtained results with the data we obtained earlier using 7.5 MeV microtron (YerPhI); (iii) to use irradiation at ultra-low temperatures (liquid nitrogen temperature). The results of the performed works are presented in the 2017 year report; here we just emphasize an interesting preliminary information, namely: correlation between the radiosensitivity and cryosensitivity of the tested strains of E. coli. At present, the works are at the stage of accumulation the statistical data to confirm the reliability of the obtained results. We emphasize once again that in the literature there are no data on this subject.

Radiobiology. A separate area of ​​research in this direction is purely radiobiological studies of the effects of beams of different particles on bacterial cultures. In particular, the problem of obtaining mutant strains of cultures capable of utilizing xenobiotics is of great interest. The purpose of such studies is to increase the target activity of these cultures. According to the literature data, the yield of mutants increases when passing from gamma beams to heavy ions. Since the production of highly active strains with the desired target activity is of great interest, studies on electron and proton beams are very promising. From this point of view we hope that it is possible to conduct appropriate experiments with 18 MeV protons (using cyclotron after its start-up). If necessary, the prepared offer can be submitted for consideration. In addition, it should be noted that similar experiments can be carried out with neutron beams using the Pu-Be source available in the Isotope Research and Development Division. Unfortunately, the intensity of the beam of this source is very small, and the preliminary results of our experiments have shown the need for variations in the technical conditions of the performed experiments. It is difficult to say whether it is possible to achieve tangible results by increasing the exposure time. However, it is known that under the suitable irradiation  conditions, the peak of mutants yield, for example, for the cells of E. coli (Lac^–– mutants) locates apart of the death peak on the graph, which gives a real possibility of their isolation