The Sixth International Conference "Modern Problems of Nuclear Physics", September 19-22,2006 R MPNP'2006

One can conclude from our findings that the most probable model for 243nm absorption band and for 400 nm luminescence is the center of oxygen vacancy with two neighboring atoms of silicon and germanium (=Si-Ge=). We also find that not an essential change in intensity of 243nm absorption band is observed as the irradiation dose increases. Moreover, 400nm luminescence band shows decrease in intensity. The observed radiation-induced effects seem to related to y-radiation, which causes a change in local surroundings of initial defect state (=Si-Ge=) and lengthen thus bonds between Ge and Si (=Si —Ge=). In this case, depending on local surroundings there can be both vacancies, which are incapable to produce luminescence, and vacancies, which have ordinary bonds between atoms (=Si-Ge=) and become luminescence centers. In this picture, the absorption band in the vicinity of 243nm must present for both of the types of defects.

UZ0603140

COMPARATIVE STUDY OF RADIATION-INDUCED OPTICAL BEHAVIOR OF QUARTZ GLASSES AND SAPPHIRE CRYSTALS

Nuritdinov I., Islamov A.K., Amonov M.Z., Boboyerova S.G. Institute of Nuclear Physics, Tashkent, Uzbekistan

Different parameters of plasma in accelerators and fusion reactors, such as density, temperature, dynamics of relaxation, are often estimated by emission in the optical spectral range. So that optics of detecting devices (windows, lenses, etc.) should be transparent in the range of 170-1200nm. Their parameters, however, appear to be changed under radiation influence (fast neutrons, gamma-quanta etc). It may lead to misrepresenting of useful signal due to both transparency decreasing and undesirable radiation stimulated luminescence of optical material. In this connection comparative study of the radiation damage of optical absorption and luminescent behaviors of KU-1 quartz glass and sapphire crystals was undertaken with the aim to predict to what extent the properties of these materials may degrade in the field of radiation. The samples were bombarded with neutrons of the fluencies lO'MO20 cm"2 (neutron flux 1013 cm s"1, E>0.1MeV) and gamma-irradiated in the dose interval of 106-1010 Rad (60Co, E=1.25MeV, gamma dose rate 670R/s). It should be noted, however, that such a huge fluencies and dose couldn't be reached in real conditions. In the gamma dose interval mentioned sapphire crystals do not show any additional absorption bands. On the contrary KU-1 quartz glass exhibits the radiation-induced absorption band peaked at 215nm, the intensity of which is increased with gamma dose up to 5.108R with following saturation. At the same time the transparency in the spectral range of 300-900nm doesn't decrease significantly. Sapphire crystals show gamma-stimulated luminescence in the range 300-330nm while quartz glasses do not emit under gamma excitation at room temperature. Neutron bombardment leads to deep coloration of sapphire crystals but does not change the transparency of quartz glasses in the spectral range of 300-600nm. At the same time neutron irradiation causes the appearance of gamma-luminescence in both materials. Quartz glasses show two luminescence bands at 470 and 650nm, intensity of which is increased with neutron fluence and saturated at the fluence 1019cm~2. Two gamma-luminescence bands at 330nm (F^-centre) and

228 Section II. Radiation Physics of Condensed Matter The Sixth International Conference "Modem Problems of Nuclear Physics", September 19-22, 2006

420nm (F-centre) appear in sapphire crystals after neutron irradiation. Their intensity is increased with neutron fluence up to 1018 cm"2 and then decreased. It should be noted that gamma- luminescence intensity in sapphire crystals is ten times larger in magnitude than in quartz glasses is. From the date obtained one can conclude that both materials may be applied to design optical elements for nuclear sets with neutron flux less than 1012cm"V\ In these conditions the rate of accumulation of intrinsic radiation defects would be less and, consequently, the extent of degradation of transparency and luminescence appearance would depend on initial disordering of material.

UZ0603141

QUANTUM CRITICAL POINTS AND THEIR ROLE IN fflGH-Tc SUPERCONDUCTIVITY, STRIPE AND PSEUDOGAP FORMATION IN HOLE-DOPED CUPRATES

Dzhumanov S. Institute of Nuclear Physics, Tashkent, Uzbekistan

The discovery of the new copper oxide (cuprate) high-7^ superconductors (HTSC) and the intensive studies of the physical properties of these materials have led to the revolutionary era in condensed matter physics [1]. After this discovery, it has become clear that these high-7c cuprates deviate most strongly from conventional low-rc superconductors, both in the normal and in the superconducting (SC) state [1,2]. The breakdown of the well-known one-electron band theory, Fermi-liquid and BCS pairing theories (see Refs. [1, 2]) occurs in a wide range of the phase diagrams of the hole-doped cuprates, and the competitions between different ground states of the cuprates in a substantial region of the phase diagrams, lead to the occurrence of the distinct pseudogaps (PGs) and quantum critical points (QCPs) and to the stripe formation in these systems. The high-7^ superconductivity in the hole-doped cuprates occurs also in this region of their phase diagrams. Although much experimental and theoretical works have been carried out in the past two decades, they have not yet reached any conclusive understanding on the electronic phase diagrams of these high-Tc cuprates, and on the distinct QCPs and their role in high-j^ superconductivity, stripe and PG formation. The exotic properties of the high-rc cuprates and their understanding require radically new theoretical approaches and physical concepts. In this work, we discuss the possible origins of the QCPs, metal-insulator transitions, PGs, dynamic (metallic or SC) and static (insulating) stripes, and high-re superconductivity in hole-doped cuprates. We develop the new and more pertinent theoretical approaches and methods for studying the quantum criticality and the existence of the distinctly different QCPs in these materials at the strong electron-phonon interactions and to examine the role played by the QCPs in high~rc superconductivity, PG behavior and stripe formation in the cuprate HTSC. We obtain quantitatively the real and adequate phase diagrams of the hole-doped cuprates and focus on key questions related to the entire phase diagram of the different cuprates, from underdoped to heavily overdoped region. This should allow us to check whether the usual Fermi-liquid and BCS pairing theories valid also for the cases of the intermediate and strong electron-phonon coupling regimes or they break down. We show that the QCPs, dynamic and static stripes, PG behavior and unconventional high-rc superconductivity are emerged in hole-doped cuprates in the strong

. 229 Section II. Radiation Physics of Condensed Matter