Gamma Radiation Effects on Some Properties of YBCO

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L. LUO, Y.H. ZHANG, S.H. HU, W.H. LIU , G.L. CHANG Shanghai Institute of Metallurgy, Academia Sinica *Shanghai Institute of Nuclear, Academia Sinica






ABSTRACT Radiation effects of polycrystalline YBCO bulk sample irradiated by 6 0 Co y-rays from a dose of 1x10 6 up to 7.SxlO9 rad at room temperature on critical temperature and critical current were investigated. IR spectrum was also used to study the mechanism of the irradiation. A considerable dependence of these parameters upon irradiation dose was observed. No significant effects on critical temperature were found, but the critical current in zero magnetic field changed greatly. It shows a tendency to decrease with the increase of the irradiation dose except for a slight increase with the dose less than about 2x10 7 rad and no simple relations between critical currents and irradiation doses was found. A typical case is that the critical current is reduced to about 60% when the dose reaches 5x109rad, but the dependence of critical currents on magnetic field shows that the critical currents are higher than that of the unirradiated one in the range of magnetic field higher than 100 Gauss and decrease more slowly in magnetic field compared with the unirradiated one. The results indicate that the defects produced by y-ray irradiation are benefit to flux pinning in higher fields. IR spectra analysis reveals that the intensity of the peak responsible for the Cul-O 1 chain vibration is decreased, indicating that the bond of the Cul-O 1 may be partly broken through collision process of the Compton electron produced by the y-ray. This effect probably gives currents. rise to decrease of the critical INTRODUCTION Since the discovery of high-Tc superconductors [i], many experiments have been done on the radiation effects [2-6]. It is likely one of the first application of high-Tc superconductors will be in the fields of electronic devices. A highly desirable property of such materials, especially for the applications in satellites and other systems operating in the environment of outer space, is resistance to high-energy ionizing particles and radiation such as y and x rays. On the other hand, from the material scientist's point of view, radiation effect can be used to generate finely dispersed defects which form the pinning centers of the magnetic flux in high-Tc materials and in turn are benefit to current carrying devices. Gamma radiation effects on critical temperature, resistivity and microwave signal of YBCO have been investigated by many researchers [3-51, while no research was found to our knowledge to report the effect of y irradiation on critical current. These work demonstrate that there were no significant effects on Tc [3,4), but the resistivity at 273K changed slightly [4]. It was also suggested that the primary effect of y-ray irradiation would be the breaking of Cu-O bond through an electronic process [4], but no experiment was carried out to confirm it. Mat. Res. Soc. Symp. Proc. Vol. 2