N Sasajima

Radiation damage in yttria-stabilized zirconia under Xe ion irradiation

Abstract Single crystals of yttria-stabilized zirconia were irradiated with 60 keV Xe ions in an electron microscope at several temperatures in the range 300–1473 K and the process of damage evolution was studied. Amorphization did not occur in the zirconia irradiated with 60 keV Xe ions up to the fluence of 1.8×1016 Xe/cm2 at all irradiation temperatures. In the specimen irradiated with Xe ions below 1073 K, defect clusters are formed first and then bubbles are formed. On the contrary, in the specimen irradiated above 1073 K bubbles are formed first and then defect clusters are formed. From the observation of bubble sizes and densities, temperature and dose dependence of bubble swelling were estimated. With increase in fluence or irradiation temperature the average size of the bubble increased resulting in greater values of swelling.

EELS ANALYSIS OF SIC CRYSTALS UNDER HYDROGEN AND HELIUM DUAL-ION BEAM IRRADIATION

Abstract Electron microscopy and Electron energy loss spectroscopy (EELS) measurement were performed in SiC irradiated with three kinds of irradiation mode, namely, H2+ ions, He+ ions, and a dual beam of He+ and H2+ ions. Amorphization occurred in SiC at a damage density from 0.2 to 0.4 displacement per atom (dpa) irrespective of ion species. High resolution EELS revealed that a large amount of implanted hydrogen is contained in the form of hydrogen molecules and C–H compound in bubbles. It is inferred that some of hydrogen atoms implanted in SiC are trapped in both Si- and C-sites. Most of the helium atoms implanted are considered to exist in bubbles.

Ion irradiation and annealing effects in Al2O3 and MgAl2O4

Abstract In situ observation of structural changes of Al2O3 and MgAl2O4 induced by Xe and He ion irradiations and successive annealing were performed in an electron microscope equipped with ion accelerator. By Xe ion irradiation amorphization occurred in both the materials and bubbles were formed in MgAl2O4. By He ion irradiation bubbles were formed in both the materials, but amorphization was not observed to a fluence of 1.8 × 1021/m2 (11 dpa). By annealing after the irradiation, bubbles began to grow large by coalescence at 1000°C in Al2O3, and at 900°C in MgAl2O4, respectively. Amorphization began to recover in both materials at these temperatures. In the case of MgAl2O4 amorphous region recovers completely to polycrystalline state at 1000°C, and in the case of Al2O3 to original single crystal, respectively. Pit formation and exfoliation also occur in both materials at about 1100°C.

In situ observation of damage evolution in TiC during hydrogen and deuterium ion irradiation at low temperatures

Abstract The processes of damage evolution in TiC crystals irradiated with 25 keV H2+ ions at 12 K and 28 K and 25 keV D2+ ions at 18 K and the effect of annealing after the irradiation were examined by in situ observation with an electron microscope equipped with an ion accelerator. Amorphization was confirmed in TiC irradiated with H2+ ions to a fluence of about 1 × 1021 H2+/m2 at 12 K, while no amorphization occurred in TiC irradiated with D2+ ions to a fluence of 4.5 × 1021 D2+/m2 at 18 K. No amorphization in D2+ irradiation is considered to be due to the difficulty of producing chemical bonding species which suppress the recovery of irradiation induced defects in comparison to H2+ irradiation.

Thermodynamic study on UPd3 3 and U(Pd0.85Rh0.15)3

The heat capacities of UPd3 and U(Pd0.85Rh0.15)3 were measured over the temperature range between 290 and 1500 K by direct heating pulse calorimetry, which is a direct method for heat capacity measurements. The measured heat capacities of UPd3 were smaller than the literature values up to 900 K. The heat capacities of U(Pd0.85Rh0.15)3, obtained for the first time, were a little larger than those of UPd3, but showed a similar temperature dependence. Since the oxygen partial pressures for the oxidation of UPd3 and U(Pd0.85Rh0.15)3 alloys were calculated from the heat capacities to be higher than that for MoO2(s), UPd3 and U(Pd0.85Rh0,15)3 are not expected to be oxidized during the irradiation of UO2 fuel.

Damage evolution in TiC crystals during hydrogen and helium dual-ion beam irradiation

Abstract The effect of He+ ion irradiation after H+2 ion pre-injection and of simultaneous 25 keV H+2 and 20 keV He+ ion irradiation at RT to 1423 K on the formation of bubbles in TiC crystals were examined. No amorphization occurred under these irradiation conditions. The formation and growth of bubbles produced by He+ ion irradiation is not enhanced by pre-injection of hydrogen atoms at RT. Bubbles are formed but do not grow appreciably by He+ ion, H+2 pre-injection and H+2+He+ dual-ion irradiation at room temperature. Remarkable growth and coalescence occurred during irradiation at high temperature of 1423 K.

Isotope effect between hydrogen and deuterium ion irradiation on titanium carbide (TiC) at low temperature

Abstract Damage evolution and amorphization in TiC due to He + , H 2 + and D 2 + ion irradiation at low temperature were examined by in-situ electron microscopy and EELS observation. He + ion irradiation at 20 K results in the production of a number of dislocation loops and bubbles but no amorphization. 10 keV H 2 + ion irradiation at 20 K causes amorphization at a fluence of about 4.5 × 10 17 (H + )/cm 2 , while 10 keV D 2 + ion irradiation at the same temperature produces amorphization at a fluence of about 9 × 10 17 (D + )/cm 2 . The difference in the fluences necessary for causing amorphization between H 2 + and D 2 + irradiation shows the isotope effect between H and D. H is more favorable for amorphization.