Radiation damage in Mg<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Al</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Exposure of single crystals of Mg${\mathrm{Al}}_{2}$${\mathrm{O}}_{4}$ to fast neutrons and to Van de Graaff electrons with energies in excess of 0.35 MeV introduces an optical-absorption band at 5.3 eV with a 1-eV half-width. This band can be partially bleached at temperatures as low as 40 K and a shoulder at 4.75 eV develops concurrently. This bleaching treatment also partially destroys a previously reported $V$-type absorption centered at 3.2 eV. Subsequent exposure to ionizing radiation destroys the 4.75-eV band and restores both the 5.3- and 3.2-eV bands to their original intensities. Since this behavior is analogous to the interconversion of $F$ to ${F}^{+}$ centers in ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$, it is concluded that the 5.3-eV band is the principal optical transition of the $F$ center (two electrons trapped at an oxide-ion vacancy) and the 4.75-eV band is attributed to absorption by the ${F}^{+}$ center (one electron trapped at an oxide-ion vacancy). In electron-irradiated crystals the 5.3-eV absorption begins to anneal near 110\ifmmode^\circ\else\textdegree\fi{}C and is about 90% destroyed upon isochronal annealing (10-min pulses) up to 355\ifmmode^\circ\else\textdegree\fi{}C. Neutron-irradiated crystals behave similarly. Measurement of the threshold energy for damage by electrons at 77 K yields a displacement energy for the creation of ${\mathrm{O}}^{2\ensuremath{-}}$ interstitial-vacancy pairs of 59 eV. The defect yield drops off substantially with increasing temperature, and at room temperature the apparent ${\mathrm{O}}^{2\ensuremath{-}}$ displacement energy is 130 eV. Possible reasons for this strong temperature effect are discussed.

Перевод пока недоступен