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articulo para regalado

articulo para regalado - REVISTA MEXICANA DE F ISICA S 54(2...

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REVISTA MEXICANA DE F ´ ISICA S 54 (2) 10–14 NOVIEMBRE 2008 Optical effects by high energy electrons in additively colored KCl and KBr crystals R. Aceves*, R. P´erez-Salas, and T.M. Piters Centro de Investigaci´on en F´ ısica, Universidad de Sonora, Apartado Postal 5-88, Hermosillo, Sonora, 83190 M´exico, e-mail: [email protected], [email protected], [email protected] C. Vargas-Aburto and R.M. Uribe Program on Electron Beam Technology, Kent State University, 15825 Old State Road, Middlefield, OH 44062, USA, e-mail: [email protected], [email protected] Recibido el 12 de octubre de 2007; aceptado el 9 de agosto de 2008 Radiation effects of high energy electrons on pure and additively colored (AC) KCl and KBr crystals have been studied by optical absorption in the 200-800 nm range at RT. Besides the main F-center related absorption band at 553 nm, the F + 2 (670 nm) and F 2 (740 nm) bands (R 1 and R 2 centers in old notation) ascribed to F centers aggregates in additively colored KCl are clearly observed. After electron irradiation with energy of 1.0 MeV and doses of 100 kGy or 3.5 MeV and 180 kGy, the F + 2 and F 2 bands are strongly diminished, the intensity of the F bands is increased and its peak lightly shifted to low energy at 558 nm. In KBr, the related absorption band maximum for the pure and AC samples after irradiation shows the same peak position as the F-center absorption. For AC KBr the intensity of this peak versus accumulative doses shows a maximum around 300 kGy but in pure KBr the peak continuously increases. In contrast, KCl does not show such dependence on accumulative doses. For both samples, the electron irradiation induce at least two bands in the 210-300 nm (UV bands) range that has been related with hole centers (V bands). The results have been analyzed in terms of surface close F centers and alkali and halogen ions desorption processes. Keywords: Electron irradiation; radiation damage; alkali halides; color centers; F centers. Efectos por irradiaci´on con electrones de alta energ´ ıa en cristales puros y coloreados aditivamente (CA) de KCl y KBr se han estudiado a temperatura ambiente por absorci´on ´optica en el rango 200-800 nm. En cristales de KCl aditivamente coloreados, adem´as de la banda de absorci´on m´as importante, en 553 nm asignada a centros F, tambi´en se observan las bandas F + 2 (670 nm) y F 2 (740 nm) adscritas a agregados de centros F (centros R 1 y R 2 en la vieja notaci´on). Despu´es de la irradiaci´on con electrones con energ´ ıa de 1.0 MeV y dosis de 100 kGy ´o 3.5 MeV y 180 kGy, la intensidad de las bandas F + 2 y F 2 disminuye fuertemente y a la vez la intensidad de la banda F incrementa y su posici´on se desplaza ligeramente en direcci´on de menor energ´ ıa, a 558 nm. En KBr, despu´es de la irradiaci´on, el m´aximo de la bandas de absorci´on para los cristales puros y CA muestran la misma posici´on de pico que la banda de absorci´on relacionada con el centro F. Para
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