Gilberto M. Ferraz

Application of jade samples for high-dose dosimetry using the EPR technique

The dosimeter characteristics of jade samples were studied for application in high-dose dosimetry. Jade is the common denomination of two silicates: jadeite and actinolite. The EPR spectra of different jade samples were obtained after irradiation with absorbed doses of 100 Gy up to 20 kGy. The jade samples present signals that increase with the absorbed dose (g-factors around 2.00); they can be attributed to electron centers. The EPR spectra obtained for the USA jade samples and their main dosimetric properties as reproducibility, calibration curves and energy dependence were investigated.

Thermoluminescence and opitical absorption of BaF2 crystals

Abstract Nominally pure and Dy-doped BaF2 crystals were investigated concerning their optical absorption (OA) and thermoluminescence (TL) properties. Peaks at 120—150 and 200°C were observed for a heating rate of 1.7°C/s. The TL response for γ-rays and the TL emission spectra were obtained for these peaks. Except for the purest crystal, all BaF2 crystals produced OA bands before irradiation typical of Ce3+ ions. After irradiation, Dy doped crystals showed bands due to Dy2+ ions. A nominally pure sample gave bands related to Ce2+ ions and photochromic centers of Ce3+ ions. and photochromic centres of Ce3+ ions. The correlation between some OA bands and TL peaks is discussed.

Radiation effects on BaF2 crystals

Abstract Nominally pure BaF2, BaF2: Sm (1 mol%), BaF2: Gd (0.05 mol%) and BaF2: Eu (0.02, 0.1 and 1 mol%) single crystals were investigated at room temperature with optical absorption (OA) and electron paramagnetic resonance (EPR) to understand the mechanism of radiation damage. Irradiation of the samples at room temperature with γ-rays resulted in the electron capture by trivalent impurity ions, Sm3+ and Eu3+, forming the divalent impurity ions. However, no noticeable change in the valency of Gd ions could be observed. One of the nominally pure BaF2 crystals showed a band at 6.10 eV both before and after irradiation, which is due to Pb2+ ions. On irradiation two additional bands at 4.25 and 5.58 eV are observed. A correlation is found between these bands and the EPR spectrum. These OA bands and EPR spectrum are attributed to Pb3+ ions.