Formation and Decay of Colour Centres in a Silicate Glasses Exposed to Gamma Radiation: Application to High-Dose Dosimetry

Effects of Electron Irradiation Upon Absorptive and Fluorescent Properties of Some Doped Optical Fibers

“…It is seen that IA in the Ce-free fiber is ~two times bigger than in the Ce-doped and Ce/Aucodoped ones. The other fact is that IA maxima are located near 400 and 500 nm in these two fibers, whereas the ones in the Ce-free one-at ~400 and ~600 nm, that is, in the range most probably attributing to well-known nonbridging oxygen-holes (NBOHCs) [26] (while the presence of other defect states in it-such as Si-/Al-defect centers cannot be excluded). Furthermore, it is seen from photos (b) and (c) that, in the Ce-doped and Ce/Au-codoped fibers, the core and adjacent core-cladding areas suffer darkening after β-irradiation, in the former, the effect being more pronounced.…”

“…The other would stem from Ce doping: it is seen from Figure 2 that such band does not exist in the reference Ce-free fiber. However, the irradiated Ce-free fiber demonstrates ~600 nm band, probably attributing the other type of NBOHCs [26], absent in both Ce-doped fibers subjected to irradiation: compare spectra 1-3 shown in Figure 2. The fact that the dose dependences of IA ( Figure 4) have different characters for the fibers points on different nature of the centers represented by bands 1 and 2.…”

“…As seen from Figure 5(d) and Figure 7(c), IA decreases almost exponentially at the beginning of bleaching. However, within the whole interval of optical bleaching, IA in bands 1 and 2 is seen to fade (in terms of negative AD at 543 nm illumination, see Figure 5(a, b), as well as in terms of shifting the transmission edge to shorter wavelength, at exposure the fibers to UV light, see Figure 7(a, c)), which obeys a "stretched exponent" law [26]. An explanation for this behavior can be not only complexity of the mechanisms involved at optical bleaching but also a fact of limited "penetration" of bleaching light into a fiber sample (especially in the case of 543 nm bleaching).…”

“…The processes, involved at irradiating the fibers with the result being rise followed by saturation of IA, described by the "stretched-exponent" law [14,24,26]), comprise: (i) creating of secondary carriers (holes h + and electrons e − ) in the core-glass matrix by β (primary) electrons and their trapping on such glass imperfections as Ce ions (Ce 3+ /Ce 4+ ), nonbridging oxygen centers, other centers associated with Al and P, and oxygen vacancies; (ii) direct h + …e − recombination (annihilation); (iii) thermally or/and radiatively activated recombination between the centers or defects that have arisen during and after β-irradiation. Concerning the role of Ce-doping, we assume that IA is produced via irradiation-induced reactions Ce 3+ +h + →Ce 3+ h + (→?Ce 4+ ) and Ce 4+ +e − →(?Ce 4+ e − )→Ce 3+ [26][27][28], implying Ce was in valences 3+/4+ in pristine fibers or/and being generated via irradiation. Note that determination of relative contents of Ce 3+ /Ce 4+ ions in the pristine state is hard and that at low Ce doping, mainly fluorescing Ce 3+ are formed in the core-glass, while at higher overall Ce concentration both Ce 3+ and Ce 4+ (nonfluorescing) ions can be present.…”

The Gray Institute open microscopes applied to radiobiology and protein interaction studies

“…This approach poses significant logistic problems due to (1) the fact that modern microscope bodies cannot be easily adapted to operate in a radiation environment (2) the formation of color centers in glasses 5,6 used in the various lenses in the microscope optical system. Both of these limitations are overcome by utilizing our 'open' microscope design approaches, by using appropriate radiation shielding near critical components and by enhancing the microscope with a sample transport system: this moves cell irradiation vessels between irradiation and imaging stations (http://users.ox.ac.uk/~atdgroup/radiation_linac.shtml).…”