Luminescence of X-ray induced radiation defects in modified lithium orthosilicate pebbles with additions of titanium dioxide

Modified lithium orthosilicate (Li4SiO4) pebbles with additions of titanium dioxide (TiO2) are designed as a possible tritium breeder ceramic for the helium cooled pebble bed (HCPB) test blanket module. Additions of TiO2 were chosen to enhance mechanical properties of the tritium breeder pebbles. The formation of radiation defects (RD) in the modified Li4SiO4 pebbles with a different content of TiO2 was studied by X-ray induced luminescence (XRL) technique. After XRL measurements the accumulated RD were also analyzed by thermally stimulated luminescence (TSL) and electron spin resonance (ESR) spectrometry. XRL spectra consist of several bands with maxima at around 430, 490, 690, 700 and 800 nm. The XRL band with a peak at 490 nm could be associated with intrinsic defects in Li4SiO4 matrix whereas all the other maxima at lower photon energies are the result of the addition of TiO2.

ESR spectroscopy of alanine impacted by high energy irradiations for wide range dosimetry

The ESR spectrometry, based on alanine dosimeters, is a standard tool for dosimetry of different type ionizing radiations. The calibrated dosimeters and ESR readers operate rather reliably in the dose range up to 200 kGy. In this study, the ESR spectrometry of stable free radicals in alanine, induced by penetrative X- and γ-rays as well as neutron and stopped proton irradiations covering the dose range from a few Gy to a few MGy, has been performed in order to create the generalized calibration function for the wide range dosimetry. The simulations based on the cumulative generation of ESR active stable radicals R1, R2 and R3 enabled us to derive the generalized calibration model ascribed to the irradiation fluence from 1010to 2 × 1016particle/cm2normalized using 1 MeV neutron equivalent.

Free radical formation in freeze-dried raw milk in relation to its α-tocopherol level

Lipid oxidation in milk and dairy products is a chain reaction initiated by formation of free radicals (Richardson & Korycka-Dahl, 1983). Thanks to intensive studies on both model systems and actual food, the autocatalytic process, including the formation of secondary lipid oxidation products from the lipid hydroperoxides formed initially, is fairly well understood. However, actually predicting the rate at which the first free radicals leading to spontaneous oxidation are formed in milk from different cows awaits the development of new analytical methods with higher specificity and sensitivity (Nicholson, 1993; Barrefors et al. 1995). Such methods would also be valuable for predicting the stability and shelf life of dried dairy products, which are determined by oxidative phenomena. Electron spin resonance (ESR) spectrometry has the potential for detecting the early events in lipid oxidation, as it is the only spectrometric method that will directly detect the unpaired electron characteristic of the free radical and it is, moreover, a highly sensitive method (Brudvig, 1995). ESR spectrometry has recently been shown to provide quantitative information on the level of free radicals in milk powder that correlates with the level of secondary oxidation products developed upon reconstitution and that also correlates with subsequent sensory evaluation (Nielsen et al. 1997; Stapelfeldt et al. 1997a, b, c). However, in order to explore further the potential of this method for raw milk, it was considered valuable to measure the tendency of milk to form free radicals in relation to its level of α-tocopherol, the most important lipophilic chain-breaking antioxidant (cf. Kamal-Eldin & Appelqvist, 1996).