Dose dependences of radiation induced yield in mixed radiation fields.

A theoretical model that describes dose dependences of trap filling (radiation yield) in mixed radiation fields consisting of two components is proposed. The model consists of one type of electron traps and one type of hole traps and assumes as an initial step the creation of two types of tracks, each represented by some volume with a uniform electron-hole pair density, different for each track. The relaxation process that follows comprises interband recombination, trapping of electrons and holes, and recombination of electrons with trapped holes and of holes with trapped electrons. These processes result in filled traps in amounts depending on the absorbed dose in the track and the number and types of tracks created in a given region of irradiated matter. The summation over the matter with areas of different degrees of overlapping (assuming poisson distribution of the created tracks), gives expressions for the dependences of trap filling as a function of doses for separated and simultaneous irradiation. It is shown that the key parameters determining the behaviour of the dose dependences are the ratios between the doses in the separated tracks and the average doses delivered on the irradiated matter by the separated components of the mixed field. If the ratios of the average dose to the track dose are low, the dose dependences will be linear. In the opposite limiting case the dose dependencies go to saturation. The linear and additive approximations of dose dependences in a mixed field are valid at low doses only.

Optical absorption, TL and IRSL of basic plagioclase megacrysts from the pinacate (Sonora, Mexico) quaternary alkalic volcanics.

The paper presents the first results of an investigation on optical absorption (OA), thermally and infrared stimulated luminescence (TL and IRSL) of the Pinacate plagioclase (labradorite). The OA spectra reveal two bands with maxima at 1.0 and 3.2 eV connected with absorption of the Fe3+ and Fe2+ and IR absorption at wavelengths longer than 2700 nm. The ultraviolet absorption varies exponentially with the photon energy following the 'vitreous' empirical Urbach rule indicating exponential distribution of localised states in the forbidden band. The natural TL is peaked at 700 K. Laboratory beta irradiation creates a very broad TL peak with maximum at 430 K. The change of the 430 K TL peak shape under the thermal cleaning procedure and dark storage after irradiation reveals a monotonous increasing of the activation energy that can be explained by the exponential distribution of traps. The IRSL response is weak and exhibits a typical decay behaviour.

Participation of Eu-aggregates in the photoluminescence, afterglow and thermoluminescence of UV-irradiated KCl:Eu at 20 K.

The participation of different aggregated phases of the Eu impurity in the afterglow (AG) and thermoluminescence (TL) of KCl:Eu after UV-irradiation at 20 K is investigated. Several aggregated phases of Eu are formed by applying different thermal treatments and their formation is monitored by photoluminescence. It is shown that the treatments leading to high concentration of aggregates result in much higher AG and TL yields than the treatments leading to high concentration of dipoles. This is due to a more efficient AG and TL production for aggregates than for dipoles. Additionally, we observed a huge increase of the AG and TL production efficiency around dipoles after ageing at 200 °C. The results are discussed in view of a recently proposed mechanism for AG based on the migration of H centres through dislocation lines. The main conclusions are that dislocation lines trap dipoles and that precipitation occurs along dislocation lines causing a large fraction of aggregates to participate in the AG and TL.

Temperature variation of the shape of the F band in undoped LiF.

The optical absorption (OA) spectra between 3.1 and 6.2 eV of undoped X ray irradiated LiF measured during and after linear heating up to increasing end temperatures have been studied. The temperature variation of the OA near 5 eV, which is usually attributed to F centres has been analysed by direct comparison between different OA spectra and by deconvolution of the OA spectra. It was found that the OA consists of three overlapping bands belonging to three different centres. The bands. which are Gaussian with maxima at 4.4, 4.78 and 5.08 eV (at 300 K), have different behaviour under thermal treatment. The most stable band is the 5.08 eV band, which corresponds to the pure F centres. The 4.78 eV band disappears completely after heating up to 600 K and was supposed to be connected with F1 centres. The 4.4 eV band (absent after irradiation) starts to incrcase and decrease after passing a maximum with temperature increasing. The 4.78 and 5.08 eV bands show strong linear temperature dependencies of the maximum position and the width.

Thermoluminescence properties of KCl(1-X)KBrX:Pb2+ mixed crystals.

A study is presented of the thermoluminescence (TL) of phosphors based on potassium halides doped with divalent lead, such as KCl:Pb2+, KBr:Pb2+ and the crystalline series KCl(1-X)Br(X):Pb2+. The defects in the crystals generated by irradiation have been investigated as well as the trapping and room temperature recombination mechanisms. The samples were gamma irradiated to a dose of 10 kGy. The TL spectral response during the recombination stage was obtained through simultaneous measurements of temperature, emitted light intensity and emission wavelength by using an automated thermoluminescence system with optical fibre couplings and a diode array as a detection device. The TL emission is a broad band in the 350-600 nm range with a maximum strongly dependent upon the mixed composition.