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[en] It is generally assumed that after the readout of TLD chips, all the traps are almost completely emptied and the residual readout is negligible. However, when performing routine readings (short readout times and high heating rates with no annealing), the deep traps are not completely cleared, and therefore, an additional readout of the crystal will indicate a residual dose. The residual dose for a normal additional readout (without any special treatment to enhance the residual dose, like UV irradiation) is about 0.2% of the accumulated historical dose of the TLD chip and could affect the result of the following readouts, especially when estimating low level doses
[en] The most widely used technique in radiation dosimetry is thermoluminescence (TL), which makes use of materials, commonly divided into two groups: (a) tissue equivalent phosphors, winch generally exhibit low sensitivity to ionizing radiation, e.g. Li:Mg, Ti , Li2B4O7 with Cu or Mn as impurities or Be203 with different impurities. (b) phosphors with high sensitivity but poor equivalence to organic tissue, e.g. CaF2 With Mn, Dy or Tm as impurities or CaSO4 with Mn or Tm as impurities. For a TL dosimeter used in personnel or environmental dosimetry, both tissue-equivalence and high sensitivity are required. Lithium fluoride doped with magnesium and titanium, known commercially as TLD-100 (Harshaw), is still the most commonly used radiation dosimeter. It has become popular because of several properties, such as tissue equivalence, relative low fading, adequate sensitivity for personnel dosimetry and the possibility to manufacture the material with acceptable reproducibility. The LiF:Cu, Mg, P phosphor has several important advantages compared to Li:Mg, Ti. The extended range of linearity, lack of supra linearity and the more nearly ideal tissue equivalence response to low energy photons gives a significant advantage in clinical dosimetry. The higher sensitivity, improved signal to noise ratio, and shorter monitoring periods lead to greatly improved performance in environmental dosimetry. The ultra low relative TL response to neutrons is another important advantage in mixed field neutron/gamma dosimetry. The Li:Mg, Cu, P does suffer from several of the disadvantages associated with TLD-100, especially its complex glow curve, and its greater sensitivity than TLD-100 to heating procedures. A comparison of some main properties of the two phosphors is presented in this work
[en] A brief editorial discusses the lack of consistency in the measured dosimetric characteristics of the thermoluminescent dosemeter material Lif:MgTi. It is suggested that this is due to various unplanned impurities and far greater efforts at quality control must be invested by the commercial industries supplying the materials. (UK)
[en] The present work reports on the evaluation of laser induced fluorescence (LIF) for the discrimination between different microbial strains. Pseudomonas aeruginosa and Staphylococcus aureus are important pathogenic bacteria for which therapeutic options are lacking nowadays. These microbial strains were selected due to their medical relevance as they are commonly found in human diseases infections. LIF is a spectrochemical analytical technique that was used in the present study to obtain bacteria spectral fingerprints in the liquid phase. Two laser wavelengths, 266 nm (UV) and 405 nm (violet), have been used as excitation light sources delivering output power 5 mW and 100 mW, respectively. The results of LIF analysis showed that the differences in fluorescence bands intensity can be used as a fingerprint for each bacterial species. In addition, the fluorescence emission intensities of the two strains were exponentially related to the concentration of the bacteria. Confocal laser scanning microscopy was used successfully to visualize the fluorescence emission of the cells in comparison with the LIF measurements. The obtained results demonstrate the potential of LIF as a fast, noninvasive, and easy technique for bacterial discrimination. The technique can be also used for the determination of bacteria concentration after performing proper calibration.
[en] The Moessbauer emission spectra of 57Co in low concentrations in KF, NaCl, NaF, LiF, and MgF2, and the effects of doping NaF and LiF with La3+ ions are reported. The monovalent halides all give similar spectra showing a broad single line or a doublet at 2.19 mm/s and two overlapping doublets at 0.46 and 0.19 mm/s (w.r.t metallic iron), although relative intensities vary. Previous Moessbauer and EPR spectroscopic data on these systems are reviewed briefly, and qualitative conclusions drawn on the chemistry of such systems. (author)
[en] Highlights: • Synthesis of undoped and Mg-doped LiF Phosphor. • Radiophotoluminescence (RPL) from F2 and F3+ centres. • Dose-response, fading and thermoluminescence (TL)-RPL correlation. • RPL and TL from undoped LiF recommended for high dose (1–15 kGy) dosimetry. • Yellow RPL emission through a 550 nm cut on filter can quickly confirm irradiation. Radiophotoluminescence (RPL) and thermoluminescence (TL) from undoped and Mg-doped LiF powder samples were investigated for high dose dosimetric applications. F-aggregate centres in LiF are created by radiolysis. The RPL emission at 530 nm and 650 nm from F3+ and F2 centres respectively (on excitation at 450 nm) in undoped commercial LiF powder enhanced with increasing sintering temperature. Its TL glow curve showed peaks at 145, 290 and 365 °C. The RPL-TL correlation studies carried out for the first time showed that the thermal annihilation of F3+ and F2 centes following Fi0 - Va (interstitial-vacancy) recombination cause 290 °C and 365° TL peaks respectively. This showed that F2 centres are thermally more stable than F3+ centres. Its integrated TL response kept increasing nearly linearly up to 14 kGy, in contrast to the response of the TL peaks in dosimetry grade LiF:Mg, Ti (TLD-100). However, the TL from LiF suffers from fading problems. A 100 °C, 15 min pre-read annealing treatment erased most of the 145 °C TL peak without disturbing the other high temperature peaks. A 750° C, 22 h sintering treatment in carbon atmosphere shifted the major TL glow peak of undoped LiF to 200 °C but reduced its TL sensitivity by more than a factor of 10. Mg-doped LiF samples exhibit a TL glow curve peaking at ∼240 °C with satellite peaks typical of Mg doped LiF whose shape did not change significantly with gamma dose. However it showed lower TL and RPL sensitivities as compared to those of undoped LiF. All LiF except LiF alfa (750 °C, 1 h, CB) showed sublinear increase in TL with dose and therefore will cause inaccuracy in dose measurements especially at high doses due to reduced sensitivity. LiF alfa 750 °C, 22 h and 1000 °C, 6 min sintered powder samples are better than others because their RPL sensitivity increases nearly linearly with dose. However, a low fading observed in the latter sample supports its application. The bright yellow RPL emission seen through a 550 nm cut on filter illuminated with a 450 nm blue LED or He-Cd laser light could quickly confirm an irradiated consignment on which LiF samples are affixed. The increase in green to red emission ratio with dose and post-irradiation storage period might be related to slow migration of anion vacancies created by one secondary electron track to F centres created by another track and consequent conversion of F2 → F3+ centres.