PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Lithium Compounds”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31Linked to original sources
PubMed2001

Isolation of reducing oligosaccharide chains from the chondroitin/dermatan sulfate-protein linkage region and preparation of analytical probes by fluorescent labeling with 2-aminobenzamide.

The glycosaminoglycan (GAG)-protein linkage regions of various proteoglycans share the common tetrasaccharide GlcA-Gal-Gal-Xyl-attached to Ser residues in the core proteins. In previous analysis we demonstrated unique modifications by epimerization, sulfation and phosphorylation of the component sugars. Here we developed a sensitive analytical method for the linkage region oligosaccharides to detect or monitor structural variations and changes. This will be useful for investigation of their biological roles, which are largely unknown, but they have been implicated in biosynthesis. A variety of linkage region-derived hexasaccharides was first prepared as reducing sugar chains from peptide chondroitin/dermatan sulfate of whale cartilage, shark cartilage, and bovine aorta by means of chondroitinase digestion in conjunction with beta-elimination in the absence of reducing reagents, but involving a mild alkali, 0.5 M LiOH, at 4 degrees C to prevent peeling reactions. The structures of these oligosaccharides were determined by the combination of HPLC, enzymatic digestion, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and (1)H NMR spectroscopy, which revealed eleven different hexasaccharides including a novel structure, DeltaHexAalpha1-3GalNAcbeta1-4IdoAalpha1-3Gal(4-O-sulfate)beta1-3Galbeta1-4Xyl (DeltaHexA and IdoA represent unsaturated hexuronic acid and L-iduronic acid, respectively). These oligosaccharides were labeled with a fluorophore, 2-aminobenzamide, to prepare analytical probes using the recently developed procedure [Kinoshita and Sugahara (1999) Anal. Biochem. 269, 367-378]. The fluorophore-tagged hexasacharides of low picomoles were well separated by HPLC and successfully analyzed by MALDI-TOF mass spectrometry. The principle of the method should be applicable to the analysis of the linkage region oligosaccharides derived from heparin and heparan sulfate as well.

Alkaline Phosphatase↗
PubMed2002

Low temperature studies in LiF:Mg,Cu,P.

Despite extensive investigations carried out in LiF:Mg,Cu,P, the nature of the emission centre is not clearly understood. Results of X ray excited emission in this material at room temperature and at 16 K are presented to obtain more data that can throw light on the emission characteristics of this material. At room temperature only a single emission peak is seen around 390 nm but at 16 K the emission appears to consist of more than one emission band. The emission spectra could be fitted with three bands with peaks at 332, 385 and 447 nm. The X ray excited emission at 16 K after annealing at 573 K for 5 min suppresses the 332 nm emission but enhances 447 nm emission. Moreover, annealing at 573 K greatly reduces the emission intensity, which signifies that the luminescent centres are also destroyed in this process. Temperature-dependent X ray excited fluorescence below room temperature provides evidence of the existence of shallow traps, which give rise to a thermoluminescence peak around 130 K. On the basis of the present investigations it is proposed that the complex nature of the emission may be related to the formation of donor-acceptor pairs in this material. The possible nature of this donor-acceptor complex is discussed.

Copper↗
PubMed2002

Microdosimetric interpretation of the photon energy response of LiF:Mg,Ti detectors.

Photon energy response of MTS-N (LiF:Mg,Ti) detectors (TLD Poland) and of MTS-N detectors sensitised with 200 Gy of 60Co gamma rays, followed by UV irradiation (sMTS-N), has been determined using X rays with narrow energy spectra, in the energy range from 20 to 300 keV. The over-response of LiF:Mg,Ti detectors for X rays (relative TL efficiency eta = 1.1) can be explained as an ionisation density effect. Low energy X rays produce short electron tracks, which locally deposit a high radiation dose and, consequently, lead to an enhanced (supralinear) response. This over-response has not been observed in sensitised MTS-N where supralinearity in the response after gamma ray doses above 1 Gy is not seen. Using the dose-response curves measured for MTS-N detectors after 137Cs gamma ray irradiation and local doses calculated using Monte Carlo generated electron tracks, it was possible to predict the relative TL effectiveness for different X ray energies. The calculation procedure can be applied to predict the photon energy response of LiF:Mg,Ti detectors in an arbitrary photon field.

Fluorides↗
PubMed2002

The composite structure of peak 5 in the glow curve of LiF:Mg,Ti (TLD-100): confirmation of peak 5a arising from a locally trapped electron-hole configuration.

The hypothesis that glow peak 5a arises from localised e-h capture is confirmed by the following experimental observations: (i) The high conversion efficiency (CE) (CE5a-->4 = 3 +/- 0.5) of peak 5a to peak 4 (a hole-only trap) deduced from detailed Im-Tstop optical bleaching studies at 310 nm compared to the much lower CE of peak 5 (an electron-only trap) (CE5-->4 = 0.0026+/-0.012). (ii) The lack of an increase in the sensitivity of glow peak 5a following 2.6 MeV and 6.8 MeV He ion irradiation in 'sensitised' material compared to the factor two increase in the sensitivity of peak 5; (S/S0)5a = 0.86+/-0.12, compared to (S/S0)5 = 2.0+/-0.2. (iii) The late entry into saturation of the 2.6 MeV and 6.8 MeV He ion TL-fluence response curves for peak 5a compared to peak 5 in sensitised and normal material resulting in the following values for the track radial saturation parameter: (r50)5a = 100+/-20) Angstroms compared to (r50)5 = 380+/-30 Angstroms. (iv) The low value of 0.1 for the 'track-escape' parameter of peak 5a deduced from the Extended Track Interaction Model analysis of He ion TL fluence response compared to order of magnitude greater values for peaks 5 and 5b.

Electrons↗
PubMed2002

Kinetic modelling of the optically stimulated conversion of peaks 5a and 5 to peak 4 in LiF:Mg,Ti (TLD-100).

The TC/LC conversion model for peaks 4, 5a and 5 in LiF:Mg,Ti (TLD-100) has been studied by solution of the coupled differential equations describing the charge carrier traffic following optical stimulation. Aspects of the model investigated were (i) the two-component exponential decay of the composite peak 5 TL intensity following the bleach, (ii) the role of retrapping during bleaching, (iii) the hole nature of peak 4 and (iv) the conversion of peak 5a traps to peak 4 traps. The high conversion efficiency is naturally explained due to the absence of conduction band competitive mechanisms in the optical ionisation of the electron in the e-h occupied structure corresponding to peak 5a and thereby leading to the hole-only occupied TC/LC leading to peak 4.

Fluorides↗
PubMed2002

Localised and delocalised optically induced conversion of composite glow peak 5 in LiF:Mg,Ti (TLD-100) to glow peak 4 as a function of postirradiation annealing temperature.

The composite structure of glow peak 5 in LiF:Mg,Ti (TLD-100) has been investigated using optical bleaching by 310 nm (4 eV) light. The glow peak conversion efficiency of peak 5a (Tm = 187 degrees C) to peak 4 traps is very high at a value of 3+/-0.5 (1 SD) whereas the glow peak conversion efficiency of peak 5 (Tm = 205 degrees C) to peak 4 traps is 0.0026+/-0.0012 (1 SD). The high conversion efficiency of peak 5a to peak 4 arises from direct optical ionisation of the electron in the electron-hole pair. leaving behind a singly-trapped hole (peak 4), a direct mechanism, relatively free of competitive mechanisms. Optical ionisation of the 'singly-trapped' electron (peak 5), however, can lead to peak 4 only via multi-stage mechanisms involving charge carrier transport in the valence and conduction bands, a mechanism subject to competitive processes. The conduction/valence band competitive processes lead to the factor of one thousand decrease in the conversion efficiency of peak 5 compared to peak 5a.

Fluorides↗
PubMed2002

Influence of fdelta(D) on modified track structure theory efficiency calculations.

Modified track structure theory (MTST) has been successfully applied to evaluate proton-to-gamma and helium-to-gamma relative TL efficiencies in LiF by using Monte Carlo radial dose distributions and the measured dose response function, fdelta(D), of 8.1 keV X rays. In this work, an investigation is performed to study the effect of the choice of fdelta(D) for the reference test radiation field, on the predicted MTST proton-to-gamma and helium-to-gamma efficiency values. Results from two sets of calculations are presented. Set 1 investigates five fdelta(D) functions with different shapes and its influence on the MTST efficiency values while set 2 applies MTST using several fdelta(D) functions selected with fdelta(D)max ranging from 2 to 4. Comparison of the predicted efficiency values with experimental data show that the choice of 8.1 keV X rays gives the best description of the data. Results from set 2 show that predicted efficiencies may vary by as much as 44% for peak 5 and as much as 70% for the total signal among different fdelta(D). This confirms the importance of using the adequate fdelta(D) from a test radiation which simulates as much as possible the energy spectra and irradiated volume produced by the secondary electrons arising from the heavy charged particle radiation under study.

Fluorides↗
PubMed2002

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.

Fluorides↗
PubMed2002

Thermoluminescent response of LiF:Mg,Ti to 20 keV electrons.

The thermoluminescence response of LiF:Mg,Ti (TLD-100) to 20 keV electrons from a scanning electron microscope has been measured. Radiochromic dye films previously calibrated were used to determine the fluence incident on TLD-100 chips. The procedure for irradiation and glow curve deconvolution was adhered to the protocols previously determined in our laboratory for gamma rays and heavy charged particles. The response at electron fluences higher than 4 x 10(10) cm(-2) is supralinear, due to the increasingly relevant contribution of the high temperature peaks. The relative contribution of the high temperature peaks to the TL signal is abnormally small, about half that observed in gamma irradiation and four times smaller than what has been measured in low-energy X ray exposure.

Electrons↗
PubMed2002

New evidence for spatially correlated TC-LC mechanisms in thermoluminescence of LiF:Mg,Ti.

New experimental investigations, consistent with the spatial coupling/perturbation between the trapping centres (TC) and luminescent centres (LC) giving rise to the peaks 5 and 4 thermoluminescence (TL) of LiF:Mg,Ti are discussed: (1) The glow peak widths of peaks 2 and 3 are constant as a function of Ti concentration, while the width of peak 4 decreases with a correlated increase in the width of peak 5. The dependence of glow peak shape on Ti concentration indicates that peaks 4 and 5 arise from a TC/LC spatially correlated extended defect. (2) The increased TL intensity of peak 5a following high ionisation density HCP irradiation compared to low ionisation density gamma irradiation strongly suggests that peak 5a arises from the geminate recombination of a locally trapped e-h pair. (3) The observation that the optical bleaching conversion efficiency (CE) of peak 5a to peak 4 is measured to be 3+/-0.5 and is three orders of magnitude greater than the CE of peak 5 to peak 4, is strong evidence for the unique structure of peak 5a--trap, i.e. peak 5a is due to a TC/LC structure which has captured an e-h pair, optical ionisation of the electron leads directly to the peak 4 TC.

Crystallization↗
PubMed2002

Lithium fluoride: from LiF:Mg,Ti to LiF:Mg,Cu,P.

Differences and similarities between LiF-based LiF:Mg,Ti and LiF:Mg,Cu,P are discussed, with respect to their dosimetric properties--sensitivity, non-linearity of dose response and heavy charged particle efficiency, as related to the concentration and the individual role of the Mg, Ti, Cu and P dopants. To study further the role of these dopants, the properties of some new, 'hybrid' phosphors: LiF:Mg,Cu,Ti and LiF:Mg,P, specially developed for this purpose, are also discussed. In the glow curve of LiF:Mg,Cu,P with a low concentration of Mg a new peak was found, which appears to be an analogue of peak 4 in LiF:Mg,Ti, Magnesium apparently controls most of the dosimetric properties of LiF-based phosphors. For instance, charged-particle efficiency appears to be anti-correlated with the concentration of Mg, being much less dependent on the content of other dopants. On the other hand, some properties of LiF-based systems seem to be correlated with changes in the emission spectra. It is suggested that Ti hampers the acceptance of any increased amount of Mg into more traps in LiF:MgTi. The absence of Ti, not the presence of P or Cu, is therefore a key to the high sensitivity of LiF:MgCuP.

Copper↗
PubMed2002

High resolution emission spectra of TL materials.

High resolution emission spectra of several TL materials, that are commonly used in dosimetry, were measured using a low cost fibre optic spectrometer containing a 2048 pixel CCD array. The spectra were taken from 177 to 890 nm with a wavelength resolution of 1.3 nm. This allowed for line width discrimination and the resolution of transitions that have not been seen so far. For rare earth doped materials like CaF2:Tm (TLD-300) and CaF2:Dy (TLD-200) the spectral lines were compared to the energy levels measured by Dieke and Crosswhite leading to the identification of most of the transition lines.

Aluminum Oxide↗
PubMed2002

A new high sensitivity thermoluminescent phosphor with low residual signal and good stability to heat treatment: LiF:Mg,Cu,Na,Si.

The preliminary investigations are reported on the characteristics of a new, high-sensitivity thermoluminescence phosphor material (LiF:Mg,Cu,Na,Si) prepared in this laboratory. The main dosimetric peak of this phosphor occurs at 197 degrees C at a heating rate of 1 degrees C.s(-1). The glow curve shape shows minimal differences and sensitivity remains stable when annealed in the range from 250 to 280 degrees C for 10 min. Its TL sensitivity to gamma radiation is about 30 times higher than that of TLD-100 with a residual signal 0.2% following a 260 degrees C readout at a heating rate of 15 degrees C.s(-1). This negligible residual signal renders LiF:Mg,Cu,Na,Si usable in unannealed form. Its TL response at both 260 degrees C and 280 degrees C are reproducible within a coefficient of variation of 2% over ten re-use cycles without systematic decrease. It retains the main advantages of LiF:Mg,Cu,P phosphor, and has a lower residual signal and a better stability to heat treatment.

Copper↗
PubMed2002

Role of impurities in the thermoluminescence of LiF:Mg,Cu,P.

The thermoluminescent properties of lithium fluoride doped with magnesium, copper and phosphorous are reviewed. This material shows specific advantages over LiF (TLD-100) in that is has higher sensitivity, less energy dependence and no supralinear behaviour with dose. However, it suffers from an irreversible loss in sensitivity when heated above 270 degrees C. Possible causes for this loss in sensitivity are discussed and experimental results are shown that indicate potential roles for the Cu, P and O impurities in this process. The present work focuses on the understanding of the impurity contents, inclusions, cluster formation and valence changes in this material by using differential scanning calorimetry (DSC) and glow discharge mass spectroscopy (GDMS). This research concludes that phosphorus inclusions are formed and a valence change of the Cu ions occurs after annealing above 270 degrees C, which degrades the TL sensitivity of LiF:Mg,Cu,P phosphors. It is also shown that a high content of oxygen in the material and control of the oxygen content during processing are critical to maintaining the sensitivity of these phosphors.

Calorimetry, Differential Scanning↗
PubMed2002

Thermoluminescence properties of LiMgF3 doped with Ce, Er and Dy.

The main dosimetric properties are reported of a new perovskite, LiMgF3, doped with Ce, Er and Dy impurities. An annealing temperature of 400 degrees C for one hour is necessary to erase any previous signal and to stabilise its sensitivity. A readout up to 450 degrees C gives the same result. The glow curve structure consists of two intense and isolated glow peaks at 170 degrees C and 315 degrees C. The sensitivity of both glow peaks to beta irradiation increases as the dopant concentration increases. The sensitivity is higher than that of LiF:Mg,Ti using the glow peaks 4+5 integral. Other properties like TL dose response, fading, sensitivity versus successive readout and ammealing cycles, sensitivity versus the heating rate, sensitivity to light and trapping parameter evaluation were also carried out.

Cerium↗
PubMed2002

Preparation, dosimetric characterisation and investigation of related TSL defect centres in Li3Po4:Mg,Cu phosphor.

L3PO4:Mg,Cu, a low effective atomic number and high sensitivity TSL phosphor, has been prepared. Its TSL glow curve shows a major peak around 360 degrees C with minor peaks around 110 degrees C and 230 degrees C. The optimum concentrations of the dopants are found to be 200 ppm each. Its gamma sensitivity is 1.2 times as compared to CaSO4:Dy (0.1 mol%). The optimum preirradiation annealing treatment is found to be 650 degrees C, 15 min. Its PL emission shows a band at 370 nm with excitation band at 250 nm. Dose to TSL response shows that its response is linear up to the gamma dose of 100 Gy for irradiations carried out at RT. An irradiated sample shows a distinct new ESR signal, which is tentatively assigned to an electron/hole localised on one of the oxygen(s) of the phosphate group. Step annealing experiments show decay of the defect centre around 340 degrees C. This correlates well with the TSL peak around 360 degrees C.

Copper↗
PubMed2002

Dosimetric characteristics of Li2B4O7:Cu,Ag,P solid TL detectors.

The main dosimetric characteristics are presented of newly prepared tissue-equivalent, highly sensitive thermoluminescent detector, Li,B4O7:Cu,Ag,P in the form of sintered pellets, developed at the Institute of Nuclear Sciences, Vinca. As a result of an advancement in the preparation procedure by the sensitising of basic copper activated lithium borate TL material, significant improvement in the TL sensitivity of Li2B4O7:Cu,Ag,P was gained. The glow curve of Li,B4O7:Cu,Ag,P consists of well defined main dosimetric peak situated at about 185-190 degrees C with the TL sensitivity which is about four to five times higher than that of LiF:Mg,Ti (TLD-100). From the experimental results a very wide linear dose response range, up to 10(3) Gy is evident. Dosimetric characteristics make sintered solid Li,B4O7:Cu,Ag,P TL detectors very promising for different dosimetry applications particularly in medical dosimetry and also for individual monitoring.

Borates↗