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Results for “Lithium Compounds”

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At least 361 records · Page 20Linked to original sources

PubMed1990

Influence of resorbable poly(L-lactide) bone plates and screws on the dose distributions of radiotherapy beams.

Metallic bone plates have been shown to affect radiation in vitro. Although no damage has ever been demonstrated in vivo these plates may cause dose enhancements and shielding of the adjacent tissue. Resorbable high molecular weight as-polymerized poly(L-lactide) (PLLA) bone plates have recently been used for reconstruction in the maxillofacial area. To determine their influence on dose distribution, a 4-hole bone plate and screws of PLLA were exposed to electron and photon beams. A tissue-equivalent phantom of perspex was irradiated and measurements were made with LiF thermoluminescent dosimeters. No significant changes in dose deviations could be determined when the dose distribution in the homogeneous phantom was compared with that of the phantom in which the PLLA material was placed. From this study it can be concluded that the PLLA material can be regarded as tissue-equivalent and can, thus, be safely used for fracture fixation of bone fragments when postoperative irradiation is anticipated.

Bone Plates↗

PubMed2002

Lithium: poisonings and suicide prevention.

This study concerns 81 cases of lithium poisoning and shows that deliberate intoxications are prevalent during the first 3 years of lithium treatment as well as in cases with a previous history of suicide attempt. Therapeutic intoxications could generally be avoided by education concerning hygiene and diet and careful monitoring in cases of intercurrent diseases.

Adult↗

PubMed2002

TLD linearity vs. beam energy and modality.

Thermoluminescent dosimetry (TLD) is considered to be a valuable dosimetric tool in determining patient dose. Lithium fluoride doped with magnesium and titanium (TLD-100) is widely used, as it does not display widely divergent energy dependence. For many years, we have known that TLD-100 shows supralinearity to dose. In a radiotherapy clinic, there are multiple energies and modality beams. This work investigates whether individual linearity corrections must be used for each beam or whether a single correction can be applied to all beams. The response of TLD as a function of dose was measured from 25 cGy to 1000 cGy on both electrons and photons from 6 to 18 MeV. This work shows that, within our measurement uncertainty, TLD-100 exhibits supralinearity at all megavoltage energies and modalities.

Fluorides↗

PubMed2001

Investigation on molar mass, solubility and enzymatic fragmentation of xylans by multi-detected SEC chromatography.

Four xylan samples from different origin were investigated, using a multi-detector, size exclusion, chromatographic system with two chromatographic column sets and mobile phases differing in the DMSO:water ratio. Molar mass distribution could be analysed best using a mobile phase of DMSO:water (90:10) with addition of 0.05 M LiBr, a system offering good solubilisation of the polymers and a proper chromatographic separation. SEC analysis in aqueous systems provided information on solubility and aggregation of xylans. A comparison of UV- and RI-signals in different systems gave further information on lignin impurities, which in some cases were involved in aggregation phenomena. Both analytical systems were applied to study the enzymatic fragmentation of xylans. Combining the information derived from the two systems can differentiate between the enzymatic degradation of the well-dissolved and the associated polymer fractions.

Bromides↗

PubMed2002

Design and synthesis of 4,5-disubstituted-thiophene-2-amidines as potent urokinase inhibitors.

A study of the S1 binding of lead 5-methylthiothiophene amidine 3, an inhibitor of urokinase-type plasminogen activator, was undertaken by the introduction of a variety of substituents at the thiophene 5-position. The 5-alkyl substituted and unsubstituted thiophenes were prepared using organolithium chemistry. Heteroatom substituents were introduced at the 5-position using a novel displacement reaction of 5-methylsulfonylthiophenes and the corresponding oxygen or sulfur anions. Small alkyl group substitution at the 5-position provided inhibitors equipotent with but possessing improved solubility.

Alkylation↗

PubMed1994

Stereocontrolled synthesis of C-glycosides: further studies on the organolithium reagents derived from 2-deoxy-D-glucose and D-glucose.

The addition of alpha- and beta-2-deoxy-D-glucopyranosyl lithium reagents i and ii to prochiral aldehydes is a syn-selective process, synthetically useful only with the alpha-lithio reagent i (syn:anti selectivity of approximately 10:1 with saturated aldehydes). This has been demonstrated by using propionaldehyde and converting the syn-isomers of both series to an easily identified acyclic meso-chain (alpha-series) or a C2 symmetric acyclic chain (beta-series). The preparation of alpha- and beta-D-glucopyranosyl dilithio reagents 26 and 27 is possible but a notable decrease in efficiency and facial selectivity is observed in coupling reactions with model aldehydes.

Aldehydes↗

PubMed2003

Development of a low-energy monoenergetic neutron source for applications in low-dose radiobiological and radiochemical research.

The McMaster University 3 MV KN Van de Graff accelerator facility primarily dedicated to in vivo neutron activation measurements has been used to produce moderate dose rates of monoenergetic fast neutrons of energy ranging from 150 to 600 keV with a small energy spread of about 25 keV (1sigma width of Gaussian) by bombarding thin lithium targets with 2.00-2.40 MeV protons. The calculated dose rate of the monoenergetic neutrons produced using thin lithium targets as functions of beam energy, target thickness, lab angle relative to beam direction, and the solid angle subtended by the sample with the target has also been reported.

Equipment Design↗

PubMed2003

A personal thermoluminescence dosimeter using LiF:Mg,Cu,Na,Si detectors for photon fields.

A new personal thermoluminescence (TL) dosimeter for photon fields using LiF:Mg,Cu,Na,Si TL detector was developed by taking advantage of its dosimetric properties including energy dependencies. Solid pellet type LiF:Mg,Cu,Na,Si detector was developed and fabricated at Korea Atomic Energy Research Institute (KAERI) and has been studied on its dosimetric properties such as TL grow curve, dose response, energy response and reusability. Its dosimetric properties show the feasibility of application of LiF:Mg,Cu,Na,Si TL detector to personal dosimetry fields. A new dosimeter using LiF:Mg,Cu,Na,Si TL detector was designed and tested through irradiation experiments. This multi-element TL dosimeter allows the measurement of a personal dose equivalent Hp(d) in photon fields. Based on the experimental results of the proposed dosimeter, it was demonstrated that a personal TL dosimeter using sintered LiF:Mg,Cu,Na,Si TL detector is appropriate to estimate personal dose equivalent for wide range energy of photon fields.

Copper↗

PubMedDate not supplied

Dependence of TLD thermoluminescence yield on absorbed dose in a thermal neutron field.

The emission from 6LiF and 7LiF thermoluminescence dosimeters (TLDs) exposed to the mixed field of thermal neutrons and gamma-rays of the thermal facility of a TRIGA MARK II nuclear reactor has been investigated for various thermal neutron fluences of the order of magnitude of those utilised in radiotherapy, with the purpose of investigating the reliability of TLD readouts in such radiation fields and of giving some information for better obtainment of the absorbed dose values. The emission after exposure in this mixed field is compared with the emission after gamma-rays only. The glow curves have been deconvoluted into gaussian peaks, and the differences in the characteristics of the peaks observed for the two radiation fields, having different linear energy transfers, and for different doses are shown. Irreversible radiation damage in dosimeters having high sensitivity to thermal neutrons is also reported, showing a memory effect of the previous thermal neutron irradiation history which is not restored by anneal treatment.

Fluorides↗

PubMed1998

Use of Chinese LiF:Mg,Cu,P (GR-200) TL detectors at therapy-level absorbed doses.

The objective was to find out whether or not the highly radiation-sensitive Chinese thermoluminescent (TL) LiF:Mg,Cu,P (GR-200) detector pellets can be used in therapy-level dosimetry. For this purpose the precision was investigated at an absorbed dose level of 1 Gy using a commercial TL read-out instrument. Relative standard deviations, sigma rel, of the individual calibration factors were found to be in the range between 0.2% and 0.6% from 30 randomly selected detectors, with the mean at 0.37%. Apart, linearity checks between 1 and 6 Gy resulted into a sublinear response of up to -4% which was successfully corrected for by a third-order polynomial curve fit. The residual signal turned out to be about 0.1% after one annealing cycle almost independent of the applied dose, and this figure could be reduced by two more decades after repeated annealing cycles.

Copper↗

PubMed1998

Effects of dose reduction on the detectability of standardized radiolucent lesions in digital panoramic radiography.

Dose reduction in digital panoramic radiography was studied. Intentional underexposure was performed with the Orthophos DS while six different human mandibles were radiographed. Exposure settings were 69 kV/15 mA (standard), 64 kV/16 mA, and 60 kV/16 mA. Standardized spherical defects, each either 1 or 1.25 mm in diameter, were simulated in 288 of 432 images, and seven observers decided whether defects were present or not. Areas under the receiver operating characteristics curves were calculated. They showed no significant differences in the detectability of the 1-mm defect at 69, 64, or 60 kV. For the 1.25-mm defect, no difference was found between the 69 and 60 kV images, but a statistically significant different detectability was found for 64 kV images in comparison with both 69 and 60 kV images. A dose reduction of up to 43% was ascertained with a Pedo-RT-Humanoid phantom when panoramic radiography was performed at 60 kV/16 mA. The conclusion is that with the Orthophos DS, it seems possible to reduce the dose rate of x-rays without loss of diagnostic quality in the case of radiolucent changes.

Fluorides↗

PubMed2003

Improving W-band pulsed ENDOR sensitivity--random acquisition and pulsed special TRIPLE.

Two approaches for improving the signal-to-noise ratio (S/N) of W-band pulsed electron-nuclear double resonance (ENDOR) spectra are presented. One eliminates base-line problems while the other enhances the ENDOR effect. High field ENDOR spectra measured at low temperatures often suffer from highly distorted base-lines due to the heating effect of the RF pulses that causes some detuning of the cavity and therefore leads to a reduction in the echo intensity. This is a severe problem because it often masks broad and weak ENDOR signals. We show that it can be eliminated by recording the ENDOR spectrum in a random, rather than the standard sequential variation of the RF frequency. The S/N of the ENDOR spectrum can be significantly enhanced by the application of the pulse analog of the continuous wave (CW) special TRIPLE experiment. While this experiment is not applicable in the solid state at conventional X-band frequencies, at W-band it is most efficient. We demonstrate the efficiency of the special TRIPLE Davies and Mims experiments on single crystals and orientationally disordered systems.

Copper↗

PubMed1999

Strategies for treatment-resistant depression.

Clinical depression is a common disorder with serious implications that is often misdiagnosed or underestimated. More than 50% of suicides are associated with a major depressive disorder, and depression can adversely impact a variety of other medical conditions. Although > or = 70% of depressions can respond to appropriate medications, few patients actually receive adequate medical therapy. This article reviews the definition of adequate therapy for depression, discusses common comorbid conditions, and examines the issue of true treatment resistance. Practical strategies for treatment-resistant depression, including switching classes of antidepressant drugs, combination therapy, augmentation strategies, and somatic therapies, are incorporated into a treatment algorithm.

Antidepressive Agents↗

PubMed2001

Neutron dosimetric measurements in shuttle and MIR.

Detector packages consisting of thermoluminescence detectors (TLD), nuclear emulsions and plastic track detectors were exposed at identical positions inside MIR space station and on shuttle flights inside Spacelab and Spacehab during different phases of the solar cycle. The objectives of the investigations are to provide data on charge and energy spectra of heavy ions, and the contribution of events with low-energy deposit (protons, electrons, gamma, etc.) to the dose, as well as the contribution of secondaries, such as nuclear disintegration stars and neutrons. For neutron dosimetry 6LiF (TLD600) and 7LiF (TLD700) chips were used both of which have almost the same response to gamma rays but different response to neutrons. Neutrons in space are produced mainly in evaporation and knock-on processes with energies mainly of 1-10 MeV and up to several 100 MeV, respectively. The energy spectrum undergoes continuous changes toward greater depth in the attenuating material until an equilibrium is reached. In equilibrium, the spectrum is a wide continuum extending down to thermal energies to which the 6LiF is sensitive. Based on the difference of absorbed doses in the 6LiF and 7LiF chips, thermal neutron fluxes from 1 to 2.3 cm-2 s-1 are calculated using the assumption that the maximum induced dose in TLD600 for 1 neutron cm-2 is 1.6 x 10(-10) Gy (Horowitz and Freeman, Nucl. Instr. and Meth. 157 (1978) 393). It is assumed that the flux of high-energy neutrons is at least of that quantity. Tissue doses were calculated taking as a mean ambient absorbed dose per neutron 6 x10(-12) Gy cm2 (for a10 MeV neutron). The neutron equivalent doses for the above-mentioned fluxes are 52 micro Gy d-1 and 120 micro Gy d-1. In recent experiments, a personal neutron dosimeter was integrated into the dosimeter packages. First results of this dosimeter which is based on nuclear track detectors with converter foils are reported. For future measurements, a scintillator counter with anticoincidence logic is under development.

Cosmic Radiation↗

PubMed2001

Neutron dosimetry in low-earth orbit using passive detectors.

This paper summarizes neutron dosimetry measurements made by the USF Physics Research Laboratory aboard US and Russian LEO spacecraft over the past 20 years using two types of passive detector. Thermal/resonance neutron detectors exploiting the 6Li(n,T) alpha reaction were used to measure neutrons of energies <1 MeV. Fission foil neutron detectors were used to measure neutrons of energies above 1 MeV. While originally analysed in terms of dose equivalent using the NCRP-38 definition of quality factor, for the purposes of this paper the measured neutron data have been reanalyzed and are presented in terms of ambient dose equivalent. Dose equivalent rate for neutrons <1 MeV ranged from 0.80 microSv/d on the low altitude, low inclination STS-41B mission to 22.0 microSv/d measured in the Shuttle's cargo bay on the highly inclined STS-51F Spacelab-2 mission. In one particular instance a detector embedded within a large hydrogenous mass on STS-61 (in the ECT experiment) measured 34.6 microSv/d. Dose equivalent rate measurements of neutrons >1 MeV ranged from 4.5 microSv/d on the low altitude STS-3 mission to 172 microSv/d on the ~6 year LDEF mission. Thermal neutrons (<0.3 eV) were observed to make a negligible contribution to neutron dose equivalent in all cases. The major fraction of neutron dose equivalent was found to be from neutrons >1 MeV and, on LDEF, neutrons >1 MeV are responsible for over 98% of the total neutron dose equivalent. Estimates of the neutron contribution to the total dose equivalent are somewhat lower than model estimates, ranging from 5.7% at a location under low shielding on LDEF to 18.4% on the highly inclined (82.3 degrees) Biocosmos-2044 mission.

Fast Neutrons↗

PubMed1996

Neutron fluences and dose equivalents measured with passive detectors on LDEF.

Neutron fluences were measured on LDEF in the low energy (< 1 MeV) and high energy (> 1 MeV) ranges. The low energy detectors used the 6Li(n,alpha)T reaction with Gd foil absorbers to separate thermal (< 0.2 eV) and resonance (0.2 eV-1 MeV) neutron response. High energy detectors contained sets of fission foils (181Ta, 209Bi, 232Th, 238U) with different neutron energy thresholds. The measured neutron fluences together with predicted spectral shapes were used to estimate neutron dose equivalents. The detectors were located in the A0015 and P0006 experiments at the west and Earth sides of LDEF under shielding varying from 1 to 19 g/cm2. Dose equivalent rates varied from 0.8 to 3.3 microSv/d for the low energy neutrons and from 160 to 390 microSv/d for the high energy neutrons. This compares with TLD measured absorbed dose rates in the range of 1000-3000 microGy/d near these locations and demonstrates that high energy neutrons contribute a significant fraction of the total dose equivalent in LEO. Comparisons between measurements and calculations were made for high energy neutrons based on fission fragment tracks generated by fission foils at different shielding depths. A simple 1-D slab geometry was used in the calculations. Agreement between measurements and calculations depended on both shielding depth and threshold energy of the fission foils. Differences increased as both shielding and threshold energy increased. The modeled proton/neutron spectra appeared deficient at high energies. A 3-D model of the experiments is needed to help resolve the differences.

Extraterrestrial Environment↗

PubMed2000

TLD efficiency of 7LiF for doses deposited by high-LET particles.

The efficiency of 7 LiF TLDs (TLD-700) in registering dose from high-LET (> or = 10 keV/micrometers) charged particles (relative to 137Cs gamma rays) has been measured for a number of accelerated heavy ions at various particle accelerator facilities. These measured efficiency values have been compared with similar results obtained from the open literature and a dose efficiency function has been fitted to the combined data set. While it was found that the dose efficiency is not only a function of LET, but also of the charge of the incident particle, the fitted function can be used to correct the undermeasured value of dose from exposures made in mixed radiation fields where LET information is available. This LET-dependent dose efficiency function is used in our laboratory in determining total absorbed dose and dose equivalent from combined TLD and CR-39 plastic nuclear track detector measurements.

Calibration↗

PubMed2000

Vibrational spectroscopic studies on ion solvation of lithium perchlorate in propylene carbonate + N,N-dimethylformamide mixtures.

The infrared (IR) and Raman spectra are reported for solutions of lithium perchlorate in propylene carbonate (PC), N,N-dimethylformamide (DMF) and PC + DMF mixtures. The band splittings of symmetric ring deformation for PC and O=CN deformation for DMF suggest that there is a strong interaction between lithium cations and solvent molecules. The solvent molecules have been assigned to two types, the free and complexed molecules. By a comparison of the intensity for the corresponding bands, it has been concluded that Li+ cations are preferentially solvated by DMF molecules in the LiClO4/PC-DMF solutions. This has been explained by the difference in values of donor number.

Carbonates↗