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At least 667 records · Page 37Linked to original sources
PubMed1982

Construction of a composite thin-element TLD using an optical-heating method.

A composite thermoluminescent dosimeter (TLD), composed of four, thin TL elements with a high-speed reader, has been developed by employing an optical-heating method. Each TL element, which is 15 mg/cm2 thick with a 3 mm dia., is prepared by applying Li2B4O7:Cu or CaSO4:Tm to a plastic substrate 14 mg/cm2 thick. Each element can be heated to 350 degree C within 0.8 sec. by IR radiation from a tungsten lamp. The characteristics of this TLD system include the following: (1) the detection limit of the Li2B4O7:Cu is 3 mR and the limit for CaSO4:Tm is 0.1 mR; (2) the energy-dependence curves are similar to the dose-equivalent curve, showing slight under-responses by 15% near 70 KeV for Li2B4O7:Cu and over-responses by 50% at high energies for CaSO4:Tm; (3) despite quick heating, the residual dose is as low as 0.1% of the last exposure signal; (4) responses are very stable for more than 1,000 cycles of repeated exposure readings; (5) no false signal could be detected, even in the cases of sweat or soil contamination; (6) the thin Li2B4O7;Cu element can be used for skin dose monitoring; and (7) the processing time of the automatic reader for the composite dosimeter is 3 hr/500 dosimeters. This TLD system can be applied to personnel dosimetry, gate monitoring and environmental monitoring.

Borates↗
PubMed1984

An improved volumetric dosimeter for internal dose verification.

The need for a volumetric dosimetry system for use in experiments to verify internal dosimetry calculations has been stressed previously. Such a system, consisting of a mixture of paraffin, tetrachlorobenzene and LiF TLD-100, has been developed at our institute. The dosimeter is essentially tissue equivalent and may be molded easily into any shape. Fabrication procedures and dosimeter-response characteristics of the system are presented. Results indicate no influence of the organic materials on the response of the TLD-100.

Chlorobenzenes↗
PubMed1984

A high sensitivity LiF thermoluminescent dosimeter--LiF(Mg, Cu, P).

This paper describes the dosimetric properties of a new, high-sensitivity thermoluminescence dosimeter material prepared in our laboratory. The sensitivity of the LiF(Mg, Cu, P) phosphor is about 23 times higher than that of LiF (TLD-100). Its TL response is linear from 0.3 mR to 1000 R. Its energy dependence is similar to that of LiF (TLD-100). It is stable and reusable without significant loss of sensitivity. Its application to environmental radiation monitoring is described.

Copper↗
PubMed1985

Using radiation damage to obtain a large quantity of matched-sensitivity thermoluminescent dosimeters.

We used radiation damage to reduce the sensitivity of thermoluminescent dosimeters (TLD) to match that of the working stock in our Dosimetry Laboratory. The mean sensitivity of the TLDs we altered fell within 1% of the stock mean and the distribution we obtained was much narrower than the +/- 10% limits on the working stock. By rejecting 1.5% of the test material, limits of +/- 5% could be established, thereby improving the precision of dosimetry measurements. The shapes of glow curves after irradiation remained unchanged. Our phototransferred thermoluminescence dose-reestimation procedure was still viable; however, the necessity for removing the TLDs' prior dose history became apparent, and we describe a procedure to handle this problem.

Fluorides↗
PubMed1985

A proposed modification of the cavity theory for electrons.

An empirical expression of cavity theory for electron fields is developed in a fashion similar to Burlin's general theory of cavity ionization for photons. It incorporates a term that relates the absorbed dose ratio in the cavity and material medium to the differences in electron scattering. This new expression correlates very well with experimental observations for progressively increasing LiF cavity sizes embedded in different media, the energy response of LiF at high electron energies relative to 60Co and the absorbed dose conversion factors CE in the ionization chamber dosimetry of electron beams.

Electrons↗
PubMed1986

Thermoluminescence response of LiF to alpha radiation.

The relative alpha-to-gamma radiation sensitivity of LiF chips (TLD-100) was determined using 241Am and 137Cs. Sensitivity is expressed in thermoluminescence per unit of absorbed dose in grays. The relative sensitivity varied from 0.13 to 0.23 with a mean of 0.18 +/- 0.03. The chips were exposed at ambient temperature and pressure.

Alpha Particles↗
PubMed1987

Experimental and computational techniques for beta-particle dosimetry.

This paper reports the experimental and the computational techniques that were specifically developed to provide dose response data for a new method of beta dosimetry, which is reported in an accompanying article (Sh87). The specific experimental techniques consist of setting up, calibrating and obtaining backscattering and resolution corrections for a plastic-scintillator-based beta spectrometer. The computation techniques involve (1) adapting a Monte Carlo electron transport computer code to use measured beta energy distributions as input data and (2) using the code to calculate the energy deposition of these distributions of electrons in a slab of material. The energy deposition of backscattered electrons incident on the slab is also taken into account. Codes, which were developed to calculate the energy deposited by photons in LiF, are used to derive a theoretical value for the TLD response calibration factor. This factor compares well to the experimentally derived result which was obtained by exposing TLDs to a calibrated 137Cs/137mBa photon source.

Algorithms↗
PubMed1987

An optimized computational method for determining the beta dose distribution using a multiple-element thermoluminescent dosimeter system.

This paper describes an optimization method for determining the beta dose distribution in tissue, and it describes the associated testing and verification. The method uses electron transport theory and optimization techniques to analyze the responses of a three-element thermoluminescent dosimeter (TLD) system. Specifically, the method determines the effective beta energy distribution incident on the dosimeter system, and thus the system performs as a beta spectrometer. Electron transport theory provides the mathematical model for performing the optimization calculation. In this calculation, parameters are determined that produce calculated doses for each of the chip/absorber components in the three-element TLD system. The resulting optimized parameters describe an effective incident beta distribution. This method can be used to determine the beta dose specifically at 7 mg X cm-2 or at any depth of interest. The doses at 7 mg X cm-2 in tissue determined by this method are compared to those experimentally determined using an extrapolation chamber. For a great variety of pure beta sources having different incident beta energy distributions, good agreement is found. The results are also compared to those produced by a commonly used empirical algorithm. Although the optimization method produces somewhat better results, the advantage of the optimization method is that its performance is not sensitive to the specific method of calibration.

Algorithms↗
PubMed1994

Monte Carlo calculations of monoenergetic electron depth dose distributions in LiF chips: skin dose correction factors for beta rays.

Monte Carlo calculations have been carried out for monoenergetic electrons from 0.1 to 4 MeV irradiating LiF chips in both perpendicular and isotropic geometry. This enabled the calculation of skin dose correction factors (beta factors) for typical beta energy spectra as measured with a beta-ray spectrometer at CANDU nuclear generating stations. The correction factors were estimated by averaging the depth dose distributions for the monoenergetic electrons over the experimentally measured beta-ray spectra. The calculations illustrate the large uncertainty in beta factors arising from the unknown angular distribution of the beta-ray radiation field and uncertainties in the shape of the beta-ray spectra below 500 keV.

Fluorides↗
PubMed1996

CaSO4:Dy and LiF:Mg, Cu, P thermoluminescent dosimeters for environmental monitoring in ambient areas of a nuclear power plant.

This paper describes CaSO4:Dy and LiF:Mg, Cu, P which were used for ambient environmental monitoring before the nuclear power plant operation in Guangdong Daya Bay, China, in 1991. Since LiF:Mg, Cu, P was first used as an environmental dosimeter in this laboratory, the intercomparison of both thermoluminescent dosimeters, including laboratory irradiation and environmental exposure in Beijing reference spots, was conducted in cooperation with National Institute of Metrology and Laboratory of Industrial Hygiene, measured values of both thermoluminescent dosimeters were in agreement with the error being less than +or- 2% for the laboratory irradiation. The results of measurement by both thermoluminescent dosimeters were quite in agreement with environmental reference exposure rates measured by a pressurized ionization chamber. The largest error of CaSO4:Dy environmental monitoring results in Daya Bay also showed that the differences of measurement results between two thermoluminescent dosimeters were not significant. The experiment results indicated that LiF:Mg, Cu, P was a good environmental dosimeter.

Calcium Sulfate↗
PubMed2003

Optimizing the use of LiF:Mg,Cu,P (GR-200 P) to measure low dose irradiation in nuclear medicine.

We undertook a study in order to determine the optimal conditions under which thermoluminescent powder LiF:Mg,Cu,P (GR-200 P) could be used for applications in nuclear medicine and for dosimetric needs. First, we defined the conditions chiefly related to the readout chain, namely the optimal mass of GR-200 material used for each readout, which is between 15 and 30 mg, and the optimal glow curve readout, which corresponds to heating in two phases: a rise in temperature at the rate of 10 degrees C s(-1) up to 150 degrees C followed by a plateau lasting 10 s and then another rise in temperature at the rate of 25 degrees C s(-1) up to 260 degrees C followed by a second plateau lasting 6 s. The optimum conditions for using TL material were also studied: using GR-200 P without annealing and performing two successive readouts of the same sample only led to a 0.1% loss in sensitivity per re-use cycle, and the good reproducibility of measurements was preserved with stable and weak residual TL signal. The response of the sample irradiated at three different dose levels with a 60Co gamma photon beam remained constant over 40 d. Sensitivity was preserved to within +/-4% between a few tenths of a microGy and 1 Gy. Our observations concur with the results of the literature and show how to optimize the conditions for using the GR-200 thermoluminescent dosimeter to measure low doses with a simple procedure that preserves the sensitivity of material.

Copper↗
PubMed2003

Risperidone in acute and continuation treatment of mania.

In a prospective study, we examined the efficacy of risperidone added-on to mood stabilizers in the acute and continuation treatment of mania over a 12-week period. Patients (n=108) with a DSM-IV diagnosis of bipolar disorder, manic or mixed episode requiring treatment with an antipsychotic were recruited. All subjects were on one or two mood stabilizers at the time of initiation of risperidone (range 0.5-4 mg). No other antipsychotic medication or ongoing benzodiazepine therapy was allowed. There was a significant decrease in mean Young Mania Rating Scale (YMRS) scores from baseline (27.5+/-7.5) to week 1 (-10.8, P<0.0001), week 3 (-17.7, P<0.0001) and to week 12(-22.6, P<0.0001). When response was defined as > or = 50% reduction in YMRS scores from baseline, 32%, 68% and 90% of patients met criteria at week 1, week 3 and week 12, respectively. Significant decreases in mean 21-item Hamilton Depression Rating Scale scores from baseline (12.2+/-7.7) to week 3 (-5.7, P<0.0001) and week 12 (-5.7, P<0.0001) were also observed. No significant changes in extrapyramidal symptoms were noted between baseline and endpoint. The mean daily dose of risperidone was 2 mg with a median of 1.8 mg. These findings support the results of the two previous double-blind, randomized trials and indicate that the addition of risperidone to mood stabilizers is a safe and effective treatment for acute and continuation treatment of mania. Risperidone add-on does not induce depressive symptoms and, furthermore, risperidone may have efficacy in treating comorbid depressive symptoms in bipolar patients.

Adult↗
PubMed2004

Risperidone plus lithium versus risperidone plus valproate in acute and continuation treatment of mania.

This exploratory analysis was performed to compare the efficacy and tolerability of risperidone when added to two different mood stabilizers (lithium or valproate) for mania in bipolar disorder. Patients receiving lithium or valproate at baseline were drawn from the database of a 12-week, open-label risperidone study. The primary efficacy measure was the Young Mania Rating Scale (YMRS). Other assessments included the Hamilton Rating Scale for Depression (HAM-D), Clinical Global Impression (CGI) of improvement, and safety measures. The analysis included 33 patients on lithium plus risperidone and 46 patients on valproate plus risperidone. Both subgroups had comparable baseline YMRS scores (lithium 28.2, valproate 28.7) and both had significant reductions in score by week 1 (P<0.0001). Comparable reductions in score continued for both subgroups until the end of the study (YMRS scores at week 12: lithium 4.6 and valproate 6.7). There were no significant differences in response rates (> or =50% improvement on YMRS) or remission rates (YMRS score < or = 8) between the two subgroups. At week 12, 88% of the lithium plus risperidone patients and 80% of the valproate plus risperidone patients were in remission. Similarly, HAM-D scores were significantly and comparably reduced in both subgroups, and improvement in CGI was the same. There was no difference between subgroups in the incidence of adverse events or weight gain. These data suggest that risperidone can be safely combined with either lithium or valproate, and that the efficacy is similar regardless of the mood stabilizer used.

Adolescent↗
PubMed2004

A review of acute treatments for bipolar depression.

Bipolar patients generally spend much more time in the depressed phase of their illness than the manic phase, and there are many more bipolar type II and bipolar spectrum disorder patients than there are bipolar type I. Additionally, there is a significant risk of suicide in bipolar patients when depressed. The treatment of the depressed phase of bipolar disorder is therefore a matter of some priority. Here, we review current evidence supporting the use of five groups of treatments: anti-depressants; lithium; anti-convulsants (valproate, and carbamazepine, lamotrigine, gabapentin); anti-psychotics; and other treatments (electroconvulsive therapy, benzodiazepines, sleep-deprivation, and dopamine agonists). From this review, it is apparent that the literature regarding the treatment of bipolar depression is significantly limited in several key areas. Nonetheless, from the evidence currently available, the treatments with the best evidence for efficacy are selective serotonin reuptake inhibitors (SSRIs) and lamotrigine. There is also some evidence in favour of bupropion and moclobemide. Although lithium and olanzapine monotherapies can also be beneficial, they appear less efficacious than antidepressants. One of the major concerns about treatment with antidepressants has been the risk of precipitating a switch into mania. However, recent studies suggest that, if a mood stabilizer and antidepressant are given concurrently, then the risk of switching is minimized. There is also recent evidence for an independent antidepressant action for at least one atypical antipsychotic. Therefore, the conclusion from this review, in contrast to previous suggestions, is that a combination of an atypical antipsychotic and either an SSRI or lamotrigine may provide a useful first-line treatment for depressed bipolar disorder patients. Further research is clearly required to examine this approach and compare it with other possible treatment options.

Anticonvulsants↗
PubMed1997

Bipolar illness.

BACKGROUND: Within the past 5 years, several factors have altered our view of the diagnosis, prognosis, treatment, and genetics of bipolar illness. METHODS: Significant advances in these areas are reviewed. RESULTS: Diagnostic changes include establishment of symptom duration requirements that limit confusion with affective instability. Prognostic insights include the realization that illness likely begets illness and, conversely, that adequate control is probably instrumental in improving long-term prognosis. Therapeutic advances are marked by the Food and Drug Administration approval of divalproex for acute mania. CONCLUSIONS: Genetic and family studies suggest that (1) bipolar illness is a discrete condition, not related to unipolar depression; and (2) bipolar illness may manifest a phenomenon known as anticipation (worsening of the disease with succession generations), which may be related to a specific nucleic acid abnormality.

Bipolar Disorder↗
PubMed2006

Lithium improves HIV-associated neurocognitive impairment.

OBJECTIVE: To determine the effects of low-dose oral lithium on the neuropsychological performance of individuals diagnosed with HIV-associated neurocognitive impairment. DESIGN AND METHODS: The project was a single-arm, open-label, 12-week pilot study at a university-based tertiary care center. The participants were adults who had been diagnosed with HIV-associated neurocognitive impairment and had been on stable antiretroviral therapy for at least 12 weeks. Conditions that could affect cognition, worsen adherence to study procedures, or increase the risk of lithium adverse reactions were excluded. Twenty-one individuals were screened and eight were enrolled, all of whom completed the study. Oral lithium was initiated at 300 mg daily and was titrated to maintain 12-h trough concentrations between 0.4 and 0.8 mEq/l. Global neuropsychological performance was assessed by the global deficit score. RESULTS: At baseline, all participants had impaired neuropsychological performance and most had reduced CD4 cell counts (median 292 cells/microl), and HIV RNA levels in plasma below 400 copies/mL (seven of eight). Titrated lithium doses ranged between 600 and 1200 mg/day. Performance improved in all eight individuals after 12 weeks, and became unimpaired in six. The study treatment was well tolerated with no grade 3 or 4 adverse events and no premature discontinuations. CONCLUSIONS: Lithium resulted in improved neuropsychological performance in antiretroviral-treated, impaired individuals in this small, open-label study. Based on published in vitro data, lithium may exert this effect by inhibiting neuronal glycogen synthase kinase-3beta.

Administration, Oral↗