Thermoluminescence of new Al2O3-BeO ceramics after exposure to high radiation doses.

New Al2O3-BeO ceramics were synthesized from alumina nanopowder in BeO crucibles by high-temperature treatment in reducing conditions. It was found that the TL curve of these ceramics is characterized by a dosimetric peak at 520-530 K for a heating rate of 2 K/s. The integrated TL of the peak is not influenced by the heating rate of the samples, unlike that in anion-defective alumina and beryllia crystals. The presence of an energy distribution of the traps which cause dosimetric TL peak is verified by Tm-Tstop and initial rise methods. Linear dependence on dose of the intensity of TL peak at 520-530 K is observed in the 10-300 Gy gamma-dose range. The diversity of TL sensitivity of the ceramic samples synthesized in one cycle does not exceed 10%. The results obtained show that the newly synthesized Al2O3-BeO ceramics are promising materials for TL dosimetry of high doses of ionizing radiation.

Dosimetric response for crystalline and nanostructured aluminium oxide to a high-current pulse electron beam.

The main thermoluminescent (TL) and dosimetric properties of the detectors based on anion-defective crystalline and nanostructured aluminium oxide after exposure to a high-current pulse electron beam are studied. TL peaks associated with deep-trapping centres are registered. It is shown that the use of deep-trap TL at 200-600°Ð¡ allows registering absorbed doses up to 750 kGy for single-crystalline detectors and those up to 6 kGy for nanostructured ones. A wide range of the doses registered, high reproducibility of the TL signal and low fading contribute to a possibility of using single-crystalline and nanostructured aluminium oxide for the dosimetry of high-current pulse electron beams.

Deep-trap competition model for TL in alpha-Al2O3:C heating stage.

The present report deals with the experimental observations of the thermally stimulated migration of charge carriers from trapping centres responsible for the main thermoluminescence (TL) peak at 450 K to a deep trap and, also, the optically stimulated transport of carriers from the deep trap to the main trap, which gives rise to the phototransferred TL at 450 K, in anion-defective alpha-Al2O3 crystals. The obtained results provide an experimental proof to the adequacy of the assumptions made in the model of the mutual interaction of the main and deep traps in the crystals under study.

Thermoluminescent dosemeters based on TLD-500 detectors for control of neutron fields.

The results of a study dealing with detection of neutrons in thermoluminescent (TL) photon radiation detectors, type TLD-500, based on an anion-defective corundum have been reported. The detection method uses the transformation of neutron radiation into gamma radiation arising when neutrons are captured by cadmium nuclei. A comparative analysis of the data obtained with the TL detectors and results of radiometric measurements suggested applicability of this method. A sensor with an optimal embodiment providing a relatively high sensitivity has been developed.

Thermoluminescent and dosimetric properties of anion-defective alpha-Al2O3 single crystals with filled deep traps.

Some new experimental results illustrating the effect of deep traps on luminescent and dosimetric properties of anion-defective single crystals of alpha-Al2O3 have been described. It was found that deep traps had an electronic origin. They were filled thanks to the photoionisation of F-centres and their filling was accompanied by the conversion of F-->F+ centres. The experiments revealed an interactive interaction of deep trapping centres. A model taking into account the thermal ionisation of excited states of F-centres was proposed. This model describes the trap filling process and mechanisms of the radio-, photo- and thermoluminescence, TSC and TSEE of the crystals under study. The sensitivity of TLD-500 detectors based on anion-defective alpha-Al2O3 equalised when deep trapping centres were filled.

A mathematical model for calculation of 90Sr absorbed dose in dental tissues: elaboration and comparison to EPR measurements.

A mathematical model for calculation of the 90Sr absorbed doses in dental tissues is presented. The results of the Monte-Carlo calculations are compared to the data obtained by EPR measurements of dental tissues. Radiometric measurements of the 90Sr concentrations. TLD and EPR dosimetry investigations were performed in animal (dog) study. The importance of the irregular 90Sr distribution in the dentine for absorbed dose formation has been shown. The dominant dose formation factors (main source-tissues) were identified for the crown dentine and enamel. The model has shown agreement with experimental data which allows to determine further directions of the human tooth model development.

The development of sex differences in cardiovascular disease mortality: a historical perspective.

OBJECTIVES: Little is known about why males have higher cardiovascular disease (CVD) mortality rates than do females. An important factor that has hampered efforts in this regard is the lack of clarity about whether male excess mortality from CVD has existed throughout history. To answer this question, an investigation was conducted of trends in CVD mortality differences between the sexes from the time when data first became available until the present, including the full range of age groups. METHODS: Mortality statistics for CVD in England and Wales from 1861 through 1992 and in the United States from 1900 through 1991 were used. RESULTS: Three stages in the relationship between male and female CVD mortality were found: (1) An early stage of equal male and female mortality, (2) a stage of the appearance of sex differences in mortality, and (3) a stage with consistently present male excess mortality. CONCLUSION: Male excess mortality from CVD has not always been present in the historical record. Further research is needed to elucidate the causes of this excess mortality.

Methods development for epidemiologic investigations of the health effects of prolonged ozone exposure. Part III. An approach to retrospective estimation of lifetime ozone exposure using a questionnaire and ambient monitoring data (U.S. sites).

Methods are needed for retrospective estimation of long-term ozone exposures in epidemiologic studies. The overall objective of this study was to evaluate whether data from available U.S. ozone monitoring sites are useful for estimating lifetime ozone exposures of young adults (for example, college students). Several aspects of this question were evaluated. First, we applied and (compared several spatial interpolation methods to a set of long-term average ozone data from all U.S. monitoring sites in operation from 1981 through 1990. Interpolation methods included simple and weighted averages, linear regression, and, in an exploratory way, kriging. The comparison of methods was carried out for five different metrics of ozone concentration: the daily one-hour maximum (MAX1) and eight-hour maximum (MAX8), the average ozone concentrations between 10 a.m. and 6 p.m. (MID8) and between 10 a.m. and 10 p.m. (MID12), and the sum of all hourly ozone concentrations greater than or equal to 60 parts per billion (ppb) (SUM06). We also tested whether interpolations were improved by modeling the influence of covariates such as population density, elevation, and weather on ozone concentrations. We analyzed the reliability of a set of newly developed questions about past activity levels among a group of 52 freshmen students at Yale University. This was done by analyzing the agreement between answers to the same questionnaire administered two times, one month apart (test and retest), to the same students. Finally, we combined the interpolation models with residential history information obtained by questionnaire to derive long-term ozone exposure estimates for a group of 200 Yale freshmen. Results of our study showed that the density of available monitoring sites appears to be adequate for estimating spatial patterns of long-term average ambient ozone concentrations. A simple regression-based interpolation on the three nearest sites produced consistently good results. Including covariates in the interpolation models did not substantially improve the estimates. The largest estimation errors occurred for areas where ozone concentrations were highest. The newly developed activity history questions exhibited fair to moderate reliability, The results of this work imply that reasonably precise estimates of long-term ambient ozone concentrations for use in large-scale epidemiologic studies can be achieved by interpolating ozone concentrations between available U.S. monitoring sites. This study did not address the issues of whether and how retrospective data on factors that modify exposure or dose (e.g., indoor/outdoor penetration of ozone and time outdoors) can be used to derive estimates of long-term personal ozone exposures and contribute to the assessment of received dose.

[Homology and evolution of gene orders: simulation and reconstruction of the evolutionary process]. / Gomologiia i évoliutsiia gennykh poriadkov: modelirovanie i rekonstruktsiia évoliutsionnogo protsessa.

A method to reconstruct the evolutionary history of observed gene orders from estimates of their similarity has been developed. It was shown that similarity measures accounting or not accounting for gene order in linkage groups of the compared genomes can be used for this purpose. A number of plausible variants of gene-order evolution from the common ancestral form in seven primate species were obtained.

[The clinico-epidemiological characteristics of natural-focus diseases in the Rukha garrison]. / Kliniko-épidemiologicheskaia kharakteristika prirodno-ochagovykh zabolevanii v garnizone Rukha.

The article gives the results of clinico-epidemiological studies of fever morbidity with unidentified etiology. The living quarter conditions of personnel in the Rukha locality contributed to the proliferation of mosquito fevers and mite-borne bilious typhoid among servicemen.