Browsing by Subject "radiation"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Aerosol optical properties and their radiative effects in northern China(AGU, 2007-08-29) Li, Zhanqing; Xia, Xiangao; Cribb, Maureen; Mi, Wen; Holben, Brent; Wang, Pucai; Chen, Hongbin; Tsay, Si-Chee; Eck, Thomas; Zhao, Fengsheng; Dutton, E. G.; Dickerson, R. E.As a fast developing country covering a large territory, China is experiencing rapid environmental changes. High concentrations of aerosols with diverse properties are emitted in the region, providing a unique opportunity for understanding the impact of environmental changes on climate. Until very recently, few observational studies were conducted in the source regions. The East Asian Study of Tropospheric Aerosols: An International Regional Experiment (EAST-AIRE) attempts to characterize the physical, optical and chemical properties of the aerosols and their effects on climate over China. This study presents some preliminary results using continuous high-quality measurements of aerosol, cloud and radiative quantities made at the first EAST-AIRE baseline station at Xianghe, about 70 km east of Beijing over a period of one year (September 2004 to September 2005). It was found that the region is often covered by a thick layer of haze (with a yearly mean aerosol optical depth equal to 0.82 at 500 nm and maximum greater than 4) due primarily to anthropogenic emissions. An abrupt “cleanup” of the haze often took place in a matter of one day or less because of the passage of cold fronts. The mean single scattering albedo is approximately 0.9 but has strong day-to-day variations with maximum monthly averages occurring during the summer. Large aerosol loading and strong absorption lead to a very large aerosol radiative effect at the surface (the annual 24-hour mean values equals 24 W m⁻²), but a much smaller aerosol radiative effect at the top of the atmosphere (one tenth of the surface value). The boundary atmosphere is thus heated dramatically during the daytime, which may affect atmospheric stability and cloud formation. In comparison, the cloud radiative effect at the surface is only moderately higher (-41 W m⁻²) than the aerosol radiative effect at the surface.Item Effect of additives: organic-metal oxide nanocomposites for γ-ray sensors(SPIE, 2018-05-23) Singh, N. B.; Su, Ching Hua; Arnold, Bradley; Choa, Fow-Sen; Cooper, Christopher; Sova, Stacey; Gill, Puneet; Dayal, Vishall; Kelly, Lisa; Prasad, Narasimha; Smith, Paul; Cullum, BrianThe transition metal oxide embodied organic composites have great promise for high energy radiation detection. The interaction of high energy radiation such as γ-rays with the organic composite can generate photoelectric responses, Compton scattering and electron hole pairs, which can provide favorable properties to enhance the radiation detectivity of the composite. These effects along with changes of oxidation state of metal oxides, provide significant change in the electrical characteristics of composites due to radiation exposure. We have developed nickel oxide (NiO₂) nanoparticles embodied urea composite (urea-NiO₂), and determined effect of γ-radiation on the current – voltage characteristics in the frequency range of 100 Hz to 100,000Hz. In this paper, we describe the results of effect of additional oxidizing agent MnO₂ (urea-NiO₂-MnO₂) on the morphology, processing and current voltage characteristics due to exposure of Cs-137 γ-radiation. It was observed that addition of MnO₂ in urea-NiO₂ composite decreases the sensitivity of detection. However, urea-NiO₂-MnO₂ composite recovers to original properties after irradiation much faster than urea-NiO₂ composite.Item Effect of additives: γ-Ray sensors based on ionizing organic nanocompositesDayal, Vishall; Cooper, Christopher; Sova, Stacey; Gill, Puneet; Su, Ching-Hua; Arnold, Bradley; Choa, Fow-Sen; Kelly, Lisa; Cullum, Brian; Smith, Paul; Singh, N. B.We have developed ionizing organic based composites which have demonstrated great promise for radiation sensing. Nickel oxide has been proven as an active material for detecting high energy radiation. The oxidation state of unusual oxides such as nickel oxide in nanocomposites of ionizing organics changes much faster than thin film or bulk, and hence increases the sensitivity for radiation sensing. The resistivity of the oxide composite increases following sequential irradiation processes because of the decrease in holes' concentration. In this paper, we will present the effect of additional oxidizing agent on the morphology, processing and sensing of γ-ray by oxides - urea based nanocomposites. It was observed that addition of MnO₂ decreases the sensitivity. However, it recovers to original properties after irradiation much faster than undoped composites.