摘要:

Ionizing radiation is utilized in many industrial, medical and research applications. The term ionizing radiation implies that the interaction of the radiation with the object of interest occurs at the atomic level, through the removal of electrons from atoms and molecules. In trying to understand, enhance and develop technologies that utilize ionizing radiation, atomic data and tools to utilize these data sets are essential. In this paper some current applications of ionizing radiation are discussed. The computational tools applied to these situations are outlined. Currently available data sets are reviewed. Data needs are discussed as are some of the efforts underway at the National Institute of Standards and Technology (NIST) to enhance both data and tools. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516319

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

This paper provides a brief summary of recent advances in track structure simulation of low energy alpha‐particles. A description is given for biophysical modelling of the interaction of radiation in DNA in terms of energy deposition and complexity of DNA damage. Track simulations allow estimation of the molecular spectrum of DNA damage. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516320

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

All types of ionizing radiation interact with material by producing atomic or molecular ions, excited states, and secondary electrons. Still, different types of radiation lead to quite different yields of biological damage. It is generally believed that the spatial distributions of ionization and excitation produced by the slowing down of charged particles, particularly electrons, govern the yields of bioactive molecular species. The assessment of these spatial patterns of ionization and excitation depend largely on the production cross sections for secondary electrons, the energies and angular correlations of their production, and the subsequent differential cross sections for their energy loss in the media of interest. The most thorough assessment of spatial patterns of energy deposition by charged particles is obtained using Monte Carlo simulation of charged particle track structure based on the available database of interaction cross sections. This step‐by‐step analysis of the interactions of charged particles, from their initial energies until stopped in the medium, provides detailed information on the spatial distribution of the products of ionization from which subsequent chemical and biochemical reactions can be assessed. Over the years a substantial database has been developed describing the interaction of fast, “bare” charged particles, e.g., electrons, protons, and alpha particles, with atomic and molecular targets. However, as charged particles slow they enter an energy regime where additional energy‐loss channels open and the availability of data is often limited; interest in this region is also intensified because the biological effectiveness of these particles can increase as their energy decreases. This presentation will focus on the special needs for data involving low‐energy electrons and ions, i.e., slowing protons, alpha particles and heavier ions, in a biological environment. A brief discussion of the availability of cross sections will be presented and areas of need for additional data will be discussed. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516321

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

This paper gives a summary of recent results about the replacement of mercury in high pressure discharge lamps by metallic zinc. Actually, this topic is of high relevance for the lighting industry due to the need of more environmentally friendly products. The work presented here is supported by the German government under contract no. 13N8072. Pure zinc/argon discharges as well as lamps including zinc or mercury and metal halide additives are investigated. Experimental data are compared with model calculations of the energy balance involving the transport of heat and radiation. Since the excitation energies of relevant zinc transistions are lower than for mercury, axis temperatures of pure zinc lamps are about 300 K below the value of mercury arcs. In addition, the thermal conductivity of zinc including the contribution of radiation diffusion is larger than compared to mercury. From lamp voltage measurements it is found that the cross section for elastical electron scattering by zinc atoms is about the same as for mercury. When adding metal halides to a pure zinc discharge with argon as a starting gas, i.e. NaI, TlI, DyI3, axis temperatures decrease to about 5100 K due to strong radiation cooling. In order to obtain sufficiently large lamp voltages, wall temperatures of more than 1300 K are adjusted by means of polycrystalline aluminaoxide (Al2O3) as a wall material. Electrical field strenghts of 6.0 V/mm and 8.6 V/mm are measured for metal halide lamps containing zinc or mercury, respectively. The light technical data of the discharges are very close, since mercury and zinc do not contribute significantly to the radiation in the visible range. Efficacies of up to 93 lm/W and 100 lm/W are found in metal halide lamps with zinc and mercury, respectively. Consequently, zinc turns out to be an attractive replacer for mercury in this type of lamp not only from an environmental point of view. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516322

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

Numerical models have provided insight into the operation of “standard” fluorescent lamps for more than 40 years. Recent developments in the lighting industry have led to products with much higher power loadings, for which modeling has been less successful in reproducing the experimental results. One of the potential weaknesses of the models is the absence of fundamental data to describe important phenomena in these “highly loaded lamps”. The current state of our knowledge of available data is reviewed, together with an overview of the recently completed ALITE 1 project to reexamine the fundamental properties of fluorescent lamp operation. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516323

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

Different aspects of the modeling of moderate pressure hydrogen and hydrogen methane plasma obtained under conditions relevant to diamond thin films deposition are discussed. First, a collisional‐radiative model (CRM) of H2plasmas is presented and used in the frame of a quasi‐homogenous plasma assumption to determine the main collisional phenomena that govern hydrogen discharges. The CRM was then used to build up more simplified thermo‐chemical model that was used as a starting point for the development of a transport model for the more complex H2/CH4plasmas. These have been investigated with a one dimensional (1D) that describes the plasma flow on the symmetry axis of a bell jar reactor. Discussion on the impact of the collisional data used in the different models is especially emphasized. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516324

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

The mechanism of VUV production in an AC‐PDP was theoretically studied, and ways to increase VUV production efficiency were discussed. It was then shown that precise and dynamic control of the non‐uniform and non‐steady discharge‐radiation process will become even more important in the future development of new AC‐PDP technologies. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516325

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

This paper is related to an overview of data needs to calculate thermodynamic and transport properties of thermal plasmas in local thermodynamic equilibrium (LTE) and in non‐LTE (when the electron kinetic temperature is assumed to be different of that of heavy species). Methods of calculation of plasma composition are first presented at equilibrium as well as in non‐equilibrium conditions with the data needs for partition functions and kinetic reaction rates. Then a particular attention is paid to transport coefficients in non‐equilibrium thermal plasmas with the data needs: interaction potentials, collision cross sections&ellip;. The comparison between the non‐equilibrium simplified theory of transport properties of Devoto and Bonnefoi and that recently developed by Rat et al is made. The influence of the plasma composition on transport coefficients is also presented. Finally, two‐temperature combined diffusion coefficients are shown in an argon‐hydrogen plasma highlighting the mass conservation. Such calculations show that, besides the data uncertainties, the calculation method plays a critical role in the values of plasma thermodynamic and transport properties, especially in non‐equilibrium conditions. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516326

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

SiO2etching is done by using fluorocarbon gases to deposit a fluoropolymer on the underlying silicon. This deposit enhances the etching selectivity of SiO2over silicon or silicon nitride. CF2radicals are used as the main gas precursor for polymer deposition. In a conventional gas plasma, however, the CF2radicals and other radicals (high‐molecular‐weight‐radicals: CxFy) lead to polymerization. This condition causes microloading and etching‐stop in high‐aspect contact‐hole patterning due to the sidewall polymerization during SiO2etching processes. Conversely, by using new fluorocarbon gas chemistries (C2F4/CF3I), we achieved selective radical generation of CF2and eliminated high‐molecular‐weight radicals. Under this condition, microloading‐free and etching‐stop‐free high‐aspect‐ratio contact‐hole patterning of SiO2was accomplished. Thus, the higher molecular weight radicals play an important role in the sidewall polymerization in contact holes because these radicals have a higher sticking coefficient than CF2radicals. Selective generation of CF2radicals and suppression of CxFyradicals are thus necessary to eliminate microloading and etching‐stop in the formation of high‐aspect‐ratio contact holes. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516327

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

Since fifteen years, an increasing interest has been devoted to removal of atmospheric pollutant by non‐thermal plasmas achieved using e‐beams or pulsed discharges, for the nitrous oxides the so‐called de‐NOxprocess, or for Volatils Organic Compounds, the so‐called de‐VOC process. However the physical and chemical mechanisms involved are not easy to understand: molecules or gas mixtures are quite complex, and the transient plasma created by the type of discharge often used, dielectric barrier or corona ones, is non homogeneous in space. In this paper is discussed some data needs for understanding of the NO‐removal process and the destruction of some selected VOC molecules, TCE and TCA, by pulsed discharge plasmas. Some experimental studies performed to get insight into the discharge plasma kinetic involved in the pollutant removal are presented, in particular about the hydroxyl radical OH which play an important role in this kinetic. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1516328

出版商:AIP    

年代:1902

数据来源: AIP