Environmental geochemistry of radioactive contamination.

This report attempts to describe the geochemical foundations of the behavior of radionuclides in the environment. The information is obtained and applied in three interacting spheres of inquiry and analysis: (1) experimental studies and theoretical calculations, (2) field studies of contaminated and natural analog sites and (3) model predictions of radionuclide behavior in remediation and waste disposal. Analyses of the risks from radioactive contamination require estimation of the rates of release and dispersion of the radionuclides through potential exposure pathways. These processes are controlled by solubility, speciation, sorption, and colloidal transport, which are strong functions of the compositions of the groundwater and geomedia as well as the atomic structure of the radionuclides. The chemistry of the fission products is relatively simple compared to the actinides. Because of their relatively short half-lives, fission products account for a large fraction of the radioactivity in nuclear waste for the first several hundred years but do not represent a long-term hazard in the environment. The chemistry of the longer-lived actinides is complex; however, some trends in their behavior can be described. Actinide elements of a given oxidation state have either similar or systematically varying chemical properties due to similarities in ionic size, coordination number, valence, and electron structure. In dilute aqueous systems at neutral to basic pH, the dominant actinide species are hydroxy- and carbonato-complexes, and the solubility-limiting solid phases are commonly oxides, hydroxides or carbonates. In general, actinide sorption will decrease in the presence of ligands that complex with the radionuclide; sorption of the (IV) species of actinides (Np, Pu, U) is generally greater than of the (V) species. The geochemistry of key radionuclides in three different environments is described in this report. These include: (1) low ionic strength reducing waters from crystalline rocks at nuclear waste research sites in Sweden; (2) oxic water from the J-13 well at Yucca Mountain, Nevada, the site of a proposed repository for high level nuclear waste (HLW) in tuffaceous rocks; and (3) reference brines associated with the Waste Isolation Pilot Plant (WIPP). The transport behaviors of radionuclides associated with the Chernobyl reactor accident and the Oklo Natural Reactor are described. These examples span wide temporal and spatial scales and include the rapid geochemical and physical processes important to nuclear reactor accidents or industrial discharges as well as the slower processes important to the geologic disposal of nuclear waste. Application of geochemical information to remediating or assessing the risk posed by radioactive contamination is the final subject of this report. After radioactive source terms have been removed, large volumes of soil and water with low but potentially hazardous levels of contamination may remain. For poorly-sorbing radionuclides, capture of contaminated water and removal of radionuclides may be possible using permeable reactive barriers and bioremediation. For strongly sorbing radionuclides, contaminant plumes will move very slowly. Through a combination of monitoring, regulations and modeling, it may be possible to have confidence that they will not be a hazard to current or future populations. Abstraction of the hydrogeochemical properties of real systems into simple models is required for probabilistic risk assessment. Simplifications in solubility and sorption models used in performance assessment calculations for the WIPP and the proposed HLW repository at Yucca Mountain are briefly described

Pengantar Fisika kesehatan

xvii.629 hal.;ill.;24 c

Pengaruh econimic value added, market value added, dan operating leverage terhadap return saham

ABSTRAKSITujuan penelitian ini adalah: 1). Untuk mengetahui pengaruh Economic Value Added (EVA) terhadap Return saham pada perusahaan pertambangan, 2). Untuk mengetahui pengaruh Market Value Added (MVA) terhadap Return Saham perusahaan pertambangan, 3) Untuk mengetahui pengaruh Operating Leverage terhadap Return saham perusahaan pertambangan.Populasi dalam penelitian ini ialah semua sektor industri pada perusahaan pertambangan yang terdaftar di BEI Periode 2015-2017. Metode yang digunakan dalam menganalisis penelitian ini ialah uji asumsi klasik dan uji regresi linier berganda. Dengan uji t dan uji F sebagai penguji hipotesis. Hasil penelitian ini membuktikan bahwa Economic Value Added (EVA) berpengaruh positif dan tidak signifikan, Market Value Added (MVA) berpengaruh posistif dan tidak signifikan, Operating Leverage berpengaruh positif dan tidak signifikan. Kata kunci: Harga Saham, Return Saham, Economic Value Added, Market Value Added, Operating Leverage.ALBSTRACKThe objectives of this study are: 1). To find out the Economic Value Added effect on company stock returns (EVA), 2). To find out the Market Value Added (MVA) to the stock returns of mining companies, 3) to find out operating leverage against stock returns of mining companies. The population on this study were all industrial sectors of mining companies listed on the IDX for the period 2015-2017. The method used in this stud is the classic assumption test and multiple linear regression. With t test and f test as hypothesis testers. The result of this study Economic Value Added (EVA) has a positive and not significant effect, Market Value Added (MVA) has a positive and not significant effect, operating leverage has a positive and not significant effect. Keywords: stock prices, stock returns, economic value added, market value added, operating leverage