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The abundance of the chemical elements is a measure of the occurrences of the chemical elements relative to all other elements in a given environment. Abundance is measured in one of three ways: by mass fraction (in commercial contexts often called weight fraction), by mole fraction (fraction of atoms by numerical count, or sometimes fraction of molecules in gases), or by volume fraction.
Francium is one of the most unstable of the naturally occurring elements: its longest-lived isotope, francium-223, has a half-life of only 22 minutes. The only comparable element is astatine , whose most stable natural isotope, astatine-219 (the alpha daughter of francium-223), has a half-life of 56 seconds, although synthetic astatine-210 is ...
Sphalerite is a sulfide mineral with the chemical formula (Zn, Fe)S. [5] It is the most important ore of zinc.Sphalerite is found in a variety of deposit types, but it is primarily in sedimentary exhalative, Mississippi-Valley type, and volcanogenic massive sulfide deposits.
The adjacent table shows the result for [Ca 2+] and [H +] (in the form of pH) as a function of ambient partial pressure of CO 2 (K sp = 4.47 × 10 −9 has been taken for the calculation). At atmospheric levels of ambient CO 2 the table indicates that the solution will be slightly alkaline with a maximum CaCO 3 solubility of 47 mg/L.
Loss of potency requires periodic replacement of the source in radiotherapy and is one reason why cobalt machines have been largely replaced by linear accelerators in modern radiation therapy. [175] Cobalt-57 (Co-57 or 57 Co) is a cobalt radioisotope most often used in medical tests, as a radiolabel for vitamin B 12 uptake, and for the ...
Electron density or electronic density is the measure of the probability of an electron being present at an infinitesimal element of space surrounding any given point. It is a scalar quantity depending upon three spatial variables and is typically denoted as either () or ().
This can and does cause extremely complex behavior, such as the generation of plasma double layers, an object that separates charge over a few tens of Debye lengths. The dynamics of plasmas interacting with external and self-generated magnetic fields are studied in the academic discipline of magnetohydrodynamics .