| element | <chemistry> One of the 103 known chemical substances that cannot be divided into simpler substances by chemical means. A substance whose atoms all have the same atomic number. Examples: hydrogen, lead, uranium.(See atom, matter, nuclide.) (16 Dec 1997) |
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| elementary bodies | Old term for virions, especially the largest virus particles, visible by light microscopy when stained. Synonym: platelet. (05 Mar 2000) |
| elementary granule | A particle of blood dust, or haemoconia. (05 Mar 2000) |
| elementary particle interactions | The interactions of particles responsible for their scattering and transformations (decays and reactions). Because of interactions, an isolated particle may decay into other particles. Two particles passing near each other may transform, perhaps into the same particles but with changed momenta (elastic scattering) or into other particles (inelastic scattering). Interactions fall into three groups: strong, electromagnetic, and weak. (12 Dec 1998) |
| elementary particles | <radiobiology> at a nuclear-energy level: electron & positron - seem to be stable, proton - thought to be stable, life greater than 10^30 sec, neutron - decays in ?6 min unless its in a nucleus, which often extends its life. Other particles important for nuclear energy: Muon, neutrino (m, e, tau), photon, Muonic atoms, Pi-meson antiparticles (09 Oct 1997) |
| elementary step | <chemistry> Reaction mechanisms are broken down into elementary steps. For each step the the reactants are directly involved in forming the transition state. Therefore a rate law can be written from an elementary step but not from an overall reaction. (09 Jan 1998) |
| elements | Simple substances which cannot be decomposed by chemical means. They are made up of atoms which are alike in their peripheral electronic configurations, their chemical properties, and in the number of protons in their nuclei. They may differ in the number of neutrons in their nuclei. (12 Dec 1998) |
| elements, radioactive | Chemical elements which spontaneously transmute into another element with corpuscular or electromagnetic radiation. The natural radioactive elements are all those with an atomic number above 83, and some other elements, such as potassium (atomic number 19) and rubidium (atomic number 7), which are very weakly radioactive. (12 Dec 1998) |
| elemi | A fragrant gum resin obtained chiefly tropical trees of the genera Amyris and Canarium. A. Elemifera yields Mexican elemi; C. Commune, the Manila elemi. It is used in the manufacture of varnishes, also in ointments and plasters. Origin: Cf. F. Elemi, It. Elemi, Sp. Elemi; of American or Oriental. Origin. Source: Websters Dictionary (01 Mar 1998) |
| elemin | <chemistry> A transparent, colourless oil obtained from elemi resin by distillation with water; also, a crystallizable extract from the resin. Source: Websters Dictionary (01 Mar 1998) |