from The American Heritage® Dictionary of the English Language, 5th Edition.
- noun A radioactive element found in uranium ores, used in equilibrium with its decay products as a source of alpha rays. Its longest lived isotope is Ac-227 with a half-life of 21.77 years. Atomic number 89; melting point 1,050°C; boiling point 3,198°C; specific gravity (calculated) 10.07; valence 3. cross-reference: Periodic Table.
from The Century Dictionary.
- noun A supposed chemical element found associated with zinc. Its chemical and physical properties have not been fully investigated.
- noun A radioactive substance found by Debierne to exist in the residues remaining from pitchblende after the extraction of the uranium: a new radio-element closely related in its chemical behavior to lanthanum, from which it has not as yet been found possible to separate it completely.
from the GNU version of the Collaborative International Dictionary of English.
- noun (Chem.) A supposed metal, said by Phipson to be contained in commercial zinc; -- so called because certain of its compounds are darkened by exposure to light.
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- noun a
radioactive, metallic chemical element(symbol: Ac) with an atomic numberof 89; found in uranium ores
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- noun a radioactive element of the actinide series; found in uranium ores
from The American Heritage® Dictionary of the English Language, 4th Edition
from Wiktionary, Creative Commons Attribution/Share-Alike License
With Ramsay's consent, Hahn had taken with him the radiothorium he separated from samples of barium chloride and the actinium that he and a collaborator had earlier proved to be identical to the new element that the German chemist Friedrich Giesel had named emanium.
Hahn's radiothorium and actinium salts also followed him to Emil Fischer's laboratory in Berlin. 30
In collaboration with Rona, she applied her method to the study of the ranges of alpha particles emitted from actinium and polonium. 6 7
In France, Debierne had discovered actinium and Giesel claimed to have found a different element, emanium.
M. and Mme. Curie, radium was also discovered by them in collaboration with Bémont, and actinium by Debierne.
Considerable work, guided by the theory of radioactive transformations, has led to approximately 30 new radioactive elements being envisaged, classified in 4 series according to the primary substance: these series are uranium, radium, thorium and actinium.
Other radioactive elements have been discovered since: actinium (Debierne), radiothorium and mesothorium (Hahn), ionium (Boltwood), etc.
This at once offered an explanation of the fact observed by Debierne that actinium as well as radium produced helium.
It is likely that the actinium series is related to that of radium.
And it is not inconceivable that the still more unstable emanation from the matter named actinium by Debierne and emanium by Giesel may be found to possess an even higher atomic weight than uranium; judging by the phenomenon of brilliant illumination when a preparation of emanium is held above a screen of zinc sulphide, the impression is formed that a very dense matter is falling down on the screen.