from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Either of two decay products of thorium, mesothorium I, an isotope of radium, or mesothorium II, an isotope of actinium.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Any product of the radioactive decay of thorium, mainly isotopes of radium and actinium
from the GNU version of the Collaborative International Dictionary of English
- n. a radioactive isotope of radium (radium-228) with a half-life of 5.8 years. Also called mesothorium-1 or mesothorium I to distinguish it from a subsequent decay product, mesothorium II (actinium-228). It was discovered in 1907 by Otto Hahn as a decay product of thorium (produced by decay of thorium-232). Mesothorium-1 (radium-228) in turn produces actinium-228 (mesothorium-2) as the first product of its radioactive decay, and the actinium-228 in turn decays quickly (half-life of 6 hours) to thorium-228 (which is also called radiothorium; the thorium-228 has a half-life of 1.91 years, shorter than that of the radium-228). It was discovered and named before full recognition of the nature of isotopes of the elements, and was distinguished from other variants of radium by its half-life and mode of production and decay. It was also cheaper to prepare than other short-lived radium isotopes, and was thus sold commercially, for use, e.g. in making watch dials readable in the dark by painting the hands and hour marks with a self-luminous paint containing the radioactive substance; it is therefore often referred to (e.g. in regulatory legislation) as though distinct from radium. It was one of the isotopes believed responsible for radiation-induced diseases observed in industrial workers who painted radium on watch dials in the late 1950's and early 1960's. The primary isotope of radium (radium-226) has a half-life of 1620 years, and these isotopes with shorter half-lives proved difficult to isolate and study for the purpose of finding the cause of such diseases.
from The Century Dictionary and Cyclopedia
- n. A disintegration-product of thorium, intermediate between thorium and radiothorium.
Sorry, no etymologies found.
Produced by concentrated radium and mesothorium fluid diluted with distilled water, Radithor was packaged in half-ounce bottles and sold by the case of thirty.
University and there he qualified as a university lecturer in the spring of 1907, which year also saw his discovery of mesothorium.
Further investigation , however showed that it was impossible to separate those bodies from barium (although mesothorium, an isotope of radium, was readily separated in the same experiment), so that Hahn and Strassmann were forced to conclude that isotopes of barium (Z = 56) are formed as a consequence of the bombardment of uranium (Z = 92) with neutrons.
Thus were found the mesothorium now used by physicians and manufactured industrially, radio-thorium, ionium, protoactinium, radio-lead, and other substances.
I found the same reception at a factory of mesothorium which presented me with some material, and where the officials expressed the desire to help in my scientific work.
Many having other radio-elements are known already, the polonium, the mesothorium, the radiothorium, the actinium.
The greatly extended use of radium, together with the distinctly limited character of the world's known radium supplies, has led to some concern; and considerable investigation has been made of the possibilities of mesothorium as a substitute for radium in luminous paints.
Other radioactive elements have been discovered since: actinium (Debierne), radiothorium and mesothorium (Hahn), ionium (Boltwood), etc.
Radium, mesothorium, and the roentgenray are reported to have had in certain isolated cases a seemingly beneficial action.