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thorium
(Encyclopedia)thorium thôrˈēəm [key] [from Thor], radioactive chemical element; symbol Th; at. no. 90; mass number of most stable isotope 232; m.p. about 1,750℃; b.p. about 4,790℃; sp. gr. 11.7 at 20℃; va...nucleosynthesis
(Encyclopedia)nucleosynthesis or nucleogenesis, in astronomy, production of all the chemical elements from the simplest element, hydrogen, by thermonuclear reactions within stars, supernovas, and in the big bang at...plutonium
(Encyclopedia)plutonium plo͞otōˈnēəm [key], radioactive chemical element; symbol Pu; at. no. 94; mass no. of most stable isotope 244; m.p. 641℃; b.p. 3,232℃; sp. gr. 19.84 at 20℃; valence +3, +4, +5, or ...rutherfordium
(Encyclopedia)rutherfordium rŭᵺˌərfôrˈdēəm [key], artificially produced radioactive chemical element; symbol Rf; at. no. 104; mass number of most stable isotope 265; m.p., b.p., and sp. gr. unknown; valenc...oganesson
(Encyclopedia)oganesson ōˈgənĕsˌən [key], artificially produced radioactive chemical element; symbol Og; at. no. 118; mass number of most stable isotope 294; m.p., b.p., sp. gr., and valence unknown. Situated...Kamen, Martin David
(Encyclopedia)Kamen, Martin David kāˈmən [key], 1913–2002, American biochemist, b. Toronto, Canada, grad. Univ. of Chicago (B.S., Ph.D. 1937). He discovered carbon-14, the radioactive isotope of carbon used to...fermium
(Encyclopedia)fermium fûrˈmēəm [key] [for Enrico Fermi], artificially produced radioactive chemical element; symbol Fm; at. no. 100; mass no. of most stable isotope 257; m.p. 1,527℃; b.p. and sp. gr. unknown;...radium
(Encyclopedia)radium rāˈdēəm [key] [Lat. radius=ray], radioactive metallic chemical element; symbol Ra; at. no. 88; mass number of most stable isotope 226; m.p. 700℃; b.p. 1,140℃; sp. gr. about 6.0; valence...nucleus, in physics
(Encyclopedia)nucleus, in physics, the extremely dense central core of an atom. Following the discovery of radioactivity by A. H. Becquerel in 1896, Ernest Rutherford identified two types of radiation given off b...Meitner, Lise
(Encyclopedia)Meitner, Lise lēˈzə mītˈnər [key], 1878–1968, Austrian-Swedish physicist and mathematician. She was professor at the Univ. of Berlin (1926–33). A refugee from Germany after 1938, she became ...Browse by Subject
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