although the nuclear model of the atom
71radioactivity — /ray dee oh ak tiv i tee/, n. Physics, Chem. the phenomenon, exhibited by and being a property of certain elements, of spontaneously emitting radiation resulting from changes in the nuclei of atoms of the element. Also called activity. [1895… …
72Atomic nucleus — A figurative depiction of the helium 4 atom with the electron cloud in shades of gray. In the nucleus, the two protons and two neutrons are depicted in red and blue. This depiction shows the particles as separate, whereas in an actual helium atom …
73performing arts — arts or skills that require public performance, as acting, singing, or dancing. [1945 50] * * * ▪ 2009 Introduction Music Classical. The last vestiges of the Cold War seemed to thaw for a moment on Feb. 26, 2008, when the unfamiliar strains …
74Bohr, Niels — ▪ Danish physicist Introduction in full Niels Henrik David Bohr born Oct. 7, 1885, Copenhagen, Den. died Nov. 18, 1962, Copenhagen Danish physicist who was the first to apply the quantum theory, which restricts the energy of a system to… …
75Neutrino — For other uses, see Neutrino (disambiguation). Neutrino/Antineutrino The first use of a hydrogen bubble chamber to detect neutrinos, on November 13, 1970. A neutrino hit a proton in a hydrogen atom. The collision occurred at the point where three …
76Photon — This article is about the elementary particle of light. For other uses, see Photon (disambiguation). Photon Photons emitted in a coherent beam from a laser Composition Elementary particle …
77transuranium element — Any of the chemical elements after uranium in the periodic table (with atomic numbers greater than 92). All are radioactive (see radioactivity), with half lives ranging from tens of millions of years to fractions of a millisecond. Only two,… …
78chemical element — Introduction also called element, any substance that cannot be decomposed into simpler substances by ordinary chemical processes. Elements are the fundamental materials of which all matter is composed. This article considers the… …
79John Dalton — For other people named John Dalton, see John Dalton (disambiguation). John Dalton …
80Ozone depletion — Image of the largest Antarctic ozone hole ever recorded (September 2006) Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth s… …
