mass number
the total number of neutrons and protons in the nucleus of a particular atom.
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
Mass number
The mass number A of an atom is the total number of its nuclear constituents, or nucleons, as the protons and neutrons are collectively called. The mass number is placed before and above the elemental symbol, thus 238U. The mass number gives a useful rough figure for the atomic mass; for example, 1H = 1.00814 atomic mass units (amu), 238U = 238.124 amu, and so on. See Atomic number
McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.
mass number
Symbol: A. The number of protons and neutrons (i.e. nucleons) in the nucleus of a particular atom. It is the number closest to the mass of a nuclide in atomic mass units, i.e. in units equal to 1/12 of the mass of a carbon-12 atom. See also atomic number.Collins Dictionary of Astronomy © Market House Books Ltd, 2006
mass number
[′mas ‚nəm·bər] (nuclear physics)
The sum of the numbers of protons and neutrons in the nucleus of an atom or nuclide. Also known as nuclear number; nucleon number.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.
Mass Number
the number of nucleons (protons and neutrons) in the atomic nucleus; designated by the letter A and usually indicated as a superscript to the left of the symbol of an element. The mass number and charge of a nucleus Z, expressed in units of elementary electric charge, determine the composition of the atomic nucleus: Z protons and (A — Z) neutrons. The mass of any atom, expressed in atomic mass units and rounded to the nearest whole number, is equal to its mass number.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.