Mass Defect

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Mass defect

The difference between the mass of an atom and the sum of the masses of its individual components in the free (unbound) state. The mass of an atom is always less than the total mass of its constituent particles; this means, according to Albert Einstein's well-known formula, that an energy of E = mc2 has been released in the process of combination, where m is the difference between the total mass of the constituent particles and the mass of the atom, and c is the velocity of light. The mass defect, when expressed in energy units, is called the binding energy, a term which is perhaps more commonly used. See Nuclear binding energy

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Mass Defect


the difference between the mass of the atom of a particular isotope, expressed in atomic mass units, and the mass number, which is equal to the number of nucleons in the nucleus of that isotope. The mass defect is associated with the binding energy of the nucleons in the nucleus; it characterizes the stability of the particular nucleus. Sometimes the mass defect related to a single nucleon is used; this is called the packing fraction.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

mass defect

[′mas ′dē‚fekt]
(nuclear physics)
The difference between the mass of an atom and the sum of the masses of its individual components in the free (unbound) state.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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Thus mass defect of deuteron must be infinitesimally small, only then masses of nucleons are same inside nucleus and outside nucleus.
Let in this case the mass defect is negligibly small i.e.