Atomic and Nuclear Physics
DOE-HDBK-1019/1-93
MASS DEFECT AND BINDING ENERGY
MASS DEFECT AND BINDING ENERGY
The separate laws of Conservation of Mass and Conservation of Energy are not
applied strictly on the nuclear level. It is possible to convert between mass and
energy. Instead of two separate conservation laws, a single conservation law
states that the sum of mass and energy is conserved. Mass does not magically
appear and disappear at random. A decrease in mass will be accompanied by a
corresponding increase in energy and vice versa.
EO 1.7
DEFINE the following terms:
a.
Mass defect
b.
Binding energy
EO 1.8
Given the atomic mass for a nuclide and the atomic masses of
a neutron, proton, and electron, CALCULATE the mass defect
and binding energy of the nuclide.
Mass Defect
Careful measurements have shown that the mass of a particular atom is always slightly less than
the sum of the masses of the individual neutrons, protons, and electrons of which the atom
consists. The difference between the mass of the atom and the sum of the masses of its parts is
called the mass defect (Dm). The mass defect can be calculated using Equation (1-1). In
calculating the mass defect it is important to use the full accuracy of mass measurements because
the difference in mass is small compared to the mass of the atom. Rounding off the masses of
atoms and particles to three or four significant digits prior to the calculation will result in a
calculated mass defect of zero.
Dm = [ Z(mp + me) + (A-Z)mn ] - matom
(1-1)
where:
Dm
=
mass defect (amu)
mp
=
mass of a proton (1.007277 amu)
mn
=
mass of a neutron (1.008665 amu)
me
=
mass of an electron (0.000548597 amu)
matom
=
mass of nuclide AZ X (amu)
Z
=
atomic number (number of protons)
A
=
mass number (number of nucleons)
Rev. 0
Page 17
NP-01
