Environmental Engineering Reference
In-Depth Information
2.5
A Survey of Nuclear Properties
The binding energy per nucleon BE has been plotted in Figure 1.5. Nuclei are
characterized by a line of stability approximating
Z¼N
up to
Z
near 100 as shown in
Figure 2.5. The stability of large nuclei disappears beyond
Z¼
100 as the Coulomb
repulsion energy increases. As a function of nucleon number,
A
, the binding energy
BE per particle rises from zero to a maximum near
A¼
56 and then gradually
decreases. Nuclei beyond
A¼
260 or so are unstable.
The basic properties of the nuclei can be understood in simple terms, based upon
the strong nuclear attractive force, leading to a binding energy
U
o
in the vicinity of
12MeVper nucleon. Nuclei are nearly spherical, which is expectedwith a short-range
attractive force, similar in principle to the intermolecular force in a drop of water.
Water drops are spherical to minimize the number of molecules, at the surface,
which will not have a full set of near neighbors. A liquid dropmodel was used early to
understand aspects of nuclear
ssion. As in a water droplet, particles near the surface
are less strongly bound, and this effect can be described as a surface energy.
Figure 2.5 A survey of stable nuclei. The dotted line corresponds toN¼Z or to A¼2Z. Nuclei for Z
much larger than 100 are unstable because of Coulomb repulsion.