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 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 56 and then gradually
decreases. Nuclei beyond 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.
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