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Summarizing Substructure of the Nucleus

Substructure of the Nucleus Summary

  • Two particles, both called nucleons, are found inside nuclei. The two types of nucleons are protons and neutrons; they are very similar, except that the proton is positively charged while the neutron is neutral. Some of their characteristics are given in this table and compared with those of the electron. A mass unit convenient to atomic and nuclear processes is the unified atomic mass unit (u), defined to be

    \(1 u=\text{1.6605}×{\text{10}}^{-\text{27}}\phantom{\rule{0.25em}{0ex}}\text{kg}=\text{931.46 MeV}/{c}^{2}.\)

  • A nuclide is a specific combination of protons and neutrons, denoted by

    \({}_{Z}^{A}{\text{X}}_{N}\phantom{\rule{0.25em}{0ex}}\text{or simply}{}^{A}\text{X,}\)

    \(Z\) is the number of protons or atomic number, X is the symbol for the element, \(N\) is the number of neutrons, and \(A\) is the mass number or the total number of protons and neutrons,


  • Nuclides having the same \(Z\) but different \(N\) are isotopes of the same element.
  • The radius of a nucleus, \(r\), is approximately


    where \({r}_{0}=1.2 fm\). Nuclear volumes are proportional to \(A\). There are two nuclear forces, the weak and the strong. Systematics in nuclear stability seen on the chart of the nuclides indicate that there are shell closures in nuclei for values of \(Z\) and \(N\) equal to the magic numbers, which correspond to highly stable nuclei.


atomic mass

the total mass of the protons, neutrons, and electrons in a single atom

atomic number

number of protons in a nucleus

chart of the nuclides

a table comprising stable and unstable nuclei


nuclei having the same \(Z\) and different \(N\)s

magic numbers

a number that indicates a shell structure for the nucleus in which closed shells are more stable

mass number

number of nucleons in a nucleus


a neutral particle that is found in a nucleus


the particles found inside nuclei


a region consisting of protons and neutrons at the center of an atom


a type of atom whose nucleus has specific numbers of protons and neutrons


the positively charged nucleons found in a nucleus

radius of a nucleus

the radius of a nucleus is \(r={r}_{0}{A}^{1/3}\)

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