Radioactive Decay Paths

Radioactivity involves the emission of particles from the nuclei. In the case of gamma emission, the nucleus remaining will be of the same chemical element, but for alpha, beta, and other radioactive processes, the nucleus will be transmuted into the nucleus of another chemical element. Each decay path will have a characteristic half-life, but some radioisotopes have more than one competing decay path.

Isotopes

The different isotopes of a given element have the same atomic number but different mass numbers since they have different numbers of neutrons. The chemical properties of the different isotopes of an element are identical, but they will often have great differences in nuclear stability. For stable isotopes light elements, the number of neutrons will be almost equal to the number of protons, but a growing neutron excess is characteristic of stable heavy elements. The element tin (Sn) has the most stable isotopes with 10, the average being about 2.6 stable isotopes per element.

Nuclear Forces

Within the incredibly small nuclear size, the two strongest forces in nature are pitted against each other. When the balance is broken, the resultant radioactivity yields particles of enormous energy.

Nuclear Size

The size of the nucleus compared to the size of the atom in which it resides is so small that it has invited a number of interesting comparisons. For example, the space inside an atom can be compared to the space in the solar system in a scale model. Scaling the gold nucleus suggests that the atomic radius is some 18,000 times the size of the nucleus. This great disparity in size was first discovered by Rutherford scattering of alpha particles off a thin gold foil. The extremity of this space comparison is highlighted by the fact that an atom with equal numbers of neutrons and protons, the nucleus comprises about 99.97% of the mass of the atom!

Experimental evidence suggests that nuclear matter is almost uniform density, so that the size of a nucleus can be estimated from its mass number.