Size of the Nucleus
The nucleus is the small, dense region consisting of protons and neutrons at the center of an atom. The atomic nucleus was discovered in 1911 by Ernest Rutherford.
We have already discussed the “scale” of things in the microscopic world in general and nuclei in particular. The unit of length most appropriate to nuclei and particles is, therefore, Fermi (10-15 m). All information about the external (physical) world comes from scattering. We see the external world by scattering of light on objects we want to see; the scattered light is captured by the eyes and an image is formed on the retina. We need smaller wavelengths than the visible light to see smaller objects; the scattered waves should then be captured by appropriate detectors and analyzed for the information about the shape and size of the objects which could be nuclei also. Scattering by light (electro-magnetic waves) or, high energy particles (matter waves) is widely used to gather information about the shape and size of nuclei.
Let us first have a look at the simplest scattering phenomenon namely the classical scattering of a light particle from a rigid hard sphere to understand how one may get the size of a nucleus from the scattering data. The Rutherford scattering or Coulomb scattering will be considered next
Nuclear Units
Nuclear energies are very high compared to atomic processes, and need larger units. The most commonly used unit is the MeV.
1 electron volt = 1eV = 1.6 x 10-19 joules
1 MeV = 106 eV; 1 GeV = 109 eV; 1 TeV = 1012 eV
However, the nuclear sizes are quite small and need smaller units:
Atomic sizes are on the order of 0.1 nm = 1 Angstrom = 10-10 m
Nuclear sizes are on the order of femtometers which in the nuclear context are usually called fermis:
1 fm = 10-15m