Atomic and Nuclear Physics DOE-HDBK-1019/1-93 ATOMIC NATURE OF MATTER r    = (1.25 x 10 -13 cm) A^1/3 where: r    = radius of the nucleus (cm) A  = atomic mass number (dimensionless) The  values  of  the  nuclear  radii  for  some  light,  intermediate,  and  heavy  nuclides  are  shown  in Table 2. TABLE 2 Calculated Values for Nuclear Radii Nuclide Radius of Nucleus 1 1 H 1.25 x 10 -13 cm 10 5 B 2.69 x 10 -13 cm 5 2 6 6 Fe 4.78 x 10 -13 cm 17 7 8 2 Hf 7.01 x 10 -13 cm 23 9 8 2 U 7.74 x 10 -13 cm 25 9 2 8 Cf 7.89 x 10 -13 cm From the table, it is clear that the radius of a typical atom (e.g. 2 x 10 -8 cm) is more than 25,000 times larger than the radius of the largest nucleus. Nuclear Forces In the Bohr model of the atom, the nucleus consists of positively-charged protons and electrically- neutral neutrons.   Since both protons and neutrons exist in the nucleus, they are both referred to as  nucleons.    One  problem  that  the  Bohr  model  of  the  atom  presented  was  accounting  for  an attractive force to overcome the repulsive force between protons. Two forces present in the nucleus are (1) electrostatic forces between charged particles and (2) gravitational  forces  between  any  two  objects  that  have  mass.    It  is  possible  to  calculate  the magnitude of the gravitational force and electrostatic force based upon principles from classical physics. Rev. 0 Page 7 NP-01