Atomic and Nuclear PhysicsDOE-HDBK-1019/1-93ATOMIC NATURE OF MATTERIf only the electrostatic and gravitational forces existed in the nucleus, then it would beimpossible to have stable nuclei composed of protons and neutrons. The gravitational forces aremuch too small to hold the nucleons together compared to the electrostatic forces repelling theprotons. Since stable atoms of neutrons and protons do exist, there must be another attractiveforce acting within the nucleus. This force is called the nuclear force.The nuclear force is a strong attractive force that is independent of charge. It acts equally onlybetween pairs of neutrons, pairs of protons, or a neutron and a proton. The nuclear force has avery short range; it acts only over distances approximately equal to the diameter of the nucleus(10-13cm). The attractive nuclear force between all nucleons drops off with distance much fasterthan the repulsive electrostatic force between protons.TABLE 3Forces Acting in the NucleusForceInteractionRangeGravitationalVery weak attractive forcebetween all nucleonsRelatively longElectrostaticStrong repulsive force betweenlike charged particles (protons)Relatively longNuclear ForceStrong attractive force betweenall nucleonsExtremely shortIn stable atoms, the attractive and repulsive forces in the nucleus balance. If the forces do notbalance, the atom cannot be stable, and the nucleus will emit radiation in an attempt to achievea more stable configuration.SummaryThe important information in this chapter is summarized on the following page.Rev. 0Page 9NP-01
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