Atomic and Nuclear PhysicsDOE-HDBK-1019/1-93NUCLEAR FISSIONBindingEnergyPer Nucleon(BE/A)As the number of particles in a nucleus increases, the total binding energy also increases. Therate of increase, however, is not uniform. This lack of uniformity results in a variation in theamount of binding energy associated with each nucleon within the nucleus. This variation in thebinding energy per nucleon (BE/A) is easily seen when the average BE/A is plotted versus atomicmass number (A), as shown in Figure 20.Figure 20 Binding Energy per Nucleon vs. Mass Number Figure 20 illustrates that as the atomic mass number increases, the binding energy per nucleondecreases for A > 60. The BE/A curve reaches a maximum value of 8.79 MeV at A = 56 anddecreases to about 7.6 MeV for A = 238. The general shape of the BE/A curve can be explainedusing the general properties of nuclear forces. The nucleus is held together by very short-rangeattractive forces that exist between nucleons. On the other hand, the nucleus is being forced apartby long range repulsive electrostatic (coulomb) forces that exist between all the protons in thenucleus. Rev. 0Page 53NP-01
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