bei48482_FM

56

26 Fe

0 50 100 150 200 250

Binding energy per nucleon, MeV

2

4

6

8

10

Fusion

++E

Fission

++E

Mass number, A

Figure 11.12Binding energy per nucleon as a function of mass number. The peak at A4 corresponds

to the exceptionally stable^42 He nucleus, which is the alpha particle. The binding energy per nucleon

is a maximum for nuclei of mass number A56. Such nuclei are the most stable. When two light

nuclei join to form a heavier one, a process called fusion, the greater binding energy of the product

nucleus causes energy to be given off. When a heavy nucleus is split into two lighter ones, a process

called fission, the greater binding energy of the product nuclei also causes energy to be given off.

Nuclear Structure 401

involves a heat of vaporization of a mere 2260 kJ/kg, and even the heat given off by

burning gasoline is only 4.7  104 kJ/kg, 17 million times smaller.

Example 11.4

The binding energy of the neon isotope^2010 Ne is 160.647 MeV. Find its atomic mass.

Solution

Here Z10 and N10. From Eq. (11.7),

m(ZAX)[Zm(^11 H)Nm(n)]

m(^2010 Ne)[10 (1.007825 u)10 (1.008665)]19.992 u

Binding Energy per Nucleon

The binding energy per nucleonfor a given nucleus is an average found by dividing

its total binding energy by the number of nucleons it contains. Thus the binding energy

per nucleon for^21 H is (2.2 MeV) 2 1.1 MeV/nucleon, and for^20983 Bi it is (1640 MeV)

209 7.8 MeV/nucleon.

Figure 11.12 shows the binding energy per nucleon plotted against the number of

nucleons in various atomic nuclei. The greater the binding energy per nucleon, the

160.647 MeV



931.49 MeV u

Eb



931.49 MeV u

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