4 3
20. (a) The first step is to add energy to produce He p + H, which  to make the electrons  balance
4 1 3
 may be rewritten as He H+ H. The energy needed is "E1 =(m3 + m1 - m4 )c2 =
H H He
(3.01605 u + 1.00783 u - 4.00260 u)(931.5MeV/u) = 19.8MeV. The second step is to add energy to
3
produce H n+2H. The energy needed is "E2 =(m2 +mn -m3 )c2 =(2.01410 u+1.00867 u-
H H
2
3.01605 u)(931.5MeV/u) = 6.26 MeV. The third step: H p + n, which  to make the electrons
2 1
 balance  may be rewritten as H H+n. The work required is "E3 =(m1 +mn -m2 )c2 =
H H
(1.00783 u + 1.00867 u - 2.01410 u)(931.5MeV/u) = 2.23 MeV.
(b) The total binding energy is "Ebe = "E1 +"E2 +"E3 = 19.8MeV + 6.26 MeV + 2.23 MeV =
28.3MeV.
(c) The binding energy per nucleon is "Eben ="Ebe/A =28.3MeV/4 =7.07 MeV.