51.
(a) For the first reaction
Q
1
=
(m
Ra
− m
Pb
− m
C
)c
2
=
(223.01850 u
− 208.98107 u − 14.00324 u)(931.5 MeV/u)
=
31.8 MeV ,
and for the second one
Q
2
=
(m
Ra
− m
Rn
− m
He
)c
2
=
(223.01850 u
− 219.00948 u − 4.00260 u)(931.5 MeV/u)
=
5.98 MeV .
(b) From U
∝ q
1
q
2
/r, we get
U
1
≈ U
2
q
Pb
q
C
q
Rn
q
He
= (30.0 MeV)
(82e)(6.0e)
(86e)(2.0e)
= 86 MeV .