Calculate the Q-value in the following decays:
(a) `^19 O rarr ^19 F + e + vec v`.
(b) `^25 A1 rarr ^25 Mg + e^+ + v`.
The atomic masses needed are as follows :
`^19 O 19.003576 u`
`^19 F 18.998403 u`
`^25 A1 24.990432 u`
`^25 Mg 24.985839 u`

Explanation

The Q-value of `beta^(-1) -dacay` is`
`Q = [m(^19 O) - m (^19 F)] c^2`
`= [19.003576 u - 18.998403 u] - 2 xx 0.511 MeV c^(-2)] c^2`
`=(0.004593 u) (931 MeV u^(-1) - 1.022 MeV`
`= 4.276 MeV - 1.022 MeV = 3.254 MeV`.