Question

A plot of the number of neutrons (N) against the number of protons (P) of stable nuclei exhibits upward deviation from linearity for atomic number, Z > 20. For an unstable nucleus having $\frac{N}{P}$ ratio less than 1, the possible mode(s) of decay is(are)

• A. ${\beta }^{-}$ - decay ($\beta$ emission)
• B. Orbital or K-electron capture
• C. Neutron emission
• D. ${\beta }^{+}$ - decay (positron emission)

Answer 1

Answer: (B), (D)

${\beta }^{+}$ - decay (positron emission)

$\frac{n}{p}<1$

Positron emission

${}_a{X}^b{\to }_{+1}^{0}e{+}_{a-1}{Y}^b$

K - electron capture

${}_a{X}^b{+}_{-1}{e}^0{\to }_{a-1}{Y}^b$

Both processes cause an increase in the $\frac{n}{p}$ ratio towards 1, thus stabilising the nucleus.