Question

Neutron-rich unstable nuclides undergo

• A. $β^– (negatron) decay$
• B. $β^ + (positron) decay$
• C. α-decay
• D. electron capture

Answer 1

The Correct Option is A

Neutron-Rich Unstable Nuclides and β⁻ Decay

Neutron Excess and Instability 

Neutron-rich unstable nuclides have an excess of neutrons, making them unstable. To achieve stability, they undergo β⁻ (negatron) decay.

β⁻ Decay Process

In β⁻ decay, a neutron (\( n \)) is converted into a proton (\( p \)), emitting an electron (\( e^- \)) and an antineutrino (\( \bar{\nu}_e \)):

\[ n \rightarrow p + e^- + \bar{\nu}_e \]

Explanation

• The neutron transforms into a proton, increasing the proton-to-neutron ratio.
• An electron (\( e^- \)) is emitted as a beta particle.
• An antineutrino (\( \bar{\nu}_e \)) is released to conserve lepton number.

Effect on Atomic Number

Since a neutron is converted into a proton, the atomic number (\( Z \)) of the nuclide increases by 1, but the mass number (\( A \)) remains unchanged.

Example of β⁻ Decay

Consider the beta decay of carbon-14:

\[ {}^{14}_6C \rightarrow {}^{14}_7N + e^- + \bar{\nu}_e \]

Here, carbon-14 (\( ^{14}_6C \)) transforms into nitrogen-14 (\( ^{14}_7N \)), increasing its atomic number while keeping the mass number constant.

Conclusion

β⁻ decay is a fundamental nuclear process that allows neutron-rich nuclides to move toward a stable configuration by converting excess neutrons into protons.