What is a typical consequence when a nucleus captures a slow neutron?

• A. It becomes more stable.
• B. It emits a proton.
• C. It becomes unstable or radioactive.
• D. It immediately decays to a stable isotope.

Answer: (C)

When a nucleus captures a slow (thermal) neutron, it gains one neutron, forming a heavier isotope. This new nucleus is often left in an excited state and will typically release energy or gamma rays to settle, but the added neutron commonly makes the isotope unstable. It will usually undergo radioactive decay (such as beta decay) to move toward a more stable configuration. So the typical consequence is that the nucleus becomes unstable or radioactive.

Emitting a proton isn’t the usual immediate outcome of simply capturing a neutron, and the nucleus does not automatically decay to a stable isotope right away—the decay to stability generally occurs over time through subsequent radioactive processes.