Which process requires extremely high temperatures to force nuclei together?

• A. Fission
• B. Fusion
• C. Radiative capture
• D. Spontaneous decay

Answer: (B)

Overcoming the electrostatic repulsion between positively charged nuclei to fuse requires extremely high temperatures to provide the necessary kinetic energy. For fusion, light nuclei must get close enough for the strong nuclear force to act, which happens more readily when particles move extremely fast. This is why stars have core temperatures of millions of kelvin, and why achieving fusion on Earth demands creating and confining a hot, dense plasma at tens of millions of kelvin. The other processes don’t rely on such heat input: fission can be initiated by absorbing a neutron and splitting a heavy nucleus, radiative capture involves a nucleus taking in a neutron and emitting a gamma ray (driven by neutron availability rather than heat), and spontaneous decay occurs without external energy input, governed by nuclear stability.