Nuclear Physics – Nuclear fission in fissile materials is caused by the impact of which particle?

Introduction / Context:
Nuclear fission is the process where a heavy nucleus (like U-235 or Pu-239) splits into two lighter nuclei with the release of energy and more neutrons. Understanding which incident particle typically triggers fission is fundamental to reactor physics and nuclear engineering.

Given Data / Assumptions:

• We seek the projectile that most effectively induces fission in fissile isotopes.
• Common candidates: neutron, proton, deuteron, electron.
• Thermal neutrons are especially effective for U-235.

Concept / Approach:
Neutrons have no electric charge, so they can penetrate the Coulomb barrier of a nucleus more readily than charged particles (protons, deuterons). Once absorbed, the compound nucleus becomes unstable and may fission. Electrons interact via electromagnetic processes and do not induce fission in the way neutrons do.

Step-by-Step Solution:
Identify the Coulomb barrier issue for charged particles.Note that neutrons avoid electrostatic repulsion and are readily captured.Recognize that thermal (slow) neutrons are ideal for many fissile isotopes.Select “neutron”.

Verification / Alternative check:
Chain reactions rely on fission neutrons producing further fissions; this feedback would not work with charged projectiles in conventional reactors.

Why Other Options Are Wrong:

• proton: repelled by positive nucleus; inefficient for inducing fission.
• deuteron: also charged; used in other nuclear reactions, not standard fission initiation.
• electron: interacts weakly with nuclei for fission purposes; mainly causes ionization.

Common Pitfalls:
Assuming any subatomic particle can cause fission; in practice, neutrons are uniquely suited for initiating and sustaining chain reactions.

Final Answer:
neutron