PHYSICS · Single correct · A Level · Physics · Particles and radiation · Particles and radiation
Problem
In some light nuclei, adding a single neutron transforms an unstable nuclide into a stable one. Which explanation best accounts for this observation?
(a) The neutron shields the protons from each other's electric field, effectively lowering the Coulomb repulsion and stabilizing the nucleus.
(b) When the neutron is absorbed, one of the protons is changed into a neutron, so the proton count drops and electrostatic repulsion decreases.
(c) Because the strong nuclear force is short-ranged and saturates, the extra neutron can make additional strong-force links with neighboring nucleons, increasing the overall binding energy.
(d) Adding a neutron allows different nucleons to swap quantum states, letting protons fall into lower-energy levels through the Pauli exclusion principle and therefore increasing stability.