Nickel (Ni) Nucleus Stability Explained

The stability of an atomic nucleus is primarily determined by how strongly its constituent nucleons (protons and neutrons) are held together. This is quantified by the binding energy.

Binding Energy vs. Binding Energy Per Nucleon

While total binding energy represents the energy required to separate all nucleons, it generally increases with the size of the nucleus. A larger nucleus requires more energy overall to break apart.

However, the measure that truly indicates how tightly bound a nucleus is, relative to its size, is the binding energy per nucleon. This represents the average energy required to remove a single nucleon from the nucleus.

Why Ni is Most Tightly Bound

• The binding energy curve, which plots binding energy per nucleon against mass number, peaks in the region of Iron (Fe) and Nickel (Ni).
• This peak indicates that nuclei around Fe and Ni require the most energy per nucleon to be removed.
• Therefore, Ni has the most tightly bound nucleus because it possesses the highest binding energy per nucleon.

Evaluating Other Options

• Highest binding energy: Larger nuclei have higher total binding energy, but aren't necessarily the most tightly bound per nucleon.
• Does not undergo radioactive decay: While Ni isotopes are stable, stability is a consequence of tight binding, not the primary definition of it. Other factors contribute to decay.
• Has a long half-life: A long half-life implies slow decay and relative stability, but binding energy per nucleon is the direct physical measure of how tightly bound the nucleus is.

The key factor defining how tightly bound a nucleus is, is the energy required to remove, on average, one of its constituent particles, which is the binding energy per nucleon.