Practice portal › Nuclei › Composition and Size of the Nucleus
Asked in GUJCET 2021 · Composition, isotopes and isobars
Idea: every proton repels every other proton, whatever the distance, while the attractive nuclear force reaches only as far as the next nucleon. Extra neutrons add attraction without adding repulsion, so heavy stable nuclei are neutron-rich.
Check the stable heavy nuclides: ²⁰⁶₈₂Pb has N/Z=124/82≈1.5; ²³⁸₉₂U has 146/92≈1.6.
So the neutron-to-proton ratio needed is about 1.5, that is 3:2.
(For light nuclei the same ratio is close to 1:1.)
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