I keep getting “Nuclear size and density” questions wrong in Nuclei. What's the trap?
thinking a nucleus with twice the nucleons has twice the radius.
The usual trap: thinking a nucleus with twice the nucleons has twice the radius. How to avoid it: mass number grows with volume, so radius grows by the cube root. Go back to the definition — Nuclear radius scales as R = R_0 A^(1/3), so volume scales with nucleon number A. Because mass also scales with A, nuclear density is approximately constant across nuclei.
Key point
Nuclear size and density
Common mistake
thinking a nucleus with twice the nucleons has twice the radius.
Memory tip
mass number grows with volume, so radius grows by the cube root.
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