= Shell-model prediction for yttrium-91 beta decay
Using the orbital order after 28 supplied in the simple shell model, <proton> counts 32 and 38 fill $2p_{3/2}$ and $1f_{5/2}$, so the odd 39th <proton> occupies $2p_{1/2}$. With paired valence <neutrons> this gives a $1/2^-$ yttrium-91 ground-state prediction. The daughter has paired 40 <protons> and one <neutron> beyond the 50-neutron closure in $2d_{5/2}$, giving $5/2^+$. The inferred ground-state beta transition is therefore first-forbidden unique. This is a stated paired-shell model deduction; an endpoint diagram alone does not determine the <spin> assignment or an evaluated <isotope> <mass>.
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