Someone argues: "The giant dipole resonance in has

PHYSICS · Multi-part · Fermi University Physics · Nuclear Physics · The nuclear force and nuclear models · Nuclear reactions

The Nucleus Resolved, Ch Reaction mechanisms: resonances, the compound nucleus, direct reactions and the optical model

Problem

Someone argues: "The giant dipole resonance in 90Zr^{90}\mathrm{Zr} has Γ=5.0 MeV\Gamma = 5.0\,\mathrm{MeV}. Since Γ=ℏ/τ\Gamma = \hbar/\tau sets the total decay rate, and decay of an excited nucleus must mean a nucleon leaves it, all 5.0 MeV5.0\,\mathrm{MeV} of width must be direct-nucleon escape width Γ↑\Gamma^\uparrow." A single-particle (direct-emission) calculation of the escape width for this doorway state gives Γ↑=0.6 MeV\Gamma^\uparrow = 0.6\,\mathrm{MeV}. ((a)) Find the spreading width Γ↓\Gamma^\downarrow implied by Γ=Γ↑+Γ↓\Gamma = \Gamma^\uparrow + \Gamma^\downarrow. ((b)) State which decay mode dominates and, in one or two sentences, what it represents physically. ((c)) Explain what is wrong with the claim in the argument above.

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