Someone argues: "A rotating rigid body carries the full rigid-body moment of inertia…

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

The Nucleus Resolved, Ch Collective motion: the deformed nucleus, vibrations, rotations and giant resonances

Problem

Someone argues: "A rotating rigid body carries the full rigid-body moment of inertia

\mathcal I_{\rm rigid}

because every part of it is locked to every other part. Pairing locks nucleons together into strongly correlated

J=0

pairs, an even tighter binding than an ordinary rigid solid. So pairing ought to push the measured

\mathcal I

of a rotating deformed nucleus above

\mathcal I_{\rm rigid}

, not below it; the measured values with

\mathcal I<\mathcal I_{\rm rigid}

(for example

\mathcal I\approx0.53\,\mathcal I_{\rm rigid}

in the

^{238}\mathrm U

ground band) must have some cause other than pairing." ((a)) Find the error in this argument. ((b)) Give the correct qualitative reason pairing lowers the measured

\mathcal I

below

\mathcal I_{\rm rigid}

, and say what backbending at high spin shows about this mechanism.

Related theory

Nuclear Physics

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