  A simple model based on the group SO(5) suggests that both the like-particle
and neutron-proton components of isovector pairing correlations in odd-A nuclei
are Pauli blocked. The same effect emerges from Monte Carlo Shell-model
calculations of proton-rich nuclei in the full fp shell. There are small
differences between the two models in their representation of the effects of an
odd nucleon on the competition between like-particle and neutron-proton
pairing, but they can be understood and reduced by using a two-level version of
the SO(5) model. On the other hand, in odd-odd nuclei with N not equal to Z
SO(5) disagrees more severely with the shell model because it incorrectly
predicts ground-state isospins. The shell model calculations for any fp-shell
nuclei can be extended to finite temperature, where they show a decrease in
blocking.
