  Calculations of nuclear spin-lattice relaxation rates are carried out by
means of exact diagonalization on small (2 x 6) antiferromagnetic Heisenberg
ladders, using the simplest forms permitted by symmetry for the hyperfine
couplings for the three nuclear sites in Cu2O3 ladders. Several values of the
rung/chain exchange ratio have been considered. Comparisons with experimental
results, field theoretic calculations, and the Gaussian approximation highlight
some open problems.
