Impurity effect on nuclear magnetic relaxation due to orbital hyperfine interaction

We show that the nuclear magnetic relaxation rate $1/T_1$ due to the coupling of nuclear spin to the orbital moment of itinerant electrons is sensitive to impurity scattering in both normal and superconducting states. In the clean case $1/T_1$ diverges because of the contribution from distant currents, while in the dirty case its magnitude is controlled by the parameter $k_F l$, where $l$ is the electron mean free path. In the superconducting state temperature dependence of $1/T_1$ becomes significant.