Cu nuclear magnetic relaxation rate 1/T1 has been measured in the antiferromagnetic heavy-electron compound UCu5 (TN=15k) in the paramagnetic state under zero external field by NQR technique. At high temperatures 1/T1 tends toward a constant, whereas on approaching TN it shows marked critical divergence, which has been found close to T1T∝ (T-TN)0·4. An analysis has been made in terms of an exchange-coupled Kondo-impurity model, and the divergent behavior has been shown to be not incompatible with the model. At high temperatures, neglecting the q-dependences in [formula omitted](q, ω) and taking account of the neutron quasielastic linewidth at 50 K, the relaxation rate of U moments has been deduced. The large relaxation rate and its strong temperature-dependence suggest both the strong hybridization between 5f and conduction electrons and the dominance of the single-site dynamics in the U moment relaxation in UCu5.
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