[en] The cross sections for the reaction ⁶⁵Cu(n,2n)⁶⁴Cu were measured at 13.692, 14,473 and 14,822 MeV using the activation technique, with an accuracy of 1.4-1.5%, relative to well-known cross sections for the reference reaction ²⁷Al(n,α)²⁴Na. The reaction T(d,n)⁴He was used to produce the neutrons. Activity measurements were performed with a 12.7 x 12.7 cm NaI(Tl) well-type detector using a recently measured value for the β⁺-branching ratios of ⁶⁴Cu. The new cross-section values were incorporated in a reevaluation of the ⁶⁵cu(n,2n)⁶⁴Cu cross section simultaneously with some other important cross sections at 14.70 MeV yielding a consistent set with uncertainties (1 σ) of 0.6-2.0%. The uncertainty for the evaluated ⁶⁵Cu(n,2n)⁶⁴Cu cross section could be reduced to 1.2%. (author)