[en] A ⁶⁴Cu solution was standardized by means of liquid scintillation counting. The activity of the solution was also determined with an ionization chamber whose response was simulated by using a Monte Carlo code. The photon emission intensities including K X-rays were determined to be I₅₁₁=35.1 (3)%; I₁₃₄₆=0.472 (12)%, IKα=14.41 (15)%, IKβ=2.01 (3)%, respectively. ⁶⁴Cu half-life was also determined as 12.718 (23) h. The new decay scheme used in the present work was established following the EURAMET 1085 exercise where a good agreement between activity measurement techniques was found.