The importance of the beta spectrum calculation for accurate activity determination of 63Ni by means of liquid scintillation counting

• Nickel-63 was measured by means of two liquid scintillation counting techniques.
• CIEMAT/NIST efficiency tracing and the TDCR method were used.
• Both methods agree provided that an adequate beta spectrum is applied.
• The 63Ni beta spectrum calculation must account for the atomic exchange effect.

The activity concentration of a 63Ni solution was determined by means of two liquid scintillation counting techniques: the TDCR method and the CIEMAT/NIST efficiency tracing technique. The results of both methods are in excellent agreement, provided that the 63Ni beta spectrum calculation accounts for the atomic exchange effect. Thus, new beta spectrum calculations resolve a discrepancy that has been found in previous analyses. The influence of the computed beta spectrum on the final uncertainty of the activity concentration is discussed.