Direct activity determination of 54Mn and 65Zn by a non-extrapolation liquid scintillation method.

The measurement of 54Mn and 65Zn by liquid scintillation coincidence counting results in low detection efficiencies. The activity obtained from the extrapolation of efficiency data can therefore become problematic if curvature is present. The simple decay scheme exhibited by these radionuclides, with the emission of an energetic gamma ray, allows the absolute activity to be determined from 4pie-gamma data by direct calculation without the need for efficiency extrapolation. The method, which relies on determining the probability of the gamma-ray interacting with the scintillator solution, is described and validated by measurements made on 60Co.