A new method for secondary standard measurements with the aid of liquid scintillation counting

A new secondary standard measuring procedure based on liquid scintillation counting has been developed at PTB. In this procedure, the efficiency curve, i.e. the counting efficiency of the nuclide to be investigated as a function of the tritium counting efficiency, is—in contrast to the CIEMAT/NIST method—not calculated but determined by experiment. For the measurements, gamma-emitting activity standards are used which were calibrated by other methods. The procedure was successfully used to calibrate solutions of the radionuclides 54Mn, 57Co, 65Zn, 85Sr and 125I with small uncertainties.