MEASUREMENT OF 113mCd IN IRRADIATED CADMIUM SHIELDING USING LIQUID SCINTILLATION COUNTING

ABSTRACT. The ongoing program of nuclear facilities decommissioning within the UK has generated a requirement for the characterization of diverse waste forms. Many of the radionuclides requiring quantification are rarely encountered in routine radioanalytical studies. One such radionuclide is 113mCd, which is produced via neutron activation of Cd in reactor control rods and shielding. The nuclide decays predominantly via beta emission (Eβmax = 580 keV; 99.86%), which is accompanied by gamma emission with very low yields (Eγ = 263.7 keV; Iγ = 0.02296%). Quantification of 113mCd in decommissioning wastes by gamma spectrometry is therefore mostly limited to high-activity samples. Liquid scintillation counting offers an attractive alternative for sensitive measurement of this nuclide but is restricted by the lack of any reference standard suitable for instrument calibration. Calibration using the Ciemat-NIST approach has therefore been evaluated. 113mCd was purified using a validated separation procedure from irradiated Cd obtained from a UK research reactor. The purified fractions were then measured on a Wallac 1220 Quantulus liquid scintillation counter previously calibrated using the Ciemat-NIST (CN) approach and results compared with those obtained by gamma spectrometry. Good agreement was observed, confirming the suitability of liquid scintillation counting for the quantification of 113mCd and the validity of using the CN calibration method for radionuclides where no reference standards are currently available