Quantitative determination of 252Cf

Sealed 252Cf sources in the microCurie to milliCurie range are routinely used in industry and research. At present, no reliable analytical method is available for precise determination of the activity. Very strong sources can be analyzed by neutron counting but the error is large. We propose to use γ-ray spectroscopy for such analysis. In particular, high-energy γ rays (above 1 MeV) of fission fragments in equilibrium with the source are very convenient because they have little absorption in materials surrounding the source. It is found that the 1435.8-keV γ-ray of 138Cs and the 1596.5-keV γ-ray of 140La are well isolated and sufficiently above the background under these peaks. We have measured the γ/α ratio for the 252Cf with an uncertainty of better than 5%. The experiment involved the preparation of several thin 252Cf sources, alpha pulse height analysis, determination of α decay rate, and the measurement of γ singles spectrum with a well-shielded germanium spectrometer. The measured ratio and the γ-ray spectroscopy of unknown samples can provide the activity of 252Cf in these samples.