Precision and accuracy in the determination of sup(238)Pu/(sup(239)Pu + sup(240)Pu) alpha activity ratio by alpha spectrometry

Investigations were carried out for the evaluation of precision and accuracy in determining sup(238)Pu/(sup(239)Pu + sup(240)Pu) activity ratio by α spectrometry from the point of view of determining sup(238)Pu accurately in plutonium samples and in exploiting Isotope Dilution Alpha Spectrometry (IDAS) for determining the concentration of plutonium in the irradiated fuel dissolver solutions. Synthetic mixtures with α activity ratios ranging from 0.01 to 10 were prepared using sup(238)Pu and sup(239)Pu isotopes. Different methods which can be routinely used were tried to calculate the α activity ratio from the α spectrum taken on electrodeposited sources prepared from these mixtures. An accuracy of better than 0.5% and a precision of +- 0.2% (1 sigma) is demonstrated in the determination of α activity ratios ranging from 0.01 to 10 using electrodeposited sources and the evaluation method based on the geometric progression decrease (G.P.) for the far tail of the spectrum. (auth.)