A method for determining 231Pa has been studied, through neutron irradiation, separation of protactinium by solvent extraction with di-isobutyl ketone, and γ-ray spectrometry of 232Pa produced by (n, γ) reaction. Preliminary concentration of protactinium before irradiation was carried out by adsorption on quartz powder in polyethylene column. In the γ-ray spectrum, the total counts in the region of 0.781.09 MeV decay with a half life of 232Pa, which can be used as a measure of the relative amount of this nuclide. The total chemical yield was obtained by using the total counts in the region of 0.270.36 MeV in that spectrum, which was attributable to the activity of 233Pa added in the sample in the beginning as tracer. The applicability of this activation method for the determination of 231Pa was confirmed by preparing a calibration curve for some samples containing 10-8 to 10-10 g of 231Pa.
The sensitivity of the present method is discussed with respect to irradiation time and value of the neutron flux, in comparison with the α-ray counting method for this nuclide. Another method using γ-ray counting with discrimination level was examined and found to be also valid for the determination of 232Pa produced in the irradiated sample.