The Determination of Isotopic Ratio of ²³⁵U/²³⁸U by Neutron Activation

Abstract

The isotopic ratio of ²³⁵U/²³⁸U is determined according to the technique of neutron activation analysis without any tedious chemical separation. Although several works had been carried out along this line, the irradiation of uranium sample was limited to some particular conditions because of high fission cross section value for ²³⁵U.
In the present methods, 100 mg of uranium oxide-oxalic acid mixture (1: 8000) is irradiated in JRR-1 for 1 hr. After about one day cooling, the γ-activity of the sample is studied spectrometrically.
The dilution of uranium sample with a large amount of oxalic acid gives various advantages in slowing down fast neutrons, in capturing recoil fission products or in taking very small amount of uranium for irradiation.
Two methods are proposed and compared each other. The first method is based on the relative ratio between activities in the energy region containing γ-activity due to ²³⁹Np and those in the higher energy region free from the activity of ²³⁹Np. In the second method, the strength of γ-activity due to fission produtcts is measured as the amount related closely to the ²³⁵U concentration.