Application of radio-analytical technique for determination of “Age” of nuclear materials for nuclear forensics

Abstract

Determination of “Age” – the time elapsed since the last chemical purification – of a nuclear material is an important parameter in Nuclear Forensic analysis. Estimation of age may give crucial acumen of the possible production facility and the declared origin – if available – in case of a suspected nuclear material which is out of regulatory control. Mass spectrometry is the most common analytical technique used for chronological studies due to its superior precision (lower uncertainty). Though alpha spectrometry can be used for age determination, it better suits for irradiated fuel based radio-chronology because of higher specific activity of irradiated actinides (actinides formed by irradiation of actinides within a reactor) like plutonium. This paper describes the application of alpha spectrometry for the age determination in some natural U-metal samples with known history. The method utilises the radioactive non-equilibrium existing between 234U and 230Th isotopes in the sample for the elucidation of age of the material. Optimisation of a chemical procedure for the separation of ultra-trace amount of thorium isotopes from bulk uranium material using double column anion exchange chromatography is also presented. The chemical recoveries of uranium and thorium obtained with the present method were >95%. The uncertainty in age determination was <10% and ∼15% for older (∼51 years) and newer (∼11 years) samples respectively. The method is also used to elucidate the age of an unknown uranium material and found to be 39 ± 4 years old.

Keywords

• Uranium age
• 234U-230Th radiochronometer
• Nuclear forensics
• Ion exchange chromatography
• Alpha spectrometry