Thorium estimation in uranium bearing materials and application in age determination

Estimation of isotopes of Th, and U was carried out in some uranium samples like uranium metal and uranium ore. ²³⁰Th, the immediate daughter of ²³⁴U in natural uranium series, is an important candidate used for estimating the age of a uranium sample. It is commonly known as U-Th chronometry, upto 1 million years, if they are not in radioactive equilibrium. The extent to which the secular equilibrium reached between ²³⁰Th and ²³⁴U, may be found out by measuring the activities of the isotopes. ²³⁰Th has a higher specific activity compared to ²³²Th, hence radiometric technique based on alpha detection is superior compared with mass determination for quantification of ²³⁰Th, whereas for determination of ²³²Th, mass spectrometry is preferred. The study shows that the activities of ²³⁸U in ore sample calculated from ^234mPa from gamma spectrometry and ²³⁰Th from alpha spectrometry are in radioactive equilibrium and the age of the ore is greater than 1 million years. The activity ratio of ²³⁰Th to ²³⁴U obtained from alpha spectrometry in uranium metal is 0.00063±0.00016. Since the studied metal is depleted uranium, age determination from the activity ratio cannot be applied. However radio-chronology can be applied for age determination of natural uranium metal and uranium ore concentrate (studies are in progress) if the isotopes of Uranium and Thorium are not in radioactive equilibrium