Question

The atomic ratio between the uranium isotopes ²³⁸U and ²³⁴U in a mineral sample is found to be 1.8 × 10⁴. The half life of ²³⁴U isT_1/2(234) = 2.5 × 10⁵ years. The half-life of ²³⁸U is –

• A. 4.5 × 10⁹years
• B. 5.4 × 10⁹years
• C. 4.5 years
• D. 5.4 years

Answer 1

Answer: (A)

4.5 × 10⁹years

Answer 2

In radioactive equilibrium

l₁N₁ = l₂N₂

=

T₂ = × T₁

T₂ = 1.8 × 10⁴ × 2.5 × 10⁵

T₂ = 4.5 × 10⁹ years