JEE Advanced2017PhysicsNuclear PhysicsActual
  131 I   i s an isotope of Iodine that β   decays to an isotope of Xenon with a half-life of 8   d a y s . A small amount of a serum labelled with   131 I is injected into the blood of a person. The activity of the amount of   131 I injected was 2.4 × 10 5 Becquerel (Bq). It is known that the injected serum will get distributed uniformly in the blood stream in less than half a
Correct answer
5
Step-by-step solution
t 1 2 = 8 d a y s A = A 0 e - λ t e λ t 115 = A 0 A 0 = 115 1 + λ t = 115 1 + l n 2 t 1 2 × 11.5 A 0 = 115 × 1.042 = 119.82 A 0 ≅ 120 B q 120 Bq is the activity of 2.5 ml ∴ 2.4 × 10 5 B q is the activity of 2.5 × 10 - 3 120 × 2.4 × 10 5 ∴ Total volume of blood = 5 litres