Part 1. Strontium90 is one of the products of the fission of uranium235. This st

Question

Part 1. Strontium90 is one of the products of the fission of uranium235. This strontium isotope is radioactive, with a half-life of 28.1 yr. Calculate how long (in yr) it will take for 2.50 g of the isotope to be reduced to 0.600 g by decay.

Part 2. Tritium, 3H, is radioactive, decaying by electron emission with a half-life of 12.5 years. In ordinary water, the ratio of 1H to 3H is 1.0 × 1017 to 1. How many disintegrations will be observed per minute in a 4.50kg sample of water? (Answer: ~disintegrates/min)

Explanation / Answer

half life = 28.1 yrs

decay constant = k = 0.693 / t1/2

k = 0.693 / 28.1

k = 0.0245 yrs

initial = Ao = 2.50 g

remaining = At = 0.600 g

radioactive decay follows first order kinetics

t = 1/k * ln (Ao / At)

t = 1/ 0.0245 * ln (2.50 / 0.600)

t = 58.24 years

time taken = 58.24 years

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