Question

Krypton-85 has a half-life of 10.76 years. How many years will it take for a sample of krypton-85 to decay to 30 percent of its initial quantity?

Answer 1

Answer: 5.5 years

Explanation:

Half life, T = 0.693/ decay constant

⇒ decay constant = 0.693/10.76 = 6.4405 × 10^(-2)

Now, ㏑(0.7) = - 6.4405 × 10^(-2) × t

⇒t = ㏑(0.7)/(-6.4405 × 10^(-2))

⇒t = 5.53 y