Question

90% of a radioactive sample is left undecayed after time t. What percentage of initial sample will decay in time 2t 1) 20% 2) 19% 3) 40% 4) 38%

Answer 1

Explanation:

N'/N = e^-λt

90/100 = 9/10 = e^-λt -------- 1

㏑9/10 = -λt

N'/N = e^-λ2t = (e^-λt)²

N'/N =  (9/10 )² = 81/100

Percentage of initial sample will decay in time 2t

ie (N' -N )/N = 81/100 -1 =19%