Based on the radioactive decay model:
A = A₀exp(-kt) ----(1)
where
A = concentration of the radioisotope at time t
A₀ = initial concentration
k = decay constant
t = time
Now, based on the given data:
A₀ of I-125 = 0.8 g
Since the decay rate is 1.15% per day, the amount of I-125 left after t = 1 day is: A = 0.8 - (1.15/100)*0.8 g = 0.7908 g
substituting for A, A₀ and t in eq(1) we get:
0.7908 = 0.8 exp(-k*1)
k = 0.01157 day-1
The decay constant is related to t1/2 as follows:
t1/2 = 0.693/k
= 0.693/0.01157 = 59.89 days
Ans: The t1/2 for I-125 approximately 60 days
