Answer:
54 days
Explanation:
The half-life is the time need for the mass decrease by half. Thus, if the initial mass is m, after one half-live it will be m/2. Then, if another half-live pass, the m/2 mass will decrease by half, being m/4, and then successfully. After n half-lives, the final mass (M) is:
M = m/2ⁿ
So, if the final mass is 8μCi, and the initial is 32:
8 = 32/2ⁿ
2ⁿ = 32/8
2ⁿ = 4
n = 2
So, it's necessary to pass 2 half-lives, or 54 days to the mass decrease to 8μCi, thus after 54 days it will be less than 8μCi.
