A radioactive substance has a half life of 20 days. What fraction of the original radioactive nuclei will remain after 80 days?
- \( \frac{1}{32} \)
-
\( \frac{1}{16} \)
- \( \frac{1}{8} \)
- \( \frac{1}{4} \)
The correct answer is: B
Explanation
80 days = 4 half lives (i.e 4 x 20dqs = 80dq)
But the fraction always left by any radioactive material after 4 half lives is
\( \left ( \frac{1}{2} \right)^4 = \frac{1}{16} \)