A radioactive material with half life of 6.25 years undergoes beta decay. How much fraction of material is decayed after 25 years:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( 15/16 \)
After each half-life the amount of radioactive material halves, so after \( n \) half-lives the amount left is \( N = N_0/2^{n} \).
\( \displaystyle n = \frac{25}{6.25} = 4 \)
\( \displaystyle \frac{N}{N_0} = \frac{1}{2^{4}} = \frac{1}{16} \)
The fraction that has decayed is what is left out of the whole:
\( \displaystyle 1 - \frac{1}{16} = \frac{15}{16} \)