A radioactive nucleus has a half-life of 20 years, starting with 100,000 particles, how many particles will be left exactly at the end of 40 years
-
A.
75,000 particles -
B.
35,000 particles -
C.
25,000 particles -
D.
50,000 particles
Correct Answer: Option C
Explanation
Given:
t(_{frac{1}{2}) = 20 years
After the first 20 years, half of the substance ((frac{1}{2} times 100,000 = 50,000)) will have decayed. Hence, we have 100,000 – 50,000 = 50,000 particles left.
After the second 20 years (being 40 years in all), half of the remaining substance ((frac{1}{2} times 50,000 = 25,000)) will have decayed.
Remaining particles after 40 years = 50,000 – 25,000
= 25,000 particles.
There is an explanation video available below.