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
75,000 particles
35,000 particles
25,000 particles
50,000 particles
Correct answer is C
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.