A certain radioactive isotope placed near a Geiger counter registers 160 counts per second. Eight hours later, the counter registers 10 counts per second. What is the half life of the isotope?
A) 4 hours
B) 6 hours
C) 8 hours
D) 2 hours
E) none of these

Question

Quizplus · Accepted Answer

The half-life can be calculated using the formula for exponential decay, where the number of counts decreases by half for each half-life period. From 160 counts to 10 counts, the isotope halves its activity 4 times (160 to 80 to 40 to 20 to 10), which occurs over 8 hours. Therefore, each halving takes 2 hours, making the half-life 2 hours.

A Certain Radioactive Isotope Placed near a Geiger Counter Registers