A certain radioactive isotope placed near a Geiger counter registers 120 counts per minute. If the half-life of the isotope is one day, what will be the count rate at the end of four days?
A)30 counts/min
B)15 counts/min
C)10 counts/min
D)7.5 counts/min
E)5 counts/min

Question

Quizplus · Accepted Answer

The count rate decreases by half every day due to the half-life of the isotope. After four days, the count rate would be halved four times: 120 counts/min → 60 (after 1 day) → 30 (after 2 days) → 15 (after 3 days) → 7.5 counts/min (after 4 days).

A Certain Radioactive Isotope Placed near a Geiger Counter Registers