Question

A Geiger counter registers a count rate of 7,600 counts per minute from a sample of a radioisotope. Eighteen minutes later, the count rate is 1,900 counts per minute. What is the half-life of the radioisotope?

Answer 1

9 minutes is the half life of the radioisotope.

Explanation:

Given;

initial count rate = 7,600 counts per minute

final count rate = 1,900 counts per minute

elapsed time, t = 18 minutes

The half life of the radioisotope is calculated as;

Time (half life) --------------------------remaining count rate

0 ------------------------------7,600 counts per minute

x ------------------------------3,800 counts per minute

2x----------------------------- 1,900 counts per minute

thus, 2x = 18 minutes

x = 18 / 2

x = 9 minutes

Therefore, 9 minutes is the half life of the radioisotope.