The time it takes for the number of nuclei of a sample of radioactive isotopes to decrease by half
The diagram shows how the activity of a radioactive sample changes over time. Each time the original activity halves, another half-life has passed
The radioisotope technetium is used extensively in medicine. The graph below shows how the activity of a sample varies with time.Determine the half-life of this material.
Step 1: Draw lines on the graph to determine the time it takes for technetium to drop to half of its original activity
Step 2: Read the half-life from the graph
A particular radioactive sample contains 2 million un-decayed atoms. After a year, there is only 500 000 atoms left un-decayed.What is the half-life of this material?
Step 1: Calculate how many times the number of un-decayed atoms has halved
Step 2: Divide the time period by the number of half-lives