Uses of Radioisotopes

Question 1

Where does background radiation come from?

Answer 1

• Radioactive substances present in rocks and soil, especially granite
• Cosmic rays from space
• Man-made sources such as radioactive waste from industry and hospitals

Question 2

How do we use tracers in underground pipes?

Answer 2

• Small amount of gamma emitter is put into the pipe
• Detector is passed along the ground above the path of the pipe
• An increase of activity is detected above the region of the leak and little or no radiation is detected after this point
• Gamma radiation is used because it can penetrate to the surface

Question 3

How do smoke detectors work?

Answer 3

• Contains isotope which emits alpha radiation
• Alpha particles ionise in the air without smoke which creates a small current that is detected by the circuit in the smoke alarm
• With smoke in the air less ionisation occurs because the alpha particles are partially blocked and the change in current causes the alarm to sound

Question 4

How does radioactive dating work?

Answer 4

• Some rocks such as granite contain traces of uranium
• The uranium isotope undergoes a series of decays until it forms a stable isotope of lead
• By comparing the amount of uranium and lead present in rock its approximate age can be found
• Uranium has a half life of 4,500 million years so if there is equal amounts of rock and uranium present then the rock is 4,500 million years old

Question 5

How do we use carbon dating?

Answer 5

• Carbon-14 is a radioactive carbon isotope that is present in all living things
• Carbon dating can only be used on things that were once alive
• When something dies it produces no more carbon-14
• As the carbon-14 decays, the activity of the sample decreases
• The ratio of current activity from living matter to the sample activity provides reasonably accurate data