Radioactivity (Extended Response)

Question 1

Some types of cancer can be treated by using a radioactive material from inside the body, whereas other cancers are treated by using a radioactive source outside the body

Explain how cancer can be treated in both cases

Your answer should refer to examples of suitable isotopes, the radiation emitted and the half life of these isotopes [6]

Answer 1

• internal radiation therapy involves:
• brachytherapy - placing of seeds, ribbon or capsules close to the tumour inside the body
• injection or consumption of a radioisotope that travels through the body and kills/locates cancer cells
• the half life is low for internal materials - hours/days/weeks
• iodine-131, beta emitter, treats thyroid cancer, half life of 8 days
• alpha emitters are also used as they only need to travel short distances
• the half life needs to be long enough to treat the cancer without causing long term harm to the patient
• weak gamma rays are fired from different positions around the body when treating externally
• they focus on the cancer tumour but don’t damage healthy cells too much
• come from an external source with a long half life to avoid frequent replacement
• cobalt-60, half life of 5 to 6 years

Question 2

Radioactive material is used in smoke alarms. Explain the characteristics of the radioactive material used in smoke alarms. Your answer should refer to suitable and unsuitable radioactive materials for this purpose [6]

Answer 2

• alpha source must be used
• alpha particles ionise the air leading to the production of electrons and ions and allowing a current to flow
• alpha particles cannot reach the body because they are stopped by a few cms of air so don’t present a risk to people in the room
• beta particles and gamma rays are much more penetrating and can reach the body, and so would present a risk to nearby people
• beta and gamma are dangerous if they reach the body, as they can damage cells causing them to mutate, which could lead to cancer