Phyl is in hospital. She is injected with the radioisotope technetium-99m.

This isotope is absorbed by the thyroid gland in her throat. A radiation detector placed outside her body and above her throat detects the radiation. Technetium-99m has a half-life of 6 hours. It emits gamma radiation.

a. Why is an emitter of alpha radiation unsuitable?

b. i. How long will it take for the activity of the technetium-99m to fall to a quarter of its original value?

ii. After 24 hours, how will the activity of the technetium-99m compare with its original value?

c. Eventually the level of radiation from the technetium-99m will fall to less than the level of the background radiation. State two naturally occurring sources of background radiation.