radioactivity and nuclear exam style q's

Question 1

A thermal nuclear reactor produces radioactive waste.
State the source of this waste and discuss some of the problems faced in dealing with the waste at various stages of its treatment.
Your answer should include:
• the main source of the most dangerous waste
• a brief outline of how waste is treated
• problems faced in dealing with the waste, with suggestions for overcoming
these problems. (6)

Answer 1

• most dangerous waste is material from spent fuel rods, for example uranium and products of fission
• place in ponds of water to cool for a long time
• ideally, uranium is separated and recycled
• waste is vitrified (encased in glass, which is non-porous so it doesn’t enter water supplies)
• store deep underground, radiation risk to organisms is minimal
• placed in steel barrels
• can stay radioactive for hundreds of years, efforts must be made so it is not removed in that time
• handle with robots or long tools, not to touch skin

Question 2

State two possible reasons why results for using a G-M radiation detector to detect the counts from a radioactive source do not follow the expected inverse-square
law.

Answer 2

The random nature of the radiation count (although small in this case)

Dead-time in the G-M detector

d is not the real distance between source and detector or source is not a point source

The source may not be a pure gamma emitter.
(Gamma and beta are acceptable but not gamma and alpha together)

A reference to short half-life provided that an explanation of how this has an effect on separate measurements eg activity changes during the measurements.

Assumes no absorption between source and detector (although small in this case)

Question 3

Explain why the public need not worry that irradiated surgical instruments become
radioactive once sterilised.

Answer 3

because it is gamma radiation, energy of photons is not high enough to induce radiation

Question 4

Calculate the activity of a sample of 87-Rb with a radioactive decay constant of 1.42 × 10^–11 year^–1 of mass 1.23 mg

Give an appropriate unit for your answer.

Answer 4

Question 5

Explain why the metastable form of the isotope of technetium 99Tc is a radioactive source suitable for use in medical diagnosis.

Answer 5

It only emits 𝜸-rays.

𝜸-rays are weakly ionising/cause less damage to body than other radiations.

𝜸-rays can penetrate/escape from the body.

It has low toxicity

Half-life is short enough not to remain in the body for too long after the medical examination.

Half-life is long enough to complete the diagnosis.

It can be prepared in the hospital/close to the hospital.