Solutions: Radioactivity Questions
Q18.
(a) Which of the following forms of ionizing radiation produces the greatest number of ion pairs per mm in air? (Tick the correct answer)
α particles
|
|
β particles |
|
γ rays |
|
X-rays |
|
[1 mark]
(b)
(i) Complete the table below showing the typical maximum range in air for α and β particles.
Radiation Type |
Typical maximum range in air /m |
α |
0.06 |
β |
1 |
For alpha particles the examiners allowed 0.03 m to 0.07 m
For beta particles they allowed 0.20 m to 3.0 m
[2 marks]
(ii) γ rays have a range of at least 1 km in air.
However, a γ ray detector placed 0.5 m from a γ ray source detects a noticeably smaller count-rate as it is moved a few centimetres further away from the source.
Explain this observation.
The gamma rays spread out radially from the source.
Therefore the intensity of radiation decreses with the square of the distance from the source - it follows the inverse square law. This means that the further away from the source the detector is placed the lower the intendity of radiation it will register - doubling the distance will reduce the intensity to a quarter of the value - tripling it will reduce the intensity to a ninth etc..
[1 mark]
(c) Following an accident, a room is contaminated with dust containing americium (which is an α-emitter). Explain the most hazardous aspect of the presence of this dust to an unprotected human entering the room.
The dust may be ingested (or 'taken into the body' or 'breathed in') causing molecules in human tissue (or cells) to be mutated (or made cancerous or killed or damaged) by ionisation
[2 marks]
(Total 6 marks)