Radioactivity and Particles
5 marks · NormalA student investigates the penetration of different types of radiation in a laboratory experiment and learns how radioactive substances can be detected.
Name one instrument that can detect ionising radiation and briefly describe how it works.
The student places a piece of aluminium between a radioactive source and a Geiger-Müller tube. The count rate drops to background level. Explain what this tells you about the type of radiation being emitted and why.
State one unit you would use to record the activity in this investigation.
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(a) Geiger-Müller tube; it detects radiation when ionising particles cause gas inside the tube to conduct electricity, resulting in a current that is measured.
(b) The radiation is likely to be beta because aluminium can stop beta particles but not gamma rays. Since the count drops to background level, the radiation cannot be gamma, which would require lead to stop it.
(c) becquerel (Bq)
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Marking points
B1 (a) · 1 mark · Names a valid detector, e.g., Geiger-Müller tube or photographic film.
M1 (a) · 1 mark · Gives a brief description of how the detector works.
M2 (b) · 1 mark · Explains why aluminium stops beta but not gamma; identifies the type as beta.
E1 (b) · 1 mark · Correctly excludes gamma radiation by reasoning.
B2 (c) · 1 mark · Becquerel (Bq) is correctly stated as the activity unit.
Worked solution
a) One suitable instrument is the Geiger-Müller tube. It detects ionising radiation because radiation entering the tube ionises the gas inside, allowing a current to flow, which is counted electronically.
b) Aluminium stops beta particles. Since the count rate drops to background level after placing aluminium, the source must be emitting beta radiation. Gamma radiation would require thick lead to stop it.
c) The activity is measured in becquerels (Bq).