Radioactivity and Particles
5 marks · NormalA scientist uses a Geiger-Muller tube to investigate a radioactive isotope in the laboratory. The isotope decays by emitting beta particles. The scientist also uses a stopwatch to record results.
State the unit used to measure the activity of the radioactive isotope.
Explain how the Geiger-Muller tube detects ionising radiation.
Describe what happens to the atomic number and mass number of the isotope after each beta decay.
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(a) becquerel (Bq)
(b) The GM tube contains gas that gets ionised when radiation enters. The ions allow a current to flow, which gets counted as a click or signal.
(c) The atomic number increases by 1 and the mass number stays the same after each beta decay.
Common mistakes: Confusing units (e.g. using 'curie' or 'counts per minute'); Vague answers for GM tube (not mentioning ionisation inside tube); Incorrectly stating both mass and atomic numbers change by 1
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Marking points
B1 (a) · 1 mark · State 'becquerel' (Bq) as the unit.
B1 (b) · 1 mark · Mentions ionisation or ions are created inside the GM tube.
B1 (b) · 1 mark · Notes ions allow current to flow leading to signal/click/count.
B1 (c) · 1 mark · Atomic number increases by 1.
B1 (c) · 1 mark · Mass number stays the same.
Worked solution
a) The activity of a radioactive isotope is measured in becquerels (Bq).
b) The Geiger-Muller tube has a gas inside. When ionising radiation enters the tube, it ionises the gas, producing ions which allow a small current to flow. This pulse is detected electronically and counted.
c) When a nucleus undergoes beta decay, a neutron changes into a proton and an electron. The atomic number (number of protons) increases by 1, but the number of nucleons stays the same, so the mass number stays the same.