4.3 Alpha, beta and gamma radiation
9 exam questions worth 19 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Which type of radiation is the most strongly ionising?
Choose one answer.
Correct Not quite: the answer is Alpha
Mark scheme
A: Alpha
Model answer
Alpha (A). Alpha particles lose their energy quickly by ionising many atoms.
Which of these is stopped by a sheet of paper?
Choose one answer.
Correct Not quite: the answer is Alpha particles
Mark scheme
A: Alpha particles
Model answer
Alpha particles (A).
State what is meant by the activity of a radioactive source and give its unit.
Mark scheme
the rate at which a source decays / number of nuclei that decay each second (1); becquerel / Bq (1)
Model answer
Activity is the rate at which a source of unstable nuclei decays. It is measured in becquerels (Bq).
A radioactive source gives 4500 decays in 90 seconds. Calculate its activity in becquerels.
Mark scheme
activity = decays ÷ time = 4500 ÷ 90 (1); 50 Bq (1)
Model answer
Activity = 4500 ÷ 90 = 50 Bq.
Describe what an alpha particle and a beta particle are made of.
Mark scheme
alpha: two protons and two neutrons / a helium nucleus (1); beta: a fast-moving electron (from the nucleus) (1)
Model answer
An alpha particle is two protons and two neutrons, the same as a helium nucleus. A beta particle is a high-speed electron emitted from the nucleus.
A student investigates a radioactive source using a radiation detector. When a sheet of paper is placed between the source and the detector, the count rate drops from 400 to 100 counts per minute. When a few millimetres of aluminium is added as well, it drops to 98. Identify the types of radiation the source emits. Explain your answer.
Mark scheme
the paper stopped most of the count so alpha is emitted (1); the aluminium did not reduce the count much so the remaining radiation is not beta (1); the remaining count of about 100 / 98 is gamma (1); background radiation could explain the 98 / the remaining counts are (mostly) gamma (1)
Model answer
The paper reduced the count a lot, so the source emits alpha. Adding aluminium made almost no difference, so there is little or no beta. The remaining count of about 100 per minute is likely to be gamma, with some background radiation.
Explain why alpha radiation is the most ionising of the three types but the least penetrating.
Mark scheme
alpha particles are large / have a big charge, so they ionise many atoms (1); each ionisation transfers energy from the alpha particle (1); so it loses its energy quickly and only travels a short distance / is stopped by paper (1)
Model answer
Alpha particles ionise a very large number of atoms along their path. Each ionisation takes some energy from the particle, so it quickly runs out of energy and stops after a few centimetres in air.
Radiation emitted by a source can be harmful. State why ionising radiation can be harmful to living cells.
Mark scheme
it can damage / kill cells (1); it can cause mutations in DNA / cancer (1)
Model answer
Ionising radiation can damage or kill cells, and it can cause mutations in DNA, which may lead to cancer.
(Edexcel) State what a positron is, and give one way in which it is different from an electron.
Mark scheme
the antiparticle of the electron / same mass as an electron (1); it has a positive charge (+1) (1)
Model answer
A positron is the antiparticle of the electron. It has the same mass, but a charge of +1 instead of −1.
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