Radioactive decay and types of radiationIB MYP Physics: Subtopic test

1. 1
   A hospital physicist in Manchester stores three radioactive sources, one that emits alpha particles, one that emits beta particles and one that emits gamma rays. She must choose suitable shielding for each source and check which types of radiation are most harmful to living cells.

   (a)

   Which type of radiation is stopped by a sheet of paper?

   [1 mark]

   • AGamma rays
   • BBeta particles
   • CAlpha particles
   • DAll three types

   (b)

   Which shielding would reduce the amount of gamma radiation passing through the most?

   [1 mark]

   • AA thick block of lead
   • BA sheet of paper
   • CA 3 mm sheet of aluminium
   • DA few centimetres of air

   (c)

   Compare the ionising power and the penetrating power of alpha particles and gamma rays.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Uranium-238 has atomic number 92. Its nuclei are unstable. A uranium-238 nucleus decays by emitting an alpha particle and forms a nucleus of thorium (symbol Th). The thorium-234 nucleus then decays by beta emission to form protactinium (symbol Pa).

   (a)

   What is an alpha particle?

   [1 mark]

   • AA fast-moving electron
   • BAn electromagnetic wave
   • CA proton and an electron joined together
   • DA helium nucleus

   (b)

   What happens inside a thorium-234 nucleus when it emits a beta particle?

   [1 mark]

   • AA proton changes into a neutron and an electron is emitted
   • BA neutron changes into a proton and a fast electron is emitted
   • CTwo protons and two neutrons are emitted
   • DEnergy is emitted but no particles change

   (c)

   State the mass number and the atomic number of the thorium nucleus formed when uranium-238 decays by alpha emission.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates how well two materials absorb gamma radiation. She holds a Geiger-Muller tube 10 cm from a gamma source and records the number of counts in 60 seconds. With the source removed she records a background count of 12 in 60 seconds. With nothing between the source and the tube she records 612 counts. With a 5 mm sheet of aluminium in the way she records 598 counts, and with a 5 mm sheet of lead in the way she records 214 counts.

   (a)

   Identify the independent variable, the dependent variable and one control variable in this investigation.

   [3 marks]

   (b)

   Process the data to find the corrected count for each sheet, and explain what the results show about the absorption of gamma radiation.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A school science department keeps a sealed americium-241 source, which emits alpha particles, in a locked, lead-lined cupboard. A group of parents ask the head teacher whether the school should keep radioactive sources at all. The head teacher explains that radioactive decay is spontaneous and random, and that a Geiger-Muller tube in the classroom clicks every few seconds even when no source is nearby.

   (a)

   Explain what is meant by saying that radioactive decay is spontaneous and random, and explain why the counts in the classroom must be corrected for background radiation.

   [6 marks]

   (b)

   Discuss whether the school should keep a sealed radioactive source for demonstrations, and give a justified conclusion.

   [6 marks]

   Total for question 4: 12 marks

End of questions