RadioactivityEdexcel GCSE Physics: Topic test

20 questions, 54 marks

Edexcel GCSE Physics

Radioactivity topic test

Total 54 marks

Name

Class

Date

1
A physics teacher demonstrates the historical development of atomic models to a class. She explains that before the early 1900s scientists imagined an atom as a ball of positive charge with electrons embedded inside it like fruit in a pudding, and that this picture was later replaced after an experiment in which a stream of alpha particles was fired at gold foil and most particles passed straight through, but a very small number bounced back at large angles.
(a)
What was this earlier model of the atom, in which negatively charged electrons sit within a ball of spread-out positive charge, known as?
[1 mark]
AThe plum pudding model
BThe nuclear model
CThe Bohr model
DThe shell model
(b)
What did the very small number of alpha particles that bounced back at large angles show about the structure of the gold atoms?
[1 mark]
AThat atoms have no charge at all
BThat most of an atom's mass and positive charge is concentrated in a tiny, dense nucleus
CThat electrons are much heavier than the nucleus
DThat gold atoms contain no neutrons
(c)
The teacher goes on to explain that most alpha particles passed straight through the gold foil without being deflected at all. State what this observation showed about the structure of a gold atom.
[2 marks]
Total for question 1: 4 marks
2
A sample of the isotope strontium-90 is monitored in a school laboratory. Strontium-90 is unstable and decays by beta-minus emission to form yttrium-90. In this decay, a neutron inside the strontium nucleus changes into a proton, and an electron is emitted from the nucleus at high speed.
(a)
What happens to the mass (nucleon) number and the atomic (proton) number of the nucleus during this beta-minus decay?
[1 mark]
AThe mass number increases by one and the atomic number stays the same
BBoth the mass number and the atomic number stay the same
CThe mass number stays the same and the atomic number increases by one
DThe mass number decreases by four and the atomic number decreases by two
(b)
Strontium-90 has atomic number 38. What is the atomic number of the yttrium-90 nucleus produced?
[1 mark]
A36
B37
C38
D39
(c)
Write a balanced nuclear equation for the beta-minus decay of strontium-90 (atomic number 38, mass number 90) into yttrium (symbol Y), including the emitted beta particle, and check that both mass number and charge balance.
[2 marks]
Total for question 2: 4 marks
3
A geology student takes a Geiger–Müller tube and counter into a disused mine to measure background radiation levels at different depths underground. She records a much higher count rate close to certain rock faces containing granite than she does in open air outside the mine entrance, and also notices that the count rate recorded by the same detector varies slightly between repeated readings taken at the exact same spot.
(a)
Suggest why the count rate recorded near the granite rock faces is higher than in the open air outside the mine, and explain why repeated readings taken at exactly the same spot still vary slightly from each other.
[3 marks]
(b)
State four other sources of background radiation, besides rocks such as granite, that the student might need to account for when interpreting her readings, whether they originate from the Earth or from space.
[4 marks]
Total for question 3: 7 marks
4
An energy company is comparing two possible future power stations. The first would be a nuclear fission power station, in which uranium-235 nuclei are split by absorbing slow-moving neutrons. The second is an experimental nuclear fusion reactor, still under development, which aims to join together small hydrogen nuclei at extremely high temperatures and pressures to release energy, in the same way that reactions occur inside the Sun.
(a)
Explain how the fission of a uranium-235 nucleus releases energy, and describe how a controlled chain reaction is maintained and controlled inside a working nuclear fission reactor.
[6 marks]
(b)
Explain the key differences between nuclear fission and nuclear fusion in terms of what happens to the nuclei involved, and explain why achieving a controlled, practical fusion power station on Earth has proved so difficult.
[6 marks]
Total for question 4: 12 marks
5
A chemistry technician is comparing two samples. Sample X contains atoms of the isotope carbon-12, each with 6 protons and 6 neutrons in the nucleus. Sample Y contains atoms of the isotope carbon-14, each with 6 protons but 8 neutrons in the nucleus. Both samples start as neutral atoms, but during an experiment some of the atoms in sample X lose one outer electron each, forming positive ions.
(a)
What term describes carbon-12 and carbon-14, given that they have the same number of protons but different numbers of neutrons?
[1 mark]
AIsotopes
BIsobars
CIons
DIsomers
(b)
A neutral carbon-12 atom has 6 protons and 6 electrons. When one of these atoms loses one outer electron to form a positive ion, what is the overall charge of the resulting ion?
[1 mark]
A0
B+1
C-1
D+2
(c)
Explain why carbon-12 and carbon-14 atoms have almost identical chemical properties, despite having different masses.
[2 marks]
Total for question 5: 4 marks
6
A sample of a radioactive isotope used in a school demonstration has an initial activity of 800 Bq when first measured. A student records the activity of the sample at regular intervals afterwards using a Geiger–Müller tube and counter, and finds that the activity has fallen to 100 Bq after a total of 45 minutes has passed.
(a)
What is meant by the half-life of a radioactive isotope?
[1 mark]
AThe time taken for the mass of the sample to fall to zero
BThe time taken for a sample to become completely safe to handle
CThe time taken for half of the undecayed nuclei in a sample to decay, or for its activity to halve
DThe total time over which any radioactivity can be detected from a sample
(b)
The activity fell from 800 Bq to 100 Bq. How many half-lives does this represent?
[1 mark]
A2
B4
C8
D3
(c)
Using your answer to the previous part and the fact that this fall in activity took a total of 45 minutes, calculate the half-life of the isotope in minutes, showing your working.
[2 marks]
Total for question 6: 4 marks
7
A hospital physicist prepares a radioactive tracer for a PET (positron emission tomography) scan. The tracer isotope has a very short half-life and is manufactured in a small cyclotron located inside the hospital itself, only a short time before it is injected into the patient's bloodstream. During preparation, a small amount of the tracer solution is accidentally spilled onto a technician's glove.
(a)
Explain why the tracer isotope used for the PET scan must be produced on-site at the hospital, rather than being manufactured at a distant factory and transported in, and explain why the same short half-life is also beneficial for the patient's safety once the scan is complete.
[3 marks]
(b)
Explain the difference between contamination and irradiation, using the technician's spilled glove to illustrate contamination, explain why the technician should remove the glove immediately rather than simply continuing to work while wearing it, and state one further precaution the technician should take afterwards.
[4 marks]
Total for question 7: 7 marks
8
A science museum exhibit compares two energy sources: a small radioactive check-source used to calibrate classroom Geiger counters, which decays naturally and gives out radiation continuously at a slowly falling rate, and a scale model explaining how the Sun generates its energy by fusing hydrogen nuclei together in its core. A visitor asks a museum guide to explain how these two very different physical processes both end up releasing energy.
(a)
Explain, in terms of the nucleus and mass, why the spontaneous radioactive decay of an unstable nucleus in the classroom check-source releases energy, and explain why this process happens at an unpredictable, random time for any one individual nucleus even though the overall activity of a large sample falls in a predictable pattern.
[6 marks]
(b)
Explain how nuclear fusion inside the Sun's core releases energy, and explain why this fusion process can take place continuously inside the Sun but does not happen spontaneously between hydrogen nuclei under everyday conditions on Earth.
[6 marks]
Total for question 8: 12 marks

End of questions