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HSC Physics 9.8 Quanta to Quarks Example Questions
Markers comments, sample answers and marking guidelines
Example Question 1 (2012 HSC Physics exam) Question 34
Markers comments Question 34 b) i)
In better responses, candidates linked the requirement for an increasing number of
neutrons with an uncontrolled nuclear chain reaction.
Markers comments Question 34 c)
In better responses, candidates linked the work of Louis de Broglie to matter waves and
included a discussion of the properties of neutrons.
Sample answer Question 34 b) i)
Three key conditions are required to produce an uncontrolled nuclear reaction:
1. A block of an isotope with nuclei that spontaneously fission when they absorb a neutron
2. Each fission reaction should produce, on average, more than 1 free neutron per fission
3. The shape of the block of isotope and the kinetic energy of the released neutrons should
be such that, on average, more than one fission occurs per previous fission event
Sample answer Question 34 c)
Based on the work of de Broglie we know that a beam of neutrons with a known kinetic
energy and hence momentum, has a certain characteristic wavelength. This wave character
means that the regular repeating lattice of the nuclei in the metal crystal will diffract the
neutron beam. Because the neutrons are neutral they are not affected by the electrons in
the crystal and only scatter from the nuclei.
Marking guidelines Question 34 b) i)
Criteria
Marks
• Shows a clear understanding of the key requirements
3
• Shows a clear understanding of the majority of the key requirements
2
• Shows a clear understanding of at least one of the key requirements
1
Marking guidelines Question 34 c)
Criteria
Marks
• Shows a clear understanding of the wave nature of moving neutrons
4
• Shows a clear understanding that the periodic arrangement of metal nuclei will
HSC Physics 9.8 Quanta to Quarks Example Questions – Marking guidelines
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diffract the neutrons in turn revealing their arrangement
• Shows a clear understanding that the neutral neutrons will not scatter from the
electrons
• Connects the above points into a coherent description
• Shows some understanding of the above points and some understanding of how
they are related
3
• Shows some understanding of the above points
1-2
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Example Question 2 (2011 HSC Physics exam) Question 34
Markers’ Comments Question 34 a)
Most candidates correctly named an isotope and its mass number. In better responses,
candidates linked the named isotope with a correct use in agriculture.
Markers’ Comments Question 34 b) i)
Most candidates linked the connection between control rods, neutron number and reaction
rate. Better responses included the moderator as also affecting reaction rate.
Sample answer Question 34 a)
Phosphorus-32 is used to measure the rate at which phosphorus is taken up by a plant.
Phosphorus is an important plant nutrient.
Sample answer Question 34 b) i)
• The higher the number of fuel rods inserted into the reaction vessel, the faster the rate of
the reaction.
• A moderator slows neutrons, making it more likely for these neutrons to be captured by a
fissionable nucleus.
• Control rods absorb neutrons. The larger the number of control rods inside the reaction
vessel, the fewer the neutrons and the slower the rate.
• Most modern nuclear reactors do not change the amount of moderator in the reaction
vessel.
Consequently, the rate of reaction in a nuclear reactor will increase when:
– more fuel rods are inserted
– control rods are removed.
The rate will decrease when:
– fewer fuel rods are inserted
– control rods are added.
Marking guidelines Question 34 a)
Criteria
Marks


Names a radioisotope that is used in agriculture
Describes its use
2

Names a radioisotope
OR
1
HSC Physics 9.8 Quanta to Quarks Example Questions – Marking guidelines
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
Identifies a use
Marking guidelines Question 34 b) i)
Criteria
Marks

Describes the relationship between neutrons, their exposure to a
moderator and the number of control rods in the reactor vessel and
the resulting rate of reaction
4

Outlines any TWO of the above factors AND describes their
relationship to the reaction rate
3
OR

Outlines all THREE factors

2

Outlines ONE factor and its relationship to the reaction rate
OR
Outlines TWO factors

Outlines ONE factor
1
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Example Question 3 (2008 HSC Physics exam) Question 31
Sample answer Question 31 b) i)
90 protons, 137 neutrons
Sample answer Question 31 b) ii)
Francium-223 → Astatine-219 + α
OR
223
Fr  219At + α
Marking guidelines Question 31 b) i)
Criteria
• States the numbers correctly
Marks
1
Marking guidelines Question 31 b) ii)
Criteria
Marks
• Writes the correct equation, including balanced and atomic mass in words
or symbols
2
• Writes an equation for the transition with at most one mistake or
omission
1
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Example Question 4 (2007 HSC Physics exam) Question 31
Markers comments Question 31 b) i)
Better responses provided the main features of the investigation which included the
position of the radioactive source and an observation of the radiation.
Markers comments Question 31 b) ii)
Better responses correctly named the radio-isotope and clearly showed the link between its
radioactive properties and its use.
Marking guidelines Question 31 b) i)
Criteria
Marks

Provides features of the investigation
2

Outlines the investigation
OR
Provides ONE feature of the investigation
1

Marking guidelines Question 31 b) ii)
Criteria
Marks


Selects two different isotopes, each relevant to the nominated field
Shows how the properties of each are related to their respective
uses
3-4

Correctly chooses an isotope relevant to a nominated field and
shows how the properties are related to its use
1-2
OR

Selects two different isotopes each relevant to the nominated field
but with little or no explanation
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Example Question 5 (2003 HSC Physics exam) Question 31
Markers’ Comments Question 31 c) i) and ii)
The better responses linked the isotope production to its parent reaction. In the poorer
responses, candidates did not know the processes involved in generating radioactive
isotopes, although they could explain the uses of the isotopes.
Marking guidelines Question 31 c) i)
Criteria
Marks
• Reaction 2 because part of radioactive decay series
OR
• U-238 is naturally occurring
OR
• No energy has been put in
2
OR
• No neutrons are added to it
OR
• Reaction 3 — geological evidence in Africa
• Reaction 2
OR
1
• Reaction 3
Marking guidelines Question 31 c) ii)
Criteria
Marks
• Reaction 3
• Used nuclear reactors
• For power or weapons or radioisotope production or electrical energy
production
• Plus details of named application
OR
3
• Reaction 1
• Artificial transmutation
• Production of radioisotopes OR
• Production of plutonium or fast breeder reaction
• Correctly names reaction 1 or 3
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• Identifies one application
OR
• Describes a feature
• Names one reaction (1 or 3)
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