name: atomic structure - aston academy gcse physics€¦ · against atomic number and draw a line...

Atomic StructureHigh Demand Questions

Name: ________________________

Class: ________________________

Date: ________________________

Time: 142 minutes

Marks: 140 marks

Comments:

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In the early part of the 20th century, scientists used the ‘plum pudding’ model to explain thestructure of the atom.

Following work by Rutherford and Marsden, a new model of the atom, called the ‘nuclear’ model,was suggested.

Describe the differences between the two models of the atom.

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(Total 4 marks)

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There are many different isotopes of gold. The isotope, gold-198, is radioactive.An atom of gold-198 decays by emitting a beta particle.

(a) Complete the following sentences.

All atoms of gold have the same number of ________________________________

and the same number of __________________________________ .

The atoms from different isotopes of gold have different numbers of ____________ .

A beta particle is an __________________________________ emitted

from the __________________________________ of an atom.

(3)

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(b) The graph shows how the count rate from a sample of gold-198 changes with time.

Time in days

Use the graph to calculate the half-life of gold-198.

Show clearly on the graph how you obtain your answer.

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Half-life = ________________ days

(2)

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(c) The diagram shows a map of a river and the river estuary.

Environmental scientists have found that water flowing into one part of the river estuary ispolluted. To find where the pollution is coming from, the scientists use a radioactive isotope,gold-198.

The gold-198 is used to find where the pollution is coming from.

Explain how.

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(2)

(Total 7 marks)

In 2011 an earthquake caused severe damage to a nuclear power station in Japan.

The damage led to the release of large amounts of radioactive iodine-131 into theatmosphere.

(a) The table gives some information about an atom of iodine-131 .

Complete the table.

mass number 131

number of protons 53

number of neutrons

(1)

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(b) Complete the sentence.

The number of protons in an atom is called the proton number or

the _______________ number.

(1)

(c) An atom of iodine-131 decays into an atom of xenon (Xe) by emitting a beta particle.

(i) The decay of iodine-131 can be represented by the equation below.

Complete the equation by writing the correct number in each of the two boxes.

(2)

(ii) A sample of rainwater contaminated with iodine-131 gives a count rate of 1200counts per second.

Calculate how many days it will take for the count rate from the sample of rainwaterto fall to 75 counts per second.

Half-life of iodine-131 = 8 days

Show clearly how you work out your answer.

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_______________ days

(2)

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(iii) If people drink water contaminated with iodine-131, the iodine-131 builds up in thethyroid gland. This continues until the thyroid is saturated with iodine-131 and cannotabsorb any more. The radiation emitted from the iodine-131 could cause cancer ofthe thyroid.

In Japan, people likely to be drinking water contaminated with iodine-131 wereadvised to take tablets containing a non-radioactive isotope of iodine.

Suggest why this advice was given.

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(2)

(Total 8 marks)

A teacher used the equipment shown in the diagram to measure the count rate at differentdistances from a radioactive source.

Metre rule

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(a) Her results are shown in Table 1.

Table 1

Distance in metresCount rate in counts

per minuteCorrected count rate in

counts per minute

0.4 143 125

0.6 74 56

0.8 49 31

1.0 38 20

1.2 32 14

1.4 28 10

1.6 18 0

1.8 18 0

2.0 18 0

The background count rate has been used to calculate the corrected count rate.

(i) What is the value of the background count rate?

Background count rate = _______________ counts per minute

(1)

(ii) What information does the corrected count rate give?

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(1)

(iii) The radioactive source used in the demonstration emits only one type of radiation.

The radioactive source is not an alpha emitter.

How can you tell from the data in the table?

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(1)

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(iv) Plot a graph of corrected count rate against distance for distances between 0.4 m and1.4 m.

Draw a line of best fit to complete the graph.

Distance in metres

(3)

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(v) The ‘half-distance’ is the distance a detector has to be moved away from aradioactive source for the corrected count rate to halve.

A student has the hypothesis:A radioactive source has a constant ‘half-distance’.

Table 1 has been repeated for your information.

Table 1

Distance in metresCount rate in counts

per minuteCorrected count rate in

counts per minute

0.4 143 125

0.6 74 56

0.8 49 31

1.0 38 20

1.2 32 14

1.4 28 10

1.6 18 0

1.8 18 0

2.0 18 0

Use Table 1 to determine if the hypothesis is correct for this radioactive source.

You should use calculations in your answer.

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(3)

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(b) A teacher places a beta source and a detector in a magnetic field.

The arrangement of the magnetic field is shown.

The teacher repeated the experiment with the magnetic field in a different direction.

A set of results is shown in Table 2.

Table 2

Distancebetween sourceand detector in

metres

Count rate incounts per

minute withoutmagnetic field

Count rate incounts perminute in

Experiment 1

Count rate incounts perminute in

Experiment 2

0.8 48 48 32

(i) Describe and explain the effect of the magnetic field on the count rate detected bythe detector.

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(2)

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(ii) The experiment is repeated with a different distance between the source and thedetector.

Table 3 shows the repeated results.

Table 3

Distance betweensource and

detectorin metres

Count ratein counts per

minute withoutmagnetic field


minute inExperiment 1


minute inExperiment 2

1.8 19 18 20

Explain these results.

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(2)

(Total 13 marks)

(a) A teacher used a Geiger-Műller (GM) tube and counter to measure the backgroundradiation in her laboratory.

The teacher reset the counter to zero, waited one minute and then took the count reading.The teacher repeated the procedure two more times.

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(i) Background radiation can be either from natural sources or from man-made sources.

Name one man-made source of background radiation.

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(1)

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(ii) The three readings taken by the teacher are given in the table.

Count afterone minute

15

24

18

The readings given in the table are correct.

Why are the readings different?

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(1)

(b) Some scientists say they have found evidence to show that people living in areas of highnatural background radiation are less likely to develop cancer than people living in similarareas with lower background radiation.

The evidence these scientists found does not definitely mean that the level of backgroundradiation determines whether a person will develop cancer.

Suggest a reason why.

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(1)

(c) An atom of the isotope radon-222 emits an alpha particle and decays into an atom ofpolonium.

An alpha particle is the same as a helium nucleus. The symbol below represents an alphaparticle.

(i) How many protons and how many neutrons are there in an alpha particle?

Number of protons = ________

Number of neutrons = ________

(2)

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(ii) The decay of radon-222 can be represented by the equation below.

Complete the equation by writing the correct number in each of the two boxes.

(2)

(d) The graph shows how, in a sample of air, the number of radon-222 nuclei changes withtime.

Time in days

Use the graph to find the half-life of radon-222.

Show clearly on the graph how you obtain your answer.

Half-life = _________________________ days

(2)

(Total 9 marks)

(a) Nuclear power stations generate about 14% of the world’s electricity.

(i) Uranium-235 is used as a fuel in some nuclear reactors.

Name one other substance used as a fuel in some nuclear reactors.

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(1)

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(ii) Energy is released from nuclear fuels by the process of nuclear fission.

This energy is used to generate electricity.

Describe how this energy is used to generate electricity.

Do not explain the nuclear fission process.

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(3)

(b) The diagram shows the nuclear fission process for an atom of uranium-235.

Complete the diagram to show how the fission process starts a chain reaction.

(2)

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(c) The diagram shows the cross-section through a nuclear reactor.

The control rods, made from boron, are used to control the chain reaction. Boron atomsabsorb neutrons without undergoing nuclear fission.

Why does lowering the control rods reduce the amount of energy released each secondfrom the nuclear fuel?

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(2)

(Total 8 marks)

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Atoms are different sizes.

One of the heaviest naturally occurring stable elements is lead.

Two of its isotopes are lead-206 ( ) and lead-208 ( ).

(a) (i) What is meant by ‘isotopes’?

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(2)

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(ii) How many protons are in the nucleus of a atom?

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(1)

(iii) How many neutrons are in the nucleus of a atom?

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(1)

(b) A nucleus can be accelerated in a particle accelerator and directed at a large nucleus. Thisproduces a heavy nucleus that will decay after a short time.

This is shown in Figure 1.

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(i) In 1984, nuclei of iron (Fe) were directed at nuclei of lead (Pb). This produced nucleiof hassium (Hs).

Complete the equation for this reaction by writing numbers in the empty boxes.

(3)

(ii) Use the correct answer from the box to complete the sentence.

an electron a proton a neutron

The particle X in part (b)(i) is _________________________________ .

(1)

(iii) After acceleration the iron nuclei travel at a steady speed of one-tenth of the speed oflight.

The speed of light is 3.00 × 108 m/s.

Calculate the time taken for the iron nuclei to travel a distance of 12 000 m.

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Time taken = ____________________ s

(2)

(iv) Linear accelerators, in which particles are accelerated in a straight line, are not usedfor these experiments. Circular particle accelerators are used.

Suggest why.

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(3)

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(c) Hassium-265 ( ) decays by alpha emission with a half-life of 0.002 seconds.

(i) What is meant by ‘half-life’?

Tick ( ) two boxes.

Tick ( )

The average time for the number of nuclei to halve

The time for count rate to be equal to background count

The time for background count to halve

The time for count rate to halve

(2)

(ii) Complete the equation for the decay of Hs-265 by writing numbers in the emptyboxes.

(2)

(d) The table below shows how the atomic radius of some atoms varies with atomic number.

Atomicnumber

Atomic radius inpicometres (pm)

15 100

35 115

50 130

70 150

95 170

1 pm = 10–12 m

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(i) On Figure 2, use the data from the table above to plot a graph of atomic radiusagainst atomic number and draw a line of best fit.

Two points have been plotted for you.

Figure 2

(2)

(ii) Scientists believe that the element with atomic number 126 can be produced and thatit will be stable.

Use your graph in Figure 2 to predict the atomic radius of an atom with atomicnumber 126.

Atomic radius = ____________________ pm

(1)

(Total 20 marks)

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(a) There are many isotopes of the element molybdenum (Mo).

What do the nuclei of different molybdenum isotopes have in common?

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(1)

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(b) The isotope molybdenum-99 is produced inside some nuclear power stations from thenuclear fission of uranium-235.

(i) What happens during the process of nuclear fission?

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(1)

(ii) Inside which part of a nuclear power station would molybdenum be produced?

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(c) When the nucleus of a molybdenum-99 atom decays, it emits radiation and changes into anucleus of technetium-99.

Mo Tc + Radiation

What type of radiation is emitted by molybdenum-99?

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Give a reason for your answer.

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(2)

(d) Technetium-99 has a short half-life and emits gamma radiation.

What is meant by the term ‘half-life’?

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(1)

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(e) Technetium-99 is used by doctors as a medical tracer. In hospitals it is produced inside atechnetium generator by the decay of molybdenum-99 nuclei.

(i) The figure below shows how the number of nuclei in a sample of molybdenum-99changes with time as the nuclei decay.

Time in days

A technetium generator will continue to produce sufficient technetium-99 until 80% ofthe original molybdenum nuclei have decayed.

After how many days will a source of molybdenum-99 inside a technetium-99generator need replacing?

Show clearly your calculation and how you use the graph to obtain your answer.

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Number of days = ______________________

(2)

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(ii) Medical tracers are injected into a patient’s body; this involves some risk to thepatient’s health.

Explain the risk to the patient of using a radioactive substance as a medical tracer.

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(2)

(iii) Even though there may be a risk, doctors frequently use radioactive substances formedical diagnosis and treatments.

Suggest why.

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(1)

(Total 11 marks)

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Nuclear fission and nuclear fusion are two processes that release energy.

(a) The following nuclear equation represents the fission of uranium-235 (U-235).

Chemical symbols:

• Ba = barium

• Kr = krypton

• = neutron

Describe the process of nuclear fission.

Use the information in the equation.

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(4)

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(b) Explain what happens in the process of nuclear fusion.

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(3)

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(c) Fission reactors are used in nuclear power stations.

Engineers are developing fusion reactors for use in power stations.

Fusion uses isotopes of hydrogen called deuterium and tritium.

• Deuterium is naturally occurring and can be easily extracted from seawater.

• Tritium can be produced from lithium. Lithium is also found in seawater.

The table shows the energy released from 1 kg of fusion fuel and from 1 kg of fission fuel.

Type of fuelEnergy released from 1 kg

of fuel in joules

Fusion 3.4 × 1014

Fission 8.8 × 1013

Suggest two advantages of the fuel used in a fusion reactor compared with the fuel used ina fission reactor.

1. _________________________________________________________________

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2. _________________________________________________________________

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(2)

(Total 9 marks)

Electricity is generated in a nuclear power station.

Fission is the process by which energy is released in the nuclear reactor.

(a) Figure 1 shows the first part of the nuclear fission reaction.

Complete Figure 1 to show how the fission process starts a chain reaction.

Figure 1

(3)

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(b) Figure 2 shows the inside of a nuclear reactor in a nuclear power station.

Figure 2

In a nuclear reactor a chain reaction occurs, which causes neutrons to be released.

The control rods absorb neutrons.

The control rods can be moved up and down.

Explain how the energy released by the chain reaction is affected by moving the controlrods.

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(2)

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(c) Figure 3 shows how the power output of the nuclear reactor would change if the controlrods were removed.

Figure 3

Calculate the rate of increase of power output at 10 minutes.

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Rate of increase of power output = _________ MW / minute

(2)

(Total 7 marks)

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Nuclear power stations generate electricity through nuclear fission. Electricity can also begenerated by burning shale gas.

(a) Shale gas is natural gas trapped in rocks. Shale gas can be extracted by a process calledfracking. There is some evidence that fracking causes minor earthquakes. Burning shalegas adds carbon dioxide to the atmosphere.

Describe the advantages of nuclear power compared with the use of shale gas to generateelectricity.

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(3)

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(b) What is the name of one fuel used in nuclear power stations?

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(1)

(c) Describe the process of nuclear fission.

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(4)

(Total 8 marks)

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Smoke alarms contain an alpha radiation source and a radiation detector.

Figure 1 shows part of the inside of a smoke alarm.

Figure 1

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(a) The smoke alarm stays off while alpha radiation reaches the detector.

Why does the alarm switch on when smoke particles enter the plastic casing?

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(1)

(b) Why is it safe to use a source of alpha radiation in a house?

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(1)

(c) The smoke alarm would not work with a radiation source that emits beta or gammaradiation.

Explain why.

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(2)

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(d) Figure 2 shows how the count rate detected from the radiation source in the smoke alarmchanges with time.

Figure 2

The smoke alarm switches on when the count rate falls to 80 counts per second.

Explain why the radiation source inside the smoke alarm should have a long half-life.

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(2)

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(e) Figure 3 shows a patient who has been injected with a radioactive source for medicaldiagnosis.

Figure 3

Explain the ideal properties of a radioactive source for use in medical diagnosis.

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(4)

(Total 10 marks)

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In the early 20th century, scientists developed an alpha particle scattering experiment using goldfoil.

The diagram shows the paths of some of the alpha particles in the alpha particle scatteringexperiment.

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(a) Explain how the paths of the alpha particles were used to develop the nuclear model of theatom.

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(4)

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(b) Niels Bohr adapted the nuclear model by suggesting electrons orbited the nucleus atspecific distances.

Explain how the distance at which an electron orbits the nucleus may be changed.

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(3)

(Total 7 marks)

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A student models the random nature of radioactive decay using 100 dice.

He rolls the dice and removes any that land with the number 6 facing upwards.

He rolls the remaining dice again.

The student repeats this process a number of times.

The table below shows his results.

Roll number Number of dice remaining

0 100

1 84

2 70

3 59

4 46

5 40

6 32

7 27

8 23

(a) Give two reasons why this is a good model for the random nature of radioactive decay.

1. _________________________________________________________________

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2. _________________________________________________________________

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(2)

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(b) The student’s results are shown in Figure 1.

Figure 1

Use Figure 1 to determine the half-life for these dice using this model.

Show on Figure 1 how you work out your answer.

Half-life = ________________________ rolls

(2)

(c) A teacher uses a protactinium (Pa) generator to produce a sample of radioactive materialthat has a half-life of 70 seconds.

In the first stage in the protactinium generator, uranium (U) decays into thorium (Th) andalpha (α) radiation is emitted.

The decay can be represented by the equation shown in Figure 2.

Figure 2

Determine the atomic number of thorium (Th) 234.

Atomic number = ______________________

(1)

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(d) When protactinium decays, a new element is formed and radiation is emitted.

The decay can be represented by the equation shown in Figure 3.

Figure 3

When protactinium decays, a new element, X, is formed.

Use information from Figure 2 and Figure 3 to determine the name of element X.

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(e) Determine the type of radiation emitted as protactinium decays into a new element.

Give a reason for your answer.

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(2)

(f) The teacher wears polythene gloves as a safety precaution when handling radioactivematerials.

The polythene gloves do not stop the teacher’s hands from being irradiated.

Explain why the teacher wears polythene gloves.

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(2)

(Total 10 marks)

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Many countries use nuclear power stations to generate electricity.Nuclear power stations use the process of nuclear fission to release energy.

(a) (i) What is nuclear fission?

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(1)

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(ii) Plutonium-239 is one substance used as a fuel in a nuclear reactor. For nuclearfission to happen, the nucleus must absorb a particle.

What type of particle must be absorbed?

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(1)

(b) Nuclear fusion also releases energy.Nuclear fusion happens at very high temperatures. A high temperature is needed toovercome the repulsion force between the nuclei.

(i) Why is there a repulsion force between the nuclei of atoms?

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(1)

(ii) Where does nuclear fusion happen naturally?

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(1)

(c) In 1991, scientists produced the first controlled release of energy from an experimentalnuclear fusion reactor. This was achieved by fusing the hydrogen isotopes, deuterium andtritium.

Deuterium is naturally occurring and can easily be extracted from seawater. Tritium can beproduced from lithium. Lithium is also found in seawater.

The table gives the energy released from 1 kg of fusion fuel and from 1 kg of fission fuel.

Type of fuelEnergy released from1 kg of fuel in joules

Fusion fuel 3.4 × 1014

Fission fuel 8.8 × 1013

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(i) Suggest two advantages of the fuel used in a fusion reactor compared with plutoniumand the other substances used as fuel in a fission reactor.

1. ____________________________________________________________

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2. ____________________________________________________________

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(2)

(ii) Some scientists think that by the year 2050 a nuclear fusion power station capable ofgenerating electricity on a large scale will have been developed.

Suggest one important consequence of developing nuclear fusion power stations togenerate electricity.

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(1)

(d) Tritium is radioactive.

After 36 years, only 10 g of tritium remains from an original sample of 80 g.

Calculate the half-life of tritium.

Show clearly how you work out your answer.

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Half-life = __________________ years

(2)

(Total 9 marks)

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Mark schemes

any two pairs from:

to gain credit it must be clear which model is being described

do not accept simple descriptions of the diagram withoutcomparison

• nuclear model mass is concentrated at the centre / nucleus (1)

accept the nuclear model has a nucleus / the plum pudding modeldoes not have a nucleus for 1 mark

plum pudding model mass is evenly distributed (1)

• nuclear model positive charge occupies only a small part of the atom (1)

plum pudding model positive charge spread throughout the atom (1)

• nuclear model electrons orbit some distance from the centre (1)

accept electrons in shells / orbits provided a valid comparison ismade with the plum pudding model

plum pudding electrons embedded in the (mass) of positive (charge) (1)

do not accept electrons at edge of plum pudding

• nuclear model the atom mainly empty space (1)

plum pudding model is a ‘solid’ mass (1)

[4]

1

(a) protons, electrons

both required, either order1

2

neutrons1

electron, nucleus

both required, this order1

(b) 2.7 (days)

allow 1 mark for showing correct use of the graph2

(c) put source into water at one point on bank

accept the idea of testing different parts of the river bank at differenttimes

1

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see if radiation is detected in polluted area

accept idea of tracing

or

put source into water at three points on bank (1)see if radiation is detected downstream of factory or farmland or sewage treatmentworks (1)

1

[7]

(a) 7813

(b) atomic1

(c) (i) 131

correct order only1

541

(ii) 32 (days)

allow 1 mark for showing 4 half-lives provided no subsequent step2

(iii) limits amount of iodine-131 / radioactive iodine that can be absorbed

accept increases level of non-radioactive iodine in thyroid

do not accept cancels out iodine-1311

so reducing risk of cancer (of the thyroid)

accept stops risk of cancer (of the thyroid)1

[8]

(a) (i) 1814

(ii) the count rate for the source1

(iii) the alpha radiation would not cover such a distance1

(iv) plots correct to within ½ small square

allow 1 mark for 4 correct points plotted2

correct curve through points as judged by eye1

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(v) two attempts at finding ‘half-distance’ using the table

20 to 10 cpm d = 0.4 m125 to 56 cpm d = 0.2 m31 to 14 cpm d = 0.4 m

allow 1 mark for one attempted comparison2

obeyed or not obeyed

dependent on previous two marks1

(b) (i) there is no effect on the count rate in experiment 1 because the field is parallelor beta particles are not deflected or there is no force

1

count rate is reduced in experiment 2 because field is perpendicular or betaparticles are deflected or there is a force

1

(ii) only background radiation (as beta do not travel as far)1

slightly different values show the random nature of radioactive decay1

[13]

(a) (i) any one from:

• nuclear power (stations)

accept nuclear wasteaccept coal power stations

• nuclear weapons (testing)

accept nuclear bombs / fallout

• nuclear accidents

accept named accident, eg Chernobyl or Fukushima

accept named medical procedure which involves a radioactivesourceaccept radiotherapyaccept X-raysaccept specific industrial examples that involve a radioactive source

nuclear activity / radiation is insufficient

smoke detectors is insufficient1

5

(ii) (radioactive decay) is a random process

accept an answer in terms of background / radiation varies (fromone point in time to another)

1

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(b) any one from:

• (maybe) other factors involved

accept a named ‘sensible’ factor, eg smoking

• evidence may not be valid

accept not enough data

• may not have (a complete) understanding of the process (involved)1

(c) (i) 21

21

(ii) 218

correct order only1

841

(d) 3.8 (days)

allow 1 mark for showing correct method using the graph providedno subsequent steps

correct answers obtained using numbers other than 800 and 400gain 2 marks provided the method is shown

2

[9]

(a) (i) plutonium (239)

accept Pu / Thorium / MOX (mixed oxide)

do not accept uranium-238 or hydrogen1

6

(ii) (energy) used to heat water and1

produce (high pressure) steam1

the steam drives a turbine (which turns a generator)1

(b) Neutron(s) shown ‘hitting’ other U-235 nuclei

one uranium nucleus is sufficient1

U-235 nuclei (splitting) producing 2 or more neutrons1

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(c) any two from:

• neutrons are absorbed (by boron / control rods)

• there are fewer neutrons

• chain reaction slows down / stops

accept fewer reactions occur2

[8]

(a) (i) (atoms with the) same number of protons

allow same atomic number

or same proton number1

(atoms with) different number of neutrons

allow different mass number1

(ii) 821

(iii) 1241

7

(b) (i)

1 mark for each correct box3

(ii) (a) neutron1

(iii) 4.0 × 10-4 (s)or0.0004

3.00 × 108 × 0.1 = 12 000 / t

gains 1 mark2

(iv) particles need to travel a large distance1

equipment would have to be very long1

with circular paths long distances can be accommodated in a smaller space1

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(c) (i) the average time for the number of nuclei to halve1

the time for count rate to halve1

(ii)

1 mark if top boxes total = 265

and bottom boxes total = 108

1 mark for 4 and 2 for alpha2

(d) (i) 3 plotted points

± ½ small square1

best line through points1

(ii) 190−205 (pm)or correct from student’s line

1

[20]

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(a) (same) number of protons

same atomic number is insufficient1

(b) (i) nuclei split

do not accept atom for nuclei / nucleus1

(ii) (nuclear) reactor1

(c) beta1

any one from:• atomic / proton number increases (by 1)

accept atomic / proton number changes by 1• number of neutrons decreases / changes by 1• mass number does not change

(total) number of protons and neutrons does not change• a neutron becomes a proton

1

(d) (average) time taken for number of nuclei to halveor(average) time taken for count-rate / activity to halve

1

(e) (i) 6.2 (days)

Accept 6.2 to 6.3 inclusiveallow 1 mark for correctly calculating number remaining as 20 000orallow 1 mark for number of80 000 plus correct use of the graph (gives an answer of 0.8 days)

2

(ii) radiation causes ionisation

allow radiation can be ionising1

that may then harm / kill healthy cells

accept specific examples of harm, eg alter DNA / cause cancer1

(iii) benefit (of diagnosis / treatment) greater than risk (of radiation)

accept may be the only procedure available1

[11]

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(a) a uranium nucleus1

absorbs a neutron1

(uranium-236 nucleus) splits into two smaller nucleiorKr and Ba nucleiorkrypton and barium nuclei

1

and releases 3 neutrons and energy1

9

(b) light nuclei1

join to form a heavier nucleus

allow hydrogen nuclei for light nuclei

allow helium nucleus for heavier nucleus1

(some of the) mass of the nuclei is converted to energy

allow particles for nuclei1

(c) any two from:

• easy to obtain / extract• available in (very) large amounts• releases more energy (per kg)

do not accept figures only

naturally occurring is insufficient

seawater is renewable is insufficient

less cost is insufficient

allow produces little / no radioactive waste2

[9]

(a) Nucleus splitting into two fragments and releasing two or three neutrons110

(at least one) fission neutron shown to be absorbed by additional large nucleus andcausing fission

1

two or three additional neutrons released from fission reaction1

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This diagram would gain all 3 marks:

(b) lowering the control rods increases the number of neutrons absorbed

accept converse description1

(so) energy released decreases1

allow changing the position of the control rods affects the number ofneutrons absorbed for 1 mark

(c) rate of increase between 240 and 276 (MW / min)2

allow 1 mark for attempt to calculate gradient of line at 10 minutes

[7]

(a) any three from:

• no carbon dioxide emitted (to produce electricity)

no greenhouse gases is insufficient

• doesn’t cause global warmingallow climate change or greenhouse effect for global warming

• nuclear power doesn’t cause earthquakes• more energy released per kg of fuel (compared to shale gas)

3

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(b) uraniumorplutonium

ignore any numbers given1

(c) a neutron is absorbed by a (large) nucleus

a description in terms of only atoms negates first two marking points1

the nucleus splits into two (smaller) nuclei1

releasing energy (and gamma rays)1

and (two / three) neutrons1

[8]

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(a) smoke absorbs / stops alpha radiationallow alpha particles for alpha radiation

alpha radiation does not reach the detector is insufficient1

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(b) alpha radiation is not very penetratingallow alpha particles for alpha radiation

oralpha radiation does not penetrate skin

allow alpha radiation does not travel very far (in air)1

(c) beta and gamma radiation will penetrate smokeallow beta and gamma radiation will not be stopped by smoke

1

no change (in the count rate) would be detected

allow the change detected (in the count rate) would be too small1

(d) (a long half-life means) the count rate is (approximately) constantallow activity of source is (approximately) constant

ora short half-life means the count rate decreases quickly

1

until 1.3 half-lives the count rate is above 80 per second

allow after 1.3 half-lives the count rate is below 80 per second

oruntil 1.3 half-lives the count rate is above the threshold for the smoke alarm to beactivated

orafter 1.3 half-lives the smoke alarm will be activated all the time

so don’t have to replace source or smoke detector is insufficient1

(e) Level 2: Relevant points (reasons / causes) are identified, given in detail and logicallylinked to form a clear account.

3−4

Level 1: Relevant points (reasons / causes) are identified, and there are attempts atlogically linking. The resulting account is not fully clear.

1−2

No relevant content0

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Indicative content

• short half-life or half-life of a few hours• (short half-life means) less damage to cells / tissues / organs / body• low ionising power• (low ionising power means) less damage to cells / tissues / organs / body• highly penetrating• (highly penetrating means) it can be detected outside the body• emits gamma radiation

[10]

(a) most alpha particles pass straight through the atom1

which shows that the atom is mostly empty space1

very few alpha particles are deflected through a large angle1

which shows the atom contains a nucleus where the mass / chargeof the atom is concentrated

1

13

(b) electron may absorb electromagnetic radiation

full credit may be scored for a description of an electron emittingelectromagnetic radiation

1

(and) move further from the nucleus1

to a higher energy level1

[7]

(a) cannot predict which dice / atom will ‘decay’

accept answers given in terms of ‘roll a 6’1

14

cannot predict when a dice / atom will ‘decay’1

(b) 3.6 to 3.7 (rolls)

allow 1 mark for attempt to read graph when number of dice = 502

(c) 901

(d) uranium1

(e) beta1

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proton number has gone up (as neutron decays to proton and e–)1

(f) prevents contamination

or

prevents transfer of radioactive material to teacher’s hands1

which would cause damage / irradiation over a longer time period.1

[10]

(a) (i) splitting of a(n atomic) nucleus

do not accept splitting an atom1

(ii) Neutron1

15

(b) (i) nuclei have the same chargeornuclei are positive

accept protons have the same charge1

(ii) (main sequence) star

accept Sun or any correctly named star

accept red (super) giant1

(c) (i) any two from:• easy to obtain / extract• available in (very) large amounts• releases more energy (per kg)

do not accept figures only• produces little / no radioactive waste.

naturally occurring is insufficient

seawater is renewable is insufficient

less cost is insufficient2

(ii) any one from:• makes another source of energy available• increases supply of electricity• able to meet global demand• less environmental damage• reduces amount of other fuels used.

accept any sensible suggestion

accept a specific example

accept a specific example1

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(d) 12

allow 1 mark for obtaining 3 half-lives2

[9]

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Examiner reports

A very small number of the students scored all 4 marks, and a majority of the students scoredzero. A major problem was again a lack of clear description or a failure to read the questioncarefully which resulted in a description of one or the other models without reference todifferences.

1

(a) About two-thirds of students were able to gain at least one of the three marks, but fewscored all three marks.

(b) Just under half of the students gained both marks, with a small number gaining one markfor correctly marking the graph, but misreading the value from the time axis.

(c) A small number of responses gained at least one of the marks, even less scoring bothmarks. There was little indication that students understood the concept of a radioactivetracer, at least in the given context.

2

(a) A majority of students scored this mark.

(b) Again, a majority of students scored this mark.

(c) (i) Over half of students scored zero, the most common error being an attempt tochange mass and proton numbers in accordance with alpha decay. Students who gotthe proton number correct almost always scored full marks. The most commonmistake made with the mass number was subtracting 1 rather than adding 1.

(ii) Under half of students correctly answered this for both marks. A minority of studentsscored one mark for correctly identifying four half-lives sufficiently well to gain credit.The most common mistake amongst students scoring one mark was to neglect tomultiply 4 by 8, leaving 4 as the answer. Of the students who failed to score anymarks 1200/75 to give 16 days was one common misconception, another was incounting five half-lives, i.e. 1200 as 1 half-life, 600 as 2 half-lives etc. resulting in ananswer of 40. A disappointing number of students could not multiply 4 × 8 correctly,giving answers of 24 or 36.

(iii) Only 10% of students scored both marks for this question. Some students scored onemark for correctly stating that the tablets inhibit the absorption of I-131 but not statingthe link to a reduced chance of developing cancer. Some students scored one markfor indicating that the tablets did reduce the chance of developing cancer but withincorrect reasoning. Two common misconceptions were that the tablet acted like avaccination to prepare the body to deal with the radioactive iodine using anti-bodies,or that the non-radioactive iodine would in some way neutralise the radioactivity ofI-131.

3

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(a) (i) Nearly all students were able to determine the value of background count from atable listing values of count rate and corrected count rate.

(ii) Only half of the students stated that corrected count is the count rate due to thesource.

(iii) Well over half of the students knew that the data given in the table was not related toan alpha source. Some stated that it could not be an alpha source because thereadings of count rate were not high enough. Others backed up their correct answerswith realistic ranges for alpha particles.

(iv) The standard of graph plotting was very high and more than two thirds of studentsscored full marks for accurate plotting and drawing a curve through the points.

4

(v) Students were introduced to the idea of half-distance and were asked to statewhether a constant value of half distance could be seen from the data given in thetable. Some very good answers were seen with over a third of students scoring allthree marks.

There was conflicting evidence in the table and students were expected to make ajudgement on the data that they used. Many students were stuck with the idea ofhalf-life and used this term throughout.

A common error was ‘if the count rate did not halve when the distance doubled, thenthe hypothesis was invalid’. Here the doubling of distance is irrelevant; it is thechange in distance that matters. Many students used the change in distance of 0.4 mresulting in the count rate halving from 20 to 10 as the basis of a successful answer.

Many students gave up immediately because 56 was not half of 125.

(b) (i) This question scored very poorly, with very few students able to describe the effect ofa magnetic field on a beam of beta particles. Many thought that the magnetic fieldblocked the particles or that the particles went off in the direction of the field or werereflected backwards by the field. There were many loose statements such as ‘whenthe magnetic field travels towards the detector’.

(ii) Hardly any students realised that the readings were due to background count. Theyoften gave long explanations as to why the three readings were different includingthat in experiment 1 the magnetic field repels the particles back towards the source.

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(a) (i) Surprisingly only just over half of students gained this mark, with the popular answersbeing ‘nuclear power stations’ or ‘nuclear weapons testing’. ‘X-Rays’ was also acommon response. The common incorrect responses were smoke detectors andvague answers referring to medical uses without being specific. A significant numberof students failed to see that ‘man-made sources’ was in bold and responded with‘cosmic rays’ and ‘rocks’.

(ii) Several students gave the correct response in terms of background radiation varyingbut relatively few gave the answer in terms of decay being a random process.Common incorrect answers referred to the teacher moving the experiment around thelab to cause the differences or to other radioactive sources being present at the timesof the three readings, including the introduction of radioactive materials into the roomand the presence of different food being present when the readings were taken.Many did use ‘vary’ or ‘changes’ but too many gave responses showing a completelack of understanding of this process.

(b) The most common correct response was ‘other factors’. When other factors werementioned, it was usually smoking. Several students gave answers referring to thehereditary aspect of cancer. Very few answers talked about the validity of the evidence, orthe sample size.

(c) The majority of the students gained both marks.

(d) Almost two thirds of the students gave the correct response of 3.8 days, with a few givingthe answer as a fraction and one or two converting 0.8 days into hours and minutes. Nearlyall correct answers used the counts of 800 and 400 to determine the half-life. A fewmisread the x axis scale and then answered 3.4 days and a few, after drawing correct linesthen put down an incorrect answer. Common errors included believing the “222” of radonwas important and so a line was drawn across from a count of 222 to give a half-life near 7days.

5

(a) (i) Nearly two thirds of students scored this mark with the main incorrect answer beinguranium; a very few candidates gave thorium instead of plutonium.

(ii) Despite the instruction to the contrary, too many students simply described thefission process. Marks scored tended to be 0 or 3. A significant minority of studentsdid not attempt the question. The most common error in the good attempts tended tobe to replace the turbine with the generator, although propellers and rotators werealso erroneously mentioned. Those students who answered successfullydemonstrated a clear and detailed knowledge of the process, by describing the wholeprocess, including the turbine driving the generator.

(b) The students who knew how to approach this diagram did well. Unfortunately a significantminority of students did not even attempt the diagram. The most frequent error wasshowing the process as continuing from the two daughter nuclei shown. Often candidatesseemed to have an idea of the process but either failed to show it clearly, or did not uselabels to support poor diagrams.

(c) Most students who scored at least one mark did so by knowing neutrons were absorbed bythe boron, although they often failed to make this absolutely clear. The descriptions for thethird marking point too often failed to earn credit, by simply writing as a result “less energyreleased”.

6

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(a) (i) Two thirds of students scored both marks. Those failing to score often confusedwhich particle had the same number and which had different numbers or includedincorrect references to electrons but more commonly referred to ‘elements’ ratherthan ‘an element’ or ‘atoms’. Few students scored the marks by referring to atomicnumber and mass number.

(ii) Nine tenths of students gained the mark on this question for identifying the atomicnumber.

(iii) Similarly, nine tenths of students gained the mark on this question for correctlycalculating the number of neutrons.

(b) (i) More than half of students gained all three marks here. Poor arithmetic was as muchto blame as poor understanding for those who made mistakes.

(ii) Three-quarters of students correctly identified the neutron. Incorrect answers includedelectron, proton, hydrogen, uranium and gamma.

(iii) Half of students gained both marks, but nearly as many scored zero. The mostcommon mistake was to not recognise the speed of the iron nuclei as one-tenth thespeed of light resulting in their answer being incorrect by a factor of ten. Omitting the0.1 gave a value of 0.00004 but often seen was some other power of 10 error -possibly due to calculator misuse. Occasionally students rearranged incorrectly andgot a value of 2500. The use of standard form was not as common as hoped;approximately half the correct answers were not in standard form and many partiallycorrect answers were expressed as a fraction.

(iv) Three fifths of students scored zero marks on this question. Very few realised that alinear accelerator would need to be very long, while a circular accelerator could bebuilt in a smaller space. Some students described acceleration in a circle andcentripetal forces. Many students clearly did not understand what the question wasasking.

(c) (i) Nearly all students gained at least one mark and three-quarters gained both. Somestudents failed to tick two boxes.

(ii) Two thirds of students gained both marks. Most students realised that the combinedmass numbers and proton number should total 265 / 108. There were often unusualmass and atomic numbers written for the alpha particle; 0 & -1 were often seen, butalso numbers containing figures to the right of a decimal point and numbers greaterthan 4.

(d) (i) Two thirds of students scored both marks for correct plotting and a suitable line ofbest fit. Only a small number of students did not draw a straight line. Some straightlines were drawn to far from the data and so did not score a mark. Mis-plotting couldlead the student to draw a curve and these were accepted if they were drawn well.

(ii) Nine tenths of students gained the mark for correctly extrapolating the line andestimating a suitable number.

7

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(a) Nearly three fifths of the students gave the correct answer, ‘number of protons’. Many ofthe students did not understand the term ‘in common’ and instead, wrote about thedifferences between isotopes.

(b) (i) About two fifths of the students correctly stated that nuclei are split in nuclear fission.Most of the remaining students had an idea of what happens but used ambiguousand vague terminology, using ‘break apart’, ‘divide’ ‘particles’ without supportingexplanation and thus lacked sufficient clarity to obtain the mark.

(ii) A lack of clarity again stopped students obtaining this mark with only about two fifthsnaming the reactor as the part where molybdenum is produced.

(c) About two thirds of the students identified the radiation as beta. However the reasons givenwere often confused, imprecise and sometimes contradictory. Examples seen include:‘atomic number stays the same but number of protons goes up’, ‘nucleus loses a protonand gains a neutron’, ‘nucleus loses a neutron but gains a proton and an electron’, etc.Less than a third of the students gave complete answers that correctly gave the markingpoints in the mark scheme.

(d) Only less than a third of the students gave answers sufficient to score the mark. A smallproportion of the students gave an answer in terms of the count rate halving.

(e) (i) About two thirds of the students recognised that the number remaining was 20,000but then less than half of these students used the graph to correctly identify 6.2-6.3days as the time required. A small amount of students drew lines on the graph at80,000 and identified 0.8 days but half of them, then carried out further calculationson this and consequently lost the compensation mark.

(ii) Fewer than a third of the students scored the mark for the ionising effect of radiation;of those who did, they usually went on to score the second mark. Most of thestudents that scored the second mark did so for general terms about radiation‘causing cancer’ or some form of harm. Few students linked the ionising effect ofradiation to damage or harm to individual cells or DNA.

(iii) Many of the students reiterated statements from part e(ii) about the dangers ofradiation rather than answering the question asked. Students’ phrasing of theirresponse was often confused with only about a fifth being able to describe that thebenefits outweighed the risks.

8

(a) 11% of students scored 3 marks, 27% of students scored 2 marks. Lots of thoroughanswers were seen, but they needed to state the advantages of nuclear, rather thandisadvantages of shale gas. ‘Shale gas releases CO 2’ did not score a mark, but ‘nucleardoes not release CO2’ did score a mark. Information about shale gas was given in thequestion, which is why these answers were insufficient for a mark.

11

(b) 66% answered this question correctly. The most common correct answer was uranium. Acommon incorrect answer seen was oil.

(c) Many good answers seen with 12% scoring 4 marks and 20% scoring 3 marks. Somestudents didn’t mention the nucleus absorbing the neutron or the nucleus splitting in two, sothey didn’t score the first two marking points. The first marking point was the least likely toscore. The third marking point was scored by most students.

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(a) 57% of students scored 2 marks for this question, with 32% scoring 1 mark. The mostcommon mistake was not stating which quantity should remain constant, ‘charge’ being acommonly seen incorrect answer.

12

(b) 74% of students scored a mark for this question, usually for the idea of low penetratingability. ‘Doesn’t penetrate skin’ was creditworthy, ‘doesn’t penetrate paper’ was insufficient.‘Doesn’t penetrate the case’ was allowed.

(c) 53% of students scored 1 mark for this question but very few scored 2 marks. Moststudents answered in terms of beta and gamma radiation being able to penetrate thesmoke, but didn’t link this idea to the need for a change in the radiation reaching thedetector for the alarm to sound.

(d) Very few 2 mark answers were seen. Most students scored zero, with insufficientresponses having to do with saving money, or not having to replace the source very often.Very few linked the graph to the question, and realised that 1.3 half-lives could be anyamount of time depending on the radioisotope used.

(e) Well answered by many students, 36% scoring 3 or 4 marks. Those who didn’t usually gaveopposite statements to the ideal properties, such as low penetrating ability but highlyionising, which will have limited their overall score. The minimum required for a 4 markanswer would have been two properties with explanations, or four simple statements. Manystudents gave much fuller answers than this, however.

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(a) (i) Less than half of the students scored this mark. The most common error was to usecolloquial terminology of ‘splitting the atom’ rather than referring to the nucleus.

(ii) Just fewer than half of the students named the particle as a neutron to score thismark. Common errors were ‘alpha particles’ or ‘Uranium 235’.

(b) (i) Although this was quite accessible, many of the students simply quoted a rule like‘like charges repel’ without relating their answer to nuclei. Others did not interpret thequestion properly and attempted to explain about forces within the nucleus orbetween the nucleus and electrons. About half of the students scored this mark.

(ii) This question was better answered with most of the students scoring the mark. Thestudents that failed to score the mark either gave far too general answers like ‘inspace’ or focussed on other contexts − both biological and geological − withreferences to fertilisation and to volcanoes.

(c) (i) Many students had a good attempt at this question with almost half of the studentsscoring one mark and a further third scoring both. Many students gave an economicargument which was not creditworthy.

(ii) This was poorly answered. Correct answers were not common, but referrals toreducing reliability on other fuel sources and reducing environmental damage werethe most frequent. In suggesting an important consequence of developing fusiontechnology, many students expressed concern over the release of radioactivematerial, meltdown and references to the reactors running out of control. Incorrectresponses like ‘difficult to dispose of the radioactive waste’ or ‘lots of carbon dioxideemissions’ were common.

(d) Of those students that did attempt an approach which resembled a half-life calculation,those that identified there were three half-lives were awarded one mark and in most casesthese students went on to correctly calculate the answer and score both marks. There werea significant number of students who identified the sequence 80-40-20-10 and thenincorrectly thought this made four half-lives and another group that divided into 36 years toarrive at an answer of 4.5 years. Only one third of the students scored both marks.

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name: atomic structure - aston academy gcse physics€¦ · against atomic number and draw a line...

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