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International A LevelPhysicsEdexcelExam Questions5. Thermodynamics, Radiation, Oscillations & CosmologyRadioactivity Decay

Radioactivity Decay (Edexcel International A Level Physics)

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Radioactivity Decay

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Radioactivity Decay

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1a
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Cobalt‐60 is a source of gamma radiation. Gamma radiation can be used to sterilise medical equipment.

i) Complete the nuclear equation for the decay of cobalt-60 to nickel.

    Co presubscript 27 presuperscript 60 space rightwards arrow space Ni presubscript midline horizontal ellipsis midline horizontal ellipsis end presubscript presuperscript midline horizontal ellipsis midline horizontal ellipsis end presuperscript space plus space straight beta presubscript midline horizontal ellipsis midline horizontal ellipsis end presubscript presuperscript midline horizontal ellipsis midline horizontal ellipsis end presuperscript superscript minus space plus space scriptbase straight v with bar on top end scriptbase presubscript 0 presuperscript 0 subscript straight e

(2)

ii) Suggest why the majority of the energy released is shared between the β− particle and the antineutrino.

(1)

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1b
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The activity of a cobalt‐60 source is 4.07 × 1014 Bq initially.

When used for sterilising, the source is replaced when the activity drops below 1.85 × 1014 Bq.

Calculate the time in years until the source should be replaced.   

half-life of cobalt‐60 = 5.27 years    

1 year = 3.16 × 107 s

Time until source should be replaced = .........................years

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1c
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When in use the cobalt-60 source is shielded with lead. The graph shows how the transmission of γ-radiation depends upon the thickness x of the lead shielding.

q19c-wph15-05-oct-2021-edexcel-int-as-and-a-level-phy

The count rate from a source must be reduced from 4.0 × 1014 Bq to 1.2 × 1014 Bq.

Deduce whether lead shielding of thickness 1.0 cm would be sufficient to achieve this.

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2a
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A pacemaker is a device used to regulate a person’s heart rate.

Some of the first electronic pacemakers used an isotope of plutonium, Pu-238, as the power source.

Pu-238 decays by alpha emission.

Show that the energy released when a nucleus of Pu-238 decays into a nucleus of uranium is about 5.6 MeV.

Mass/u

Plutonium nucleus

237.999089

Uranium nucleus

233.991578

α-particle

4.001506

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2b
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Another source that was used in early pacemakers was promethium-147. This emits β-particles. The energy spectrum for the β-particles is shown.

q19c-wph15-05-june-2021-edexcel-int-as-and-a-level-phy

The graphs below show how the range of beta particles depends on the beta particle energy, for different materials.

q19c-1-wph15-05-june-2021-edexcel-int-as-and-a-level-phy

It is suggested that a layer of polyethylene, of thickness 0.5 cm, would be able to absorb all the beta particles emitted from a promethium-147 source.

Comment on this suggestion.

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1
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Strontium-90 is commonly used in schools to demonstrate the properties of β particles.

The range of energies of β particles emitted from a source of strontium-90 is shown below.

q14-wph15-05-jan-2022-edexcel-int-as-a-level-phy

When β particles travel through air they ionise air molecules, which limits how far they travel. The range of the β particles depends upon their kinetic energy when released from the nucleus.

The graph below shows how the range of a β particle in air depends upon its kinetic energy.

q14-1-wph15-05-jan-2022-edexcel-int-as-a-level-phy

It is estimated that the most energetic β particles from strontium-90 will ionise 250 nitrogen molecules per cm of air that they pass through.

15.6 eV is required to ionise a nitrogen molecule.

Assess whether this estimate is consistent with the range of these β particles in air.

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2
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A pacemaker is a device used to regulate a person’s heart rate.

Some of the first electronic pacemakers used an isotope of plutonium, Pu-238, as the power source.

In one pacemaker, the activity of the plutonium source was measured to be 6.75 × 1010 Bq in 2020.

Calculate the power of the source, in W, when it was fitted 40 years ago.    

half-life of Pu-238 = 87.7 years    

energy of α-particle = 5.6 MeV

Power of source = ......................................... W

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