Radioactivity Decay (Edexcel International A Level Physics)

Topic Questions

5 marks

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.

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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.

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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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3 marks

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

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

{}_{27}^{60}{Co} \to {}_{\dots \dots}^{\dots \dots}{Ni} + {}_{\dots \dots}^{\dots \dots}β^{-} + {}_{0}^{0}{\bar{v}}_{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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3 marks

The activity of a cobalt‐60 source is 4.07 × 10¹⁴Bq initially.
When used for sterilising, the source is replaced when the activity drops below 1.85 × 10¹⁴Bq.
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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3 marks

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.

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The count rate from a source must be reduced from 4.0 × 10¹⁴Bq to 1.2 × 10¹⁴Bq.
Deduce whether lead shielding of thickness 1.0 cm would be sufficient to achieve this.

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	Mass/u
Plutonium nucleus	237.999089
Uranium nucleus	233.991578
α-particle	4.001506