Radioactivity (Cambridge (CIE) IGCSE Physics)

The isotope hydrogen-1 has a proton number of 1 and a nucleon number of 1.

  Two isotopes of helium are helium-3 and helium-4.

  Helium-3 has a proton number of 2 and a nucleon number of 3.

  Helium-4 has a nucleon number of 4.

 Complete Table 11.1 for neutral atoms of these isotopes of helium.

Table 11.1

An experiment takes place in a laboratory shielded from all background radiation. A sample of radioactive material is wrapped in aluminium foil of thickness 0.1 mm. A detector of ionising radiation placed 1 cm from the foil records a reading.

A piece of aluminium of thickness 5 mm is placed between the detector and the foil. The detector reading drops to zero.

  State and explain any type of radiation passing through the aluminium foil.

This notation represents the nucleus of a neutral atom of carbon-14.

State the number of:

(i) protons in the nucleus of an atom of carbon-14

[1]

(ii) electrons orbiting the nucleus of an atom of carbon-14

[1]

(iii) neutrons in the nucleus of an atom of carbon-14.

[1]

Carbon-14 is an isotope of carbon. Carbon-12 is another isotope of carbon.

  Compare the nucleus of carbon-14 with the nucleus of carbon-12.

   State the similarities and differences.

Scientists use carbon-14 to estimate the age of wood that is very old.

A very old sample of wood contains 1.0 × 10⁸ carbon-14 atoms.

 When the sample was new, it contained 8.0 × 10⁸ carbon-14 atoms. The half-life of carbon-14 is 5700 years.

Estimate the age of the sample of wood.

age of wood = ........................... years

Radioactive sources emit α-(alpha), β-(beta) and γ-(gamma) radiations.

State which of these types of radiation can pass through paper.

Barium-137 is a radioactive isotope. The nuclide notation for barium-137 is

Determine the number of neutrons in a nucleus of barium-137.

number of neutrons = ........................................................

An isotope of barium–137 has a half-life of 3 minutes.

A radioactive source contains 36 mg of this isotope.

Calculate the mass of the isotope that remains in the source after 9 minutes.

 mass of the isotope remaining = .................................................. mg

Fig. 10.1 shows a vacuum tube with a radioactive source. The radioactive source emits α-particles, β-particles and γ -rays. There is a very strong magnetic field between the N pole and the S pole of the magnet.

The lead cylinder has a narrow central hole. State and explain the effect of the lead cylinder.

Extended tier only

Describe the paths of the α-particles, β-particles and γ -rays as they pass through the magnetic field. Explain your answers.

 (i) α-particles

[2]

(ii) β-particles

[2]

(iii) γ -rays

[2]

Radioactive decay may include the emission of:

α-radiation

β-radiation

γ-radiation

(i) From the list, state the type of radiation which has the greatest ionising effect.

[1]

(ii) From the list, state the type of radiation which has the lowest penetrating ability.

[1]

Extended tier only

In a factory, rollers press aluminium metal to make thin foil sheets. An automatic system for controlling the thickness of the foil uses a radioactive source. The automatic system changes the gap between the top and bottom roller. Fig. 12.1 shows the equipment.

(i) Use your ideas about the properties of radiation to suggest and explain the type of radiation used.

 type of radiation: ..........................................................................................

explanation: ..........................................................................................

[2]

(ii) The aluminium foil passing the radiation detector is too thin. Describe how this fault affects the reading on the counter.

[1]

(iii) Suggest how the fault in (b)(ii) is corrected. State what happens to the rollers.

[1]

(iv) The source used is strontium-90. A nucleus of strontium-90 can be described as . State the number of protons in a nucleus of strontium-90.

[1]

Radon-222 is radioactive. It can be represented as .

For a neutral atom of radon-222, state

1. the number of protons, ...........................

2. the number of neutrons, ...........................

3. the number of electrons. ...........................

Extended tier only

A radon-222 nucleus decays by α-particle emission to a polonium (Po) nucleus.

Complete the equation for the decay of radon-222.

Radon-222 has a half-life of 3.8 days.

At a certain time, a sample contains 6.4 × 10⁶ radon nuclei.

Calculate the number of α-particles emitted by the radon nuclei in the following 7.6 days.

number = ...........................................................

The nuclide notation describes the nucleus of one type of atom. Draw a line from each symbol to the correct description for that symbol.

(i) One radioactive isotope has a half-life of 6.0 years.

A sample of this isotope has a mass of 12 mg.

Calculate the mass of this isotope that remains in the sample after 18 years.

mass remaining = .................................................... mg [3]

(ii) The sample decays by emitting a β-particle.

Describe the nature of a β-particle.

 [2]

(iii) Describe how the nucleus of the isotope changes due to the emission of a β-particle.

 [1]

Extended tier only

A radioactive nucleus of uranium-235 decays to a nucleus of thorium and emits an α-particle. Complete the equation.

A nucleus of uranium-235 undergoes nuclear fission in a reactor.

(i) State what is meant by nuclear fission.

[1]

(ii) Suggest why a nuclear reactor is surrounded by thick concrete walls.

[2]

(iii) State one environmental advantage and one environmental disadvantage of using a fission reactor to generate electrical energy in a power station.

[2]

The thorium produced by the decay in (a) is also radioactive and has a half-life of 26 hours.

At a certain time, a pure sample of this isotope initially contains 4.8 × 10⁹ atoms.

Calculate the number of atoms of this sample that decay in the following 52 hours.

number = ...........................................................

Extended tier only

A radioactive nucleus of carbon decays to a nucleus of nitrogen by emitting a particle.

 Complete the nuclide equation and state the name of the particle.

Extended tier only

A radiation detector in a laboratory records a reading of 10 counts/min. There are no radioactive samples in the laboratory.

(i) Explain why the radiation detector records a reading and suggest a possible source.

[2]

(ii) Carbon-14 has a half-life of 5700 years. There are atoms of carbon-14 in all living organisms.

 An archaeologist digs up some ancient wood. In the same laboratory as in (b)(i), a sample of this ancient wood gives a reading of 20 counts/min. An equivalent sample of living wood gives a reading of 80 counts/min. It is suggested that the age of the ancient sample is 11 400 years.

 Do a calculation to check whether this suggestion is correct.

[4]

Fig.12.1 shows a radioactive source placed close to a radiation detector and counter. The detector can detect α, β and γ radiation.

The radioactive source emits β-particles only.

  Describe how you could show that the source emits β-particles only. As part of your answer, you may draw on Fig.12.1 and add any other apparatus you may need.

A teacher carries out two experiments at the same time.

In the first experiment the count rate for a sample of a radioactive isotope is measured every 30 seconds for 6 minutes.

The results are shown in Table 12.1.

Table 12.1

Estimate the half-life of the radioactive isotope. Use the information in the table.

half-life = ...................................................... minutes 

In the second experiment the teacher repeats the procedure with another sample of the same radioactive isotope. The mass of the second sample is greater than that of the first sample.

  Suggest a value for the count rate for this sample at the start of the experiment.

count rate = ...................................................... counts/second

One type of particle emitted during radioactive decay is an α-particle (alpha particle).

Describe:

(i) the nature of an α-particle

[1]

(ii) the ionising ability of an α-particle

[1]

(iii) the penetrating ability of an α-particle.

[1]

A radioactive substance decays by emitting an α-particle.

The nuclide notation for an α-particle is

(i) State the term given to the number 4, written in the nuclide notation.

[1]

(ii) State the term given to the number 2, written in the nuclide notation.

[1]

Fig. 12.1 shows the decay curve for a radioactive material.

(i) Use information from the graph in Fig. 12.1 to determine the half-life of the material. Clearly show how you used the graph to obtain your answer.

 half-life = ...................................................... minutes [3]

(ii) Another radioactive material with the same half-life has an initial count rate of 600 counts/min. On Fig. 12.1 sketch the decay curve for this material.

[1]

Astatine-210 is a radioactive material. The nucleus of astatine can be represented by the symbol shown.

Complete the table to describe the nucleus of astatine-210.

Astatine-210 has a half-life of 8 hours. 

(i) The count rate of a sample of astatine-210 is measured over 24 hours.

 On Fig. 12.1, sketch a line to show how the count rate changes over the 24 hours.

[2]

(ii) The mass of a sample of astatine-210 is 0.500 kg.

Calculate how long it takes for 0.375 kg of the sample to decay.

decay time = ............................................... hours [3]

State the type of radioactive emission that causes

(i) the proton number of a nuclide to increase by 1,

[1]

(ii) the nucleon number of a nuclide to decrease by 4,

[1]

(iii) no change in the proton number and no change in the nucleon number of a nuclide.

[1]

Extended tier only

The isotope radon-220 is radioactive and it decays by α-particle emission.

(i) Fig. 11.1 shows a beam of α-particles entering the electric field between two charged plates.

On Fig. 11.1, sketch the path that the beam of α-particles follows in the electric field.

[1]

(ii) The half-life of radon-220 is 56 s.

A sample of this isotope contains 7.2 × 10⁶ atoms.

Predict the number of α-particles that the radon-220 in the sample emits in the next 168 s.

number of α-particles emitted = ...........................................................[3]