8.2 Nuclear Physics - Alpha, Beta, Gamma radiation - Qs 8.2 Nuclear Physics - Alpha, Beta, Gamma...

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Transcript of 8.2 Nuclear Physics - Alpha, Beta, Gamma radiation - Qs 8.2 Nuclear Physics - Alpha, Beta, Gamma...

  • Page 1 of 26

    8.2 Nuclear Physics - Alpha, Beta, Gamma radiation – Questions

    Q1. (a) Which ionizing radiation produces the greatest number of ion pairs per mm in air?

    Tick (✓) the correct answer.

    α particles

    β particles

    γ rays

    X−rays

    (1)

    (b) (i) Complete the table showing the typical maximum range in air for α and β particles.

    Type of radiation Typical range in air / m

    α

    β (2)

    (ii) γ rays have a range of at least 1 km in air. However, a γ ray detector placed 0.5 m from a γ ray source detects a noticeably smaller count-rate as it is moved a few centimetres further away from the source.

    Explain this observation.

    ______________________________________________________________

    ______________________________________________________________

    ______________________________________________________________ (1)

    (c) Following an accident, a room is contaminated with dust containing americium which is an α−emitter.

    Explain the most hazardous aspect of the presence of this dust to an unprotected human entering the room.

    ___________________________________________________________________

    ___________________________________________________________________

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    ___________________________________________________________________

    ___________________________________________________________________ (2)

    (Total 6 marks)

    Q2. A radioactive nucleus decays with the emission of an alpha particle and a gamma-ray photon.

    (a) Describe the changes that occur in the proton number and the nucleon number of the nucleus.

    proton number ______________________________________________________

    nucleon number _____________________________________________________ (2)

    (b) Comment on the relative penetrating powers of the two types of ionizing radiation.

    ___________________________________________________________________

    ___________________________________________________________________ (1)

    (c) Gamma rays from a point source are travelling towards a detector. The distance from the source to the detector is changed from 1.0 m to 3.0 m.

    Calculate

    intensity of radiation at 3.0 m

    intensity of radiation at 1.0 m

    answer ____________________ (2)

    (Total 5 marks)

    Q3. A freshly prepared radioactive source that emits negatively charged beta particles (β–) has an activity of 120 Bq and a half-life of 12 h.

    (a) (i) State the effect on the proton number Z and the nucleon number A when a β– particle is emitted.

    ______________________________________________________________

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    ______________________________________________________________ (2)

    (ii) Sketch, on the axes below, a graph that shows how the activity varies during the two days after the source was prepared.

    (3)

    (b) (i) The total energy released in each decay is 5.5 × 10–13 J. Calculate the initial energy produced each second by the source.

    initial energy ____________________ J (1)

    (ii) Figure 1 shows the energy spectrum for the beta particles emitted in the decay.

    It shows that different energy beta particles are possible.

    Figure 1

  • Page 4 of 26

    Explain why all the beta particles that are emitted do not have 5.5 × 10–13 J of energy.

    ______________________________________________________________

    ______________________________________________________________

    ______________________________________________________________

    ______________________________________________________________

    ______________________________________________________________ (3)

    (c) The probability of one of the radioactive atoms decaying each second is 1.6 × 10–5.

    How many radioactive atoms are present when the activity is 120 Bq?

    number of radioactive atoms ____________________ (1)

    (d) A scientist undertaking an investigation places the freshly prepared source close to a Geiger-Müller tube as shown in Figure 2 and records a count rate of 50 counts per second.

    Figure 2

    State and explain two reasons why the measured count rate is lower than the activity of the source.

    ___________________________________________________________________

    ___________________________________________________________________

    ___________________________________________________________________

    ___________________________________________________________________ (2)

    (Total 12 marks)

    Q4. A radium-288 nuclide ( ) is radioactive and decays by the emission of a β– particle to form an isotope of actinium (Ac).

  • Page 5 of 26

    (a) Complete the equation for this decay.

    (3)

    (b) β– decay is the result of a neutron within a nucleus decaying into a proton. Describe the change in the quark sub-structure that occurs during the decay.

    ___________________________________________________________________

    ___________________________________________________________________

    ___________________________________________________________________ (1)

    (Total 4 marks)

    Q5. Iodine-123 is a radioisotope used medically as a tracer to monitor thyroid and kidney functions. The decay of an iodine-123 nucleus produces a gamma ray which, when emitted from inside the body of a patient, can be detected externally.

    (a) Why are gamma rays the most suitable type of nuclear radiation for this application?

    ___________________________________________________________________

    ___________________________________________________________________

    ___________________________________________________________________

    ___________________________________________________________________ (2)

    (b) In a laboratory experiment on a sample of iodine-123 the following data were collected.

    time/h 0 4 8 12 16 20 24 28 32

    count-rate /counts s–1 512 410 338 279 217 191 143 119 91

    Why was it unnecessary to correct these values for background radiation?

    ___________________________________________________________________

    ___________________________________________________________________

    ___________________________________________________________________

    ___________________________________________________________________ (2)

    (c) On the axes provided in the diagram below, complete the graph of count-rate against time.

  • Page 6 of 26

    (2)

    (d) Use your graph to find an accurate value for the half-life of iodine-123. Show clearly the method you use.

    Half-life ____________________ (3)

    (e) Give two reasons why radioisotopes with short half-lives are particularly suitable for use as a medical tracer.

    ___________________________________________________________________

    ___________________________________________________________________

    ___________________________________________________________________

    ___________________________________________________________________

    ___________________________________________________________________ (2)

    (Total 11 marks)

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    Q6. A student has access to a radioactive source that decays by emitting alpha, beta and gamma radiation. The student wishes to investigate whether the count rate due to the gamma radiation varies with distance from the source according to an inverse square law and sets up the source and detector as shown in Figure 1.

    (a) State and explain how the student can ensure that only gamma radiation is detected during the investigation.

    ___________________________________________________________________

    ___________________________________________________________________

    ___________________________________________________________________

    ___________________________________________________________________ (2)

    (b) The corrected count rate due to gamma radiation is 64 counts per second at a distance of 50 mm from the source. Assuming that an inverse square law is obeyed calculate the expected corrected count rate at a distance of 80 mm from the source.

    Count rate at 80 mm ____________________ (2)

    (c) Using the data from part (b) sketch, on the axes in Figure 2, the graph the student would expect if an inverse square law were obeyed. The corrected count rate at 50 mm has been plotted already.

  • Page 8 of 26

    Figure 2 (2)

    (Total 6 marks)

    Q7. Thallium (Tl) decays to a stable form of lead (Pb) with the emission of a β– particle. Complete the equation below for this decay.

    (Total 3 marks)

    Q8. (a) (i) Alpha and beta emissions are known as ionising radiations. State and explain

    why such radiations can be described as ionising.

    ______________________________________________________________

    ______________________________________________________________

    ______________________________________________________________

    ______________________________________________________________ (2)