View Member-Area

5.2-Radioactivity

Download PDF

IGCSE Physics Notes / Radioactivity

 

5.2 Radioactivity

Summary Fill in the Blanks + Exam Practice

Click the blanks to reveal the key answers. For longer exam-style responses, click the answer buttons to reveal full model answers.

1Detection of Radioactivity

Background radiation is the ionising radiation that is
_______always present
in the environment.
A major source of background radiation is
_______radon gas
in the air.
Other sources include
_______rocks and buildings
,
_______food and drink
and
_______cosmic rays
.
Ionising nuclear radiation can be measured using a
_______detector
connected to a
_______counter
.
Count rate can be measured in
_______counts / s
or
_______counts / minute
.
To find corrected count rate, subtract the
_______background radiation
count from the measured count.

2The Three Types of Nuclear Emission

Radiation from a nucleus is emitted
_______spontaneously
and in a
_______random
direction.
The three types of nuclear emission are
_______alpha
,
_______beta
and
_______gamma
.
Alpha particles are the nuclei of
_______helium
atoms.
Beta particles are
_______fast-moving electrons
.
Gamma rays are
_______electromagnetic waves
.
The most ionising radiation is
_______alpha
.
The least ionising radiation is
_______gamma
.
The least penetrating radiation is
_______alpha
.
The most penetrating radiation is
_______gamma
.
Beta particles are
_______negatively charged
.
In electric and magnetic fields, alpha and beta are
_______deflected
but gamma is
_______not deflected
.

3Radioactive Decay

Radioactive decay is a change in an
_______unstable nucleus
.
It can result in the emission of
_______alpha particles
,
_______beta particles
and / or
_______gamma radiation
.
Radioactive decay is
_______spontaneous
and
_______random
.
During alpha decay or beta decay, the nucleus changes into that of a different
_______element
.
Isotopes may be radioactive because of an excess of
_______neutrons
in the nucleus or because the nucleus is too
_______heavy
.
During beta emission, a
_______neutron
changes into a
_______proton
and an
_______electron
.
Radioactive decay can increase
_______stability
and reduce excess neutrons.

4Half-life

Half-life is the time taken for
_______half the nuclei
in a sample to decay.
Half-life can be calculated from
_______data
or
_______decay curves
.
In simple half-life calculations at this level,
_______background radiation is not included
.
Smoke alarms commonly use a source that emits
_______alpha particles
.
Sterilisation of equipment and cancer treatment commonly use
_______gamma rays
.
Measuring thickness depends on the penetration and
_______absorption
of the radiation used.

5Safety Precautions

Ionising radiation can cause
_______cell death
,
_______mutations
and
_______cancer
.
Radioactive materials must be moved, used and stored
_______safely
.
Exposure to ionising radiation is reduced by decreasing
_______time
, increasing
_______distance
and using
_______shielding
.

Exam Practice – Click to Reveal Answers

Complete the characteristics table for alpha, beta and gamma radiation: electromagnetic wave, least ionising, least penetrating, a helium nucleus, negatively charged.
Click to reveal answer

Electromagnetic wave: gamma

Least ionising: gamma

Least penetrating: alpha

A helium nucleus: alpha

Negatively charged: beta

A sample contains 8.0 × 1012 atoms of a radioactive isotope of plutonium. The half-life is 14 years. Calculate the number of atoms remaining after 28 years.
Click to reveal answer

28 years is 2 half-lives because 28 ÷ 14 = 2.

After one half-life: 8.0 × 1012 ÷ 2 = 4.0 × 1012

After two half-lives: 4.0 × 1012 ÷ 2 = 2.0 × 1012

Answer: 2.0 × 1012 atoms

Suggest and explain two reasons why smoke detectors use an isotope that emits alpha particles rather than an isotope that emits gamma radiation.
Click to reveal answer

Reason 1: Alpha particles are highly ionising, so they ionise the air easily.

Reason 2: Alpha particles have a short range / low penetrating ability, so they are stopped by smoke particles.

Reason 3: Because alpha is not very penetrating, it is less harmful outside the detector than gamma radiation.

Any two well-explained points score.

In the alpha-particle scattering experiment, alpha particles were directed at a thin gold foil. State what may be inferred from:
(i) most alpha particles pass through the foil
(ii) some alpha particles are scattered through angles greater than 90°.
Click to reveal answer

(i) Most of the atom is empty space, or the nucleus is very small compared with the atom.

(ii) The nucleus is positively charged, and most of the mass of the atom is concentrated in the nucleus.

State the changes in the nucleus during beta emission.
Click to reveal answer

During beta emission, a neutron changes into a proton and an electron.

The electron is emitted as the beta particle.

Explain how safety precautions reduce danger when handling radioactive sources.
Click to reveal answer

Reduce time: less time near the source means less radiation absorbed.

Increase distance: being further from the source reduces exposure.

Use shielding: absorbing materials such as lead or thick concrete reduce the radiation reaching the body.

Exam Summary

Background radiation comes from radon gas, rocks, buildings, food, drink and cosmic rays.

Alpha is most ionising and least penetrating. Gamma is least ionising and most penetrating.

Radioactive decay is spontaneous and random.

Half-life is the time taken for half the nuclei in a sample to decay.

Radiation safety depends on minimising time, maximising distance and using shielding.

Members Area

Unlock the complete range of solved past exam papers along with mock exams, revision notes, timed quizzes, interactive flipbooks and many more exam preparation resources.

Unlock Complete Resources

 

Syllabus Objectives

5.2.1 Detection of radioactivity

CORE OBJECTIVES:

  • Know what is meant by background radiation
  • Know the sources that make a significant contribution to background radiation including:
  • (a) radon gas (in the air)
  • (b) rocks and buildings
  • (c) food and drink
  • (d) cosmic rays
  •  Know that ionising nuclear radiation can be measured using a detector connected to a counter
  •  Use count rate measured in counts/s or counts/minute Supplement 5 Use measurements of background radiation to determine a corrected count rate

5.2.2 The three types of nuclear emission

CORE OBJECTIVES:

  • Describe the emission of radiation from a nucleus as spontaneous and random in direction
  •  Identify alpha (?), beta (?) and gamma (?) emissions from the nucleus by recalling:
  • (a) their nature
  • (b) their relative ionising effects
  • (c) their relative penetrating abilities (?+ are not included, ?-particles will be taken to refer to ?– )

EXTENDED/SUPPLEMENT OBJECTIVES:

  •  Describe the deflection of ?-particles, ?-particles and ?-radiation in electric fields and magnetic fields
  •  Explain their relative ionising effects with reference to: (a) kinetic energy (b) electric charge5.2.3 Radioactive decay

CORE OBJECTIVES:

  • Know that radioactive decay is a change in an unstable nucleus that can result in the emission of ?-particles or ?-particles and/or ?-radiation and know that these changes are spontaneous and random
  •  State that during ?-decay or ?-decay, the nucleus changes to that of a different element

EXTENDED/SUPPLEMENT OBJECTIVES:

  • Know that isotopes of an element may be radioactive due to an excess of neutrons in the nucleus and/or the nucleus being too heavy
  •  Describe the effect of ?-decay, ?-decay and ?-emissions on the nucleus, including an increase in stability and a reduction in the number of excess neutrons; the following change in the nucleus occurs during ?-emission neutron ? proton + electron
  •  Use decay equations, using nuclide notation, to show the emission of ?-particles, ?-particles and ?-radiation

5.2.4 Half-life

CORE OBJECTIVES:

  • Define the half-life of a particular isotope as the time taken for half the nuclei of that isotope in any sample to decay; recall and use this definition in simple calculations, which might involve information in tables or decay curves (calculations will not include background radiation)

EXTENDED/SUPPLEMENT OBJECTIVES:

  • Calculate half-life from data or decay curves from which background radiation has not been subtracted
  •  Explain how the type of radiation emitted and the half-life of an isotope determine which isotope is used for applications including:
  • (a) household fire
  • (smoke) alarms
  • (b) irradiating food to kill bacteria
  • (c) sterilisation of equipment using gamma rays
  • (d) measuring and controlling thicknesses of materials with the choice of radiations used linked to penetration and absorption
  • (e) diagnosis and treatment of cancer using gamma rays

.5.2.5 Safety precautions

CORE OBJECTIVES:

  • State the effects of ionising nuclear radiations on living things, including cell death, mutations and cancer
  •  Describe how radioactive materials are moved, used and stored in a safe way

EXTENDED/SUPPLEMENT OBJECTIVES:

  • Explain safety precautions for all ionising radiation in terms of reducing exposure time, increasing distance between source and living tissue and using shielding to absorb radiation

Revision Notes

Next Previous