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OCR Physics B Unit 5 > 5.4 Ionising Radiation and Risk > Flashcards

5.4 Ionising Radiation and Risk Flashcards

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1
Q

What is the symbol and constituent of alpha radiation?

A

α. A helium nucleus (2 protons and 2 neutrons).

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2
Q

What is the symbol and constituent of beta(-minus) radiation?

A

β or β-. An electron.

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3
Q

What is the symbol and constituent of beta-plus radiation?

A

β+. A positron.

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4
Q

What is the symbol and constituent of gamma radiation?

A

𝛾. An EM wave with a very high frequency.

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5
Q

What is the relative charge of alpha radiation?

A

+2

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6
Q

What is the relative charge of beta radiation?

A

-1

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7
Q

What is the relative charge of beta-plus radiation?

A

+1

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8
Q

What is the relative charge of gamma radiation?

A

0

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9
Q

What is the relative mass of alpha radiation?

A

4u

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10
Q

What is the relative mass of beta radiation?

A

Negligible

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11
Q

What is the relative mass of beta-plus radiation?

A

Negligible

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12
Q

What is the relative mass of gamma radiation?

A

0

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13
Q

Describe the properties of alpha radiation.

A

It is strongly ionising but slow moving and can be absorbed by paper or a few centimetres of air. It is affected by a magnetic field.

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14
Q

Describe the properties of beta radiation.

A

It is weakly ionising and fast moving. It can be absorbed by around 3mm of aluminium. It is affected by a magnetic field.

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15
Q

Describe the properties of beta-plus radiation.

A

It is annihilated by electrons so has a range of virtually zero.

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16
Q

Describe the properties of gamma radiation.

A

It is very weakly ionising but travels at the speed of light. It is absorbed by many centimetres of lead or several metres of concrete.

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17
Q

What is the relationship between intensity of a gamma source and the distance it travels through an absorbing material?

A

Exponential.

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18
Q

What is the ‘absorbed dose” of ionising radiation?

A

The energy absorbed per kilogram of tissue.

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19
Q

What are the units of absorbed dose?

A

Grays, Gy.

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20
Q

Give the equation for absorbed dose.

A

Absorbed dose = energy / mass

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21
Q

What factors affect tissue damage done by ionising radiation?

A

The type of ionising radiation and the type of body tissue.

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22
Q

What is the use of effective dose of radiation?

A

It allows you to compare the amount of damage done to body tissues that have been exposed to different types of radiation.

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23
Q

What is the equation used to find effective dose?

A

Effective dose = absorbed dose x radiation quality factor

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24
Q

What are the units of effective dose?

A

Sieverts, Sv.

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25
Q

Give typical values of the quality factor of alpha, beta and gamma radiation respectively.

A

20, 1, 1.

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26
Q

Explain why alpha radiation causes so much damage to body tissue.

A

Alpha particles are very positive, allowing them to easily pull electrons off atoms. When an alpha particle ionises an atom it transfers some energy to it. One alpha particle quickly ionises around 10,000 atoms, transferring lots of energy and doing a lot of tissue damage.

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27
Q

Explain why beta radiation causes less damage to body tissue than alpha radiation.

A

Beta-minus particles have lower mass and charge than alpha particles but a higher speed. Each beta particle ionises around 100 atoms, far less than alpha particles, there it does less tissue damage.

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28
Q

Give the equation for risk.

A

Risk = probability x consequence

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29
Q

Give some uses of radioactive materials.

A

Power generation, medical diagnosis and treatment and sterilisation of food.

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30
Q

Give some dangers of radioactive materials.

A

They can cause cancerous tumours, sterility, skin burns, radiation sickness, hair loss death.

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31
Q

What does the nucleon number (mass number) of an isotope represent?

A

The total number of nucleons (protons and neutrons) that it contains.

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32
Q

In standard notation, where is the nucleon number displayed?

A

To the top left of the element symbol.

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33
Q

What is the proton (atomic) number of an isotope?

A

The number of protons that the isotope contains.

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34
Q

Where is the proton number displayed in standard notation

A

Bottom left of the symbol, directly below nucleon number.

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35
Q

Give four reasons as to why a nucleus may be unstable.

A

It may have too many or too few neutrons. It may have too many nucleons altogether (too heavy) or it may have too much energy.

36
Q

Where are beta-minus emitters on an N vs Z graph in relation to the line of stability?

A

Above it.

37
Q

What does an N vs Z graph represent?

A

N represents the number of neutrons in an isotope whilst Z represents the number of protons.

38
Q

Where are beta-plus emitters on an N vs Z graph in relation to the line of stability?

A

Below it?

39
Q

Where is the line of stability on an N vs Z graph in relation to the line N = Z?

A

They meet at the origin but the line of stability curves off above N = Z as Z increases.

40
Q

In which isotopes does alpha emission occur?

A

Isotopes with more than 82 protons.

41
Q

What happens to the proton and nucleon number of an isotope when an alpha particle is emitted?

A

The protons number decreases by two whilst the nucleon number decreases by four.

42
Q

In which nuclei does beta-minus emission happen?

A

Neutron rich nuclei. They have many more neutrons than protons.

43
Q

What happens to the proton and nucleon number of an isotope when an beta-minus particle is emitted?

A

The proton number increases by one whilst the nucleon number is unchanged.

44
Q

What type of radiation is emitted from nuclei with too much energy?

A

Gamma radiation.

45
Q

A nucleus with excess energy is said to be what?

A

Excited.

46
Q

How man excited nuclei lose energy?

A

By emitting a gamma ray.

47
Q

When does gamma emission often happen?

A

After an alpha or beta decay.

48
Q

Name four things that are always conserved in a nuclear reaction.

A

Energy, momentum, proton number or charge and nucleon number.

49
Q

Why doesn’t mass have to be conserved?

A

Because energy and mass are equivalent and energy is always conserved.

50
Q

What is the name of the difference in mass between individual protons and neutrons and an alpha particle?

A

The mass defect.

51
Q

What is the mass defect?

A

When nucleons bond together they released energy and lose mass. This energy lost is equivalent to the mass defect.

52
Q

What is binding energy?

A

The energy required to separate all of the nucleons in a nucleus. It is equivalent to the mass defect.

53
Q

Which nucleon number has the highest binding energy per nucleon?

A

50, Fe.

54
Q

Why is the binding energy negative?

A

Because the mass defect is negative.

55
Q

The more negative the binding energy per nucleon is…

A

The more energy is needed to remove nucleons from the nucleus.

56
Q

Fusion occurs to isotopes with which range of nucleon numbers?

A

1 to 49

57
Q

Fission occurs to isotopes with which range of nucleon numbers?

A

51+

58
Q

Why is a lot of energy realised by nuclear fusion?

A

The size of the binding energy per nucleon increases dramatically.

59
Q

How can you use a binding energy per nucleon graph to estimate the energy released from nuclear reactions?

A

Find the average change in binding energy per nucleon and multiply it by the number of nucleons involved in the reaction.

60
Q

What is nuclear fission?

A

When nuclei with at least 83 protons randomly split into two smaller nuclei.

61
Q

The larger the nucleus…

A

The more unstable it is likely to be and therefore fission is more likely to occur.

62
Q

How does spontaneous fission limit the number of possible elements?

A

The higher the proton number, the more unstable it is. Therefore elements with extremely high proton numbers don’t exist as they are too unstable.

63
Q

Name a common fuel used in fission reactors.

A

Uranium 235

64
Q

As well as two smaller nuclei, what else is produced in fission reactions?

A

Energy and neutrons.

65
Q

How can fission be induced?

A

Firing a neutron at an unstable nucleus.

66
Q

Why is fission a chain reaction?

A

The nucleons produced in one fission go on to induce other fissions.

67
Q

Neutrons will only cause a chain reaction if…

A

They are slowed down.

68
Q

What is the name for slowed down neutrons that are capable of inducing nuclear fission?

A

Thermal neutrons.

69
Q

How are neutrons slowed down to become thermal neutrons?

A

The fuel rods are place in a moderator such as water.

70
Q

Explain an important feature of a moderator used in fission reactors.

A

A good moderator absorbs more neutrons at higher temperatures and so decreases the risk of meltdown if a reactor overheats.

71
Q

What is critical mass?

A

The amount of fuel needed to maintain a steady, one to one, fission chain reaction.

72
Q

What happens to a chain reaction if the amount of fuel is sub-critical mass?

A

It will peter out.

73
Q

Do nuclear reactors use a critical mass?

A

No, they used a supercritical mass of fuel and use control rods to control the rate of fission.

74
Q

How do control rods control the chain reaction?

A

They absorb neutrons.

75
Q

What are control rods usually made of?

A

Boron.

76
Q

What happens when a nuclear reaction is shutdown in an emergency?

A

The boron control rods are released into the reactor, stopping the reaction as quickly as possible.

77
Q

How do nuclear reactor generate electricity?

A

The heat from the reactor is used in steam to drive electricity-generating turbines.

78
Q

Why are waste products of fission dangerous?

A

Because they contain lots of unstable nuclei and are radioactive.

79
Q

Give one use for nuclear waste.

A

Medical tracers.

80
Q

How is nuclear waste dealt with safety?

A

It is placed in a cooling pond until the temperature falls to a safe level, then is stored in sealed containers until activity has fallen sufficiently.

81
Q

What is nuclear fusion?

A

When two light nuclei cosine to made a larger nucleus.

82
Q

Nuclei can only fuse if…

A

They have sufficient energy to overcome the electrostatic repulsion between them and get close enough for the strong face to bind them.

83
Q

How much energy is needed for nuclei to fuse?

A

Around 1 MeV of kinetic energy.

84
Q

Where does fusion often happen?

A

In the core of stars because the temperature is so high.

85
Q

What is plasma?

A

Positively charged nuclei and free electrons in a mixture.

86
Q

How does one fusion reaction help another occur?

A

A lot of energy is related in one fusion, which could give other nuclei the kinetic they need to fuse.

87
Q

Why don’t we currently use nuclear fusion as a source of energy?

A

Electricity generated is less than the amount needed to get the reactor up to the required temperature.

OCR Physics B Unit 5 (4 decks)

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