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Physics Gcse > Topic 6 - Radioactivity > Flashcards

Topic 6 - Radioactivity Flashcards

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1
Q

What is an atom

A

A positively charged nucleus, consisting of protons and neutrons. Surrounded by negatively charged electrons, with the nuclear radius much smaller than that of the atom and with almost all of the mass in the nucleus

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2
Q

What is the radius of an atoms

A

1x10-10 metres

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3
Q

What proportion of the total radius of an atom is the radius of the nucleus?

A

1/10,000

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4
Q

Give two ways than an atoms electron arrangement can be changed?

A

Absorbing electromagnetic radiation

Emitting electromagnetic radiation

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5
Q

Explain how an atoms electron arrangement changed when it absorbs em radiation?

A

Electrons Move to higher energy levels

They move away from the nucleus

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6
Q

Explain how an atoms electrons arrangement changes when it emits EM radiation

A

Electrons move to a lower energy level

They move towards the nucleus

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7
Q

Ratio of electrons to protons

A

They are the same 1:1 therefore no overall charge in the Atom

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8
Q

What is an isotope

A

Atoms of an element that has same atomic number but different number of neutrons

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9
Q

How do atoms turn into positive ions

A

They lose one or more of their outer electrons

Electrons are negatively charged, so the resultant charge of the atom is positive

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10
Q

Relative mass and charge of protons, neutron, electron

A

1 - proton + 1
1 - neutron - 0
1/1850 - electron - (-1)

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11
Q

State four types of nuclear radiation

A

Alpha particles
Beta particles
Gamma rays
Neutrons

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12
Q

What is meant by background radiation

A

Radiation that is Always present

It is in very small amount and so not harmful

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13
Q

Give 4 sources of background radiation

A

Rocks
Cósmic rays from space
Nuclear weapon testing
Nuclear accidents

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14
Q

How do you measure and detect background radiation?

A

Photographic film

Geiger-Müller counter

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15
Q

How is photogenic film used to measure radiation?

A

A photographic film turns dark when it absorbs radiation. This is useful for people who work on radiation as the more radiation they are exposed to, the darker the film becomes. Therefore the workers know when they have been exposed to too much radiation

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16
Q

How is Geiger-Muller tubes used to measure radiation?

A

When the Geiger-Muller tube absorbs radiation it produces a pulse, which a machine uses to count the amount of radiation. The frequency of the pulse depends on how much radiation is present. A high frequency would mean the tube is absorbing a large amount of radiation.

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17
Q

What constitutes an alpha particle?

A

Two protons and two neutrons

It is the same as a helium nucleus

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18
Q

What is the range of an alpha particle through air?

A

A few centimetres (normally in the range of 2-10cm).

Stopped by paper

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19
Q

What will block beta radiation?

A

A thin sheet of aluminium

Several metres of air

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20
Q

What will block gamma radiation?

A

● Several centimetres of lead

● A few metres of concrete

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21
Q

Which type of radiation is most ionising?

A

Alpha radiation.

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22
Q

Which type of radiation is least ionising?

A

Gamma radiation

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23
Q

How does gamma emission affect mass/charge of an atom?

A

Both mass and charge remain unchanged.

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24
Q

Describe the plum-pudding model of the atom

A

A sphere of positive charge, with the negatively charged electrons distributed evenly throughout it.

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25
Q

Prior to the discovery of the electron what was believed about the atom?

A

The atom was believed to be indivisible.

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26
Q

Which experiment led to the plum-pudding model being discarded?

A

Rutherford’s alpha-Scattering experiment.

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27
Q

What is the name given to the currently accepted model of the atom?

A

The Bohr model.

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28
Q

Describe Rutherford’s experiment

A

Alpha particles (charge +2) were fired at a thin sheet of gold foil
● Most particles went straight through
● Some particles were deflected by small angles
(< 90o)
● A few particles were deflected by large angles
(> 90o)
hwtwtpws.:p//mbit.leyd/pumcat-teiod

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29
Q

What are the conclusions of Rutherford’s experiment?

A

● Most of an atom is empty space
● The nucleus has a positive charge
● Most of the mass is concentrated in the nucleus

30
Q

What happens in the process of beta plus decay?

A

A proton turns into a neutron and a positron (in order to conserve charge).

31
Q

What is the process called when a neutron changes into a proton and an electron?

A

Beta minus decay.

32
Q

When alpha decay occurs, what happens to the atomic number and the mass number of the atom?

A

The atomic number decreases by 2
● The mass number decreases by 4
● A new element is made since the atomic number has changed

33
Q

What effect does beta minus decay have on the mass number and atomic number of an atom?

A

The mass number stays the same as the total number of neutrons and protons hasn’t changed (one has just turned in the other).

The atomic number increases since there is one more proton.

34
Q

Define the activity of an unstable nucleus.

A

Activity is the rate at which a source of unstable nuclei decays.

35
Q

What is the unit of radioactive activity?

A

Becquerel (Bq)

36
Q

What is count-rate?

A

The number of radioactive decays per second for a radioactive source.

37
Q

Give an example of a detector that may be used to measure count-rate.

A

Geiger-Muller tube

38
Q

Describe the nature of radioactive decay.

A 
Random
● Which nuclei decays and when is
determined only by chance
● It is impossible to predict which nuclei
will decay and when
39
Q

Define the half-life of a radioactive isotope

A

● The time it takes for the number of unstable nuclei in a substance to halve
● The time it takes for the count rate from a sample to fall to half its initial level

40
Q

Give example uses of radioactivity.

A

Household fire alarms (smoke)
● Irradiating food
● Sterilisation of equipment
● Tracing and gauging thicknesses of materials ● Diagnosis and treatment of cance

41
Q

How do smoke alarms work?

A

A radioactive substance is in the alarm which emits alpha radiation

The emitted alpha particle ionises the air in the detector and causes a current to flow between the plates

When smoke interferes with the radiation, the air is no longer ionised and so no current can flow

● This reduction in current flow triggers the alarm

42
Q

State two uses of nuclear radiation in the field of medicine.

A

Examining of internal organs

  1. Radiotherapy in the treatment of cancer
43
Q

What is the role of beta radiation in tracers?

A

The tracer is inserted in your body, and targets a specific part of the body
● The radioactive substance in the tracer releases beta radiation which can be detected
by external machines

44
Q

How is beta radiation used to determine thickness?

A

A beta source is placed above the material and a detector is placed below it
● If there is an increase in radiation detected by the detector, too much radiation is passing through the material, and so it is too thin
● If there is a decrease in radiation is detected, then the material blocks too much radiation, and so it is too
thick

45
Q

Why is ionising radiation dangerous?

A

It can damage tissue and kill cells

● It can cause cell mutations

46
Q

What is a consequence of cell mutation?

A

Cancer.

47
Q

What precautions should people take when using ionising radiation?

A

● Avoid handling the source directly (use tongs)
● Wear radiation protective clothing
● Keep the radiation in lead containers to reduce
the amount of radiation that can escape
● Keep exposure time to a minimum

48
Q

Does a long half life or a short half life make a source more dangerous?

A

If it has a long half life then it would

remain highly radioactive for longer therefore making it more dangerous.

49
Q

What precautions are taken to reduce harm for doctors and patients using ionising radiation?

A

Only a small dose is given to the patient so they are not exposed to too much.
● The radiation used has a short half life so it won’t remain highly radioactive for long. This reduces the risk to the doctors using it as well as the patient.
● Doctors and patients (when applicable) wear protective clothing

50
Q

What is radioactive contamination?

A

The presence of unwanted radioactive nuclei on other materials.

51
Q

What is irradiation?

A

● The process of exposing a material to nuclear radiation

● The material does not become radioactive

52
Q

How is a radioactive tracer used in medicine?

A

The tracer is placed inside the body (it can be in a drink, eaten or injected)
● The tracer releases gamma radiation which is detected by a detector which moves around the body
● This can then be used to produce a picture of the patient’s body

53
Q

How does a PET scanner work?

A

● PET (positron emission tomography) uses a tracer, which is injected into the patient’s body
● The scanner detects the gamma rays which are released by the trace
● Multiple images are taken and this is used to form a 3D image of the patient’s body

54
Q

Isotopes are used in PET scanners. What is important about where they are produced and why?

A

They must be produced near the hospital because the isotopes used have a short half life so must be used soon after production.

55
Q

Describe the advantages of nuclear power for generating electricity.

A

● Nuclear fuels do not produce carbon dioxide
The fuel is readily available, so would reduce strain on the fossil fuel supplies
● Less nuclear fuel has to be used to produce the same
amount of energy as burning fossil fuel
● Does not contribute to global warming

56
Q

Explain some disadvantages of using nuclear power to generate electricity.

A

Unpopular - the public perceive nuclear power as very dangerous
● Security risks as the radioactive substances can be useful for
terrorists
● Expensive to commission and decommission the stations - which may
be bad for a country’s economy
● The radioactive waste can be difficult to dispose of and will remain
radioactive for many years - which can be dangerous to humans and
the environment
● Risk of nuclear accidents

57
Q

What is nuclear fission?

A

The splitting of large, unstable nuclei to form smaller more stable nuclei (+ the emission of spare neutrons).

58
Q

What usually needs to happen to induce fission?

A

● The unstable nuclei must absorb a neutron

● Spontaneous fission (where no neutron absorption occurs) is rare

59
Q

Alongside two smaller nuclei, what else is emitted in a fission reaction?

A

Two or three neutrons
● Gamma rays
● Energy

60
Q

Name a common fissile nuclei.

A

Uranium-235

61
Q

What are the three main components of the core a nuclear reactor?

A

1) Fuel rods
2. Control rods
3. Moderator

62
Q

What takes place during a chain reaction in a nuclear reactor?

A 
● An unstable nucleus absorbs a neutron
● The nucleus undergoes fission and
releases 2 or 3 further neutrons
● These induce more fission, which results
in a chain reaction
63
Q

What is the consequence of an uncontrolled chain reaction?

A

● The rate of fission eventually becomes too high and results in the production of too much energy
● This can lead to a nuclear explosion

64
Q

How is the chain reaction in a fission reactor kept under control?

A

● Control rods are positioned in between the fuel rods
● The rate of fission is controlled by moving these rods up and down
● The lower the rods are inserted, the slower the rate of fission

65
Q

What is the role of the moderator in a nuclear reactor?

A

To slow down the neutrons so they are travelling at speeds which allow them to be absorbed by fissile nuclei and cause fission.

66
Q

How is electricity produced in a nuclear power station?

A

● The reactions release thermal energy
● The thermal energy is used to boil water and
then produce steam.
● This steam is then used to turn a turbine which
starts the generator.

67
Q

What is nuclear fusion?

A

When two light nuclei join to produce a heavier nucleus and release energy

68
Q

Name two isotopes of hydrogen which are commonly used in nuclear fusion.

A

Deuterium and Tritium

69
Q

Which releases more energy, nuclear fission or nuclear fusion?

A

Nuclear fusion.

70
Q

Explain the difficulty of generating energy through nuclear fusion

A

Fusion requires very high temperatures which in itself requires large quantities of energy. Currently, the production of fusion results in a net loss of energy

71
Q

Give an example of where fusion occurs?

A

In the sun - stars use fusion as their energy source.

72
Q

Why does nuclear fusion require so much energy?

A

This is because both nuclei are positive therefore a lot of energy is required to overcome the electrostatic repulsion between the two nuclei.

Physics Gcse (21 decks)

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