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Physics > Topic 6 - radioactivity > Flashcards

Topic 6 - radioactivity Flashcards

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1
Q

What is the radius of an atom?

A

1x10^-10 metres

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2
Q

What are the stree subatomic constituents of an atom?

A

Proton
Neutron
Electron

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3
Q

Where is most of the mass of an atom concentrated?

A

In the nucleus

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4
Q

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

A

1/10,000

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5
Q

Where are protons found?

A

In the nucleus

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6
Q

Where are electrons found?

A

In discrete energy levels (shells) around the nucleus

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7
Q

Where are neutrons found?

A

In the nucleus

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8
Q

What charge does the nucleus of an atom have? Why?

A

A positive charge
It contains protons and neutrons
Protons are positive
Neutrons have no charge

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9
Q

Give two ways that an atom’s electron arrangement can be changed

A

Absorbing electromagnetic radiation

Emitting electromagnetic radiation

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10
Q

Explain how an atom’s electron arrangement changes when it absorbs EM radiation

A

The electrons move to higher energy levels (away from the nucleus)

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11
Q

Explain how an atom’s electron arrangement changes when it emits EM radiation

A

Electrons move to a lower energy level (towards the nucleus)

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12
Q

How does the ratio of electrons to protons in an atom result in the atom having no overall charge?

A

The number of protons is equal to the number of electrons

Protons are positive and electrons are negative so it evens out

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13
Q

What do all forms of the same element have in common?

A

The number of protons

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14
Q

What is the name given to the number of protons in an atom?

A

Atomic number

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15
Q

What is an atom’s mass number?

A

The total number of protons and neutrons in an atom

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16
Q

What is an isotope of an atom?

A

An atom of an element that has a different number of neutrons, but the same number of protons

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17
Q

What property differs between isotopes of an atom?

A

The mass of the atom

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18
Q

How do atoms turn into positive ions?

A

The 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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19
Q

What are the relative masses of a proton, neutron and electron?

A 
Proton = 1
Neutron = 1
Electron = 1/1850
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20
Q

What is the relative charge of a proton?

A

+1

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21
Q

What is the relative charge of an electron?

A

-1

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22
Q

State four types of nuclear radiation

A

Alpha particles
Beta particles
Gamma rays
Neutrons

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23
Q

What is background radiation?

A

Radiation that is always present

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24
Q

Give four sources of background radiation

A

Rocks
Cosmic rays
Nuclear accidents
Nuclear weapon testing

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25
Q

How do you measure and detect background radiation?

A

Photographic film

Geiger-Müller counter

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26
Q

How is photographic film used to measure radiation?

A

It turns dark when it absorbs radiation

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27
Q

How are Geiger muller tubes used to measure radiation?

A

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

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28
Q

What constitutes an alpha particle?

A

Two protons and two neutrons

Same as a helium nucleus

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29
Q

What is the range of an alpha particle through air?

A

A few centimetres

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30
Q

What will block beta radiation?

A

A thin sheet of aluminium

Several metres of air

31
Q

What will block gamma radiation?

A

Several centimetres of lead

A few metres of concrete

32
Q

Which type of radiation is most ionising?

A

Alpha radiation

33
Q

Which type of radiation is least ion ionising?

A

Gamma radiation

34
Q

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

A

Both mass and charge remain unchanged

35
Q

Describe the plum-pudding model of the atom

A

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

36
Q

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

A

That is was indivisible

37
Q

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

A

Rutherford’s alpha scattering experiment

38
Q

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

A

The Bohr model

39
Q

Describe Rutherford’s experiment

A

Alpha particles were fired at a thin sheet of gold foil
Most particles went straight through
Some particles were deflected by small angles
A few particles were deflected by large angles

40
Q

What are the conclusions of rutherfors’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

41
Q

What happens in the process of beta plus decay?

A

A proton turns into a neutron and a positron

42
Q

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

A

Beta minus decay

43
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 4pa new element is made since the atomic number has changed

44
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
The atomic number increases since there is one more proton

45
Q

Define the activity of an unstable nucleus

A

Activity is the rate at chich a source of unstable nuclei decays

46
Q

What is the unit of radioactive activity?

A

Becquerel (Bq)

47
Q

What is count rate?

A

The number of radioactive decays per second for a radioactive source

48
Q

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

A

Geiger muller tube

49
Q

Give example uses of radioactivity

A 
Household fire alarms
Irradiating food
Sterilisation of equipment
Tracing and gauging thicknesses of materials
Diagnosis and treatment of cancer
50
Q

How do smoke alarms work?

A

A radioactive substance is in the alarm which emits alpha radiation
The emitted alpha particle ionised 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 so no current can flow.
This reduction in current flow triggers the alarm

51
Q

State two uses of nuclear radiation in the field of medicine

A

Examining of internal organs

Radiotherapy in the treatment of cancer

52
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

53
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 a decrease in radiation is detected then the material blocks too much radiation so it too thick

54
Q

Why is ionising radiation dangerous?

A

It can cause cell mutations

It can damage tissue and kill cells

55
Q

What is a consequence of cell mutation?

A

Cancer

56
Q

What precautions should people tale when using ionising radiation?

A

Avoid handling the source directly
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

57
Q

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

A

Only a small does is given
It has a short half life
They wear protective clothing

58
Q

What is radioactive contamination?

A

The presence of unwanted radioactive nuclei on other materials

59
Q

What is irradiation?

A

The process of exposing a material to nuclear radiation

The material does not become radioactive

60
Q

How is a radioactive tracer used in medicine?

A

It placed inside the body
It releases gamma radiation which is detected by a detector which moves around the body
Can then be used to produce a picture of the patient’s body

61
Q

How does a PET scanner work?

A

It uses a tracer
The scanner selects the gamma rays which are released by the tracer
Multiple images are taken and this Is used to form a 3C image of the patient’s body

62
Q

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

A

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

63
Q

What are the advantages of nuclear power for generating electricity?

A

Doesn’t produce carbon dioxide
Fuel is readily available
Less nuclear fuel used to produce the same amount of energy
Does not contribute to global warming

64
Q

What are the disadvantages of using nuclear power to generate electricity?

A

Unpopular
Security risks
Expensive to commission and decommission the stations
Radioactive waste can be hard to dispose of
Risk of nuclear accidents

65
Q

Hat is nuclear fission?

A

The splitting of large, unstable nuclei to form smaller, more stable nuclei

66
Q

What usually needs to happen to induce fission?

A

The unstable nuclei must absorb a neutron

67
Q

What is emitted in a fission reaction?

A

Gamma rays
Energy
2 or three neutrons
2 smaller nuclei

68
Q

Name a common fissile nuclei

A

Uranium - 235

69
Q

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

A

Fuel rods
Control rods
Moderator

70
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

71
Q

What is the consequence of an uncontrolled chain reaction?

A

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

72
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

73
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 simile nuclei and cause fission

74
Q

How is electricity produced in a nuclear power station?

A

The reactions release thermal energy which is used to boil water and produce steam which turns a turbine, starting the generator

Physics (12 decks)

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