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AQA GCSE PHYSICS > P7 - Radioactivity > Flashcards

P7 - Radioactivity Flashcards

1
Q

What discovery was made by Henri Becquerel in 1896?

A

Henri Becquerel was a French physicist

He discovered the image of a key on a photographic film he developed.
The film had been in a draw under a key.
Above that was a packet of uranium salts.

He concluded that the uranium salts must have emitted some form of radiation that passed through the paper but not the metal key.

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2
Q

What did Marie Curie concluded from her investigations?

A

The uranium salts emitted radiation all the time.
She used the word “radioactivity” to describe this property.

She and her husband Pierre did further research and discovered new radioactive elements such as Radium and Polonium

Polonium - named after Poland as Marie Curie was Polish

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3
Q

What apparatus can be used to detect radioactivity?

A

A Geiger Counter

This is a Geiger-Müller tube connected to an electronic counter.

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4
Q

How does a geiger counter work?

A

It clicks each time a radioactive particle enters the Geiger tube

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5
Q

What three forms of radiation are there?

A

Alpha
Beta
Gamma

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6
Q

Order the forms of radiation from the highest penetrating power to the lowest

A

Gamma
Beta
Alpha

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7
Q

Order the forms of radiation from the most to least ionising

A

Alpha
Beta
Gamma

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8
Q

What material can stop alpha particles?

A

Paper

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9
Q

What material can stop beta particles?

A

Aluminium

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10
Q

What material can stop gamma rays?

A

1 metre thick concrete or thick lead

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11
Q

How far will gamma rays travel when not stopped?

A

Indefinitely (forever)

This is because they spread out in the air and are not absorbed

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12
Q

How far can alpha particles travel when not stopped?

A

5cm

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13
Q

How far can beta particles travel when not stopped?

A

1 metre

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14
Q

Who discovered Alpha and Beta radiation? What did he discover about the two?

A

Ernest Rutherford

He discovered:
Alpha radiation was stopped by paper
Beta radiation could pass through paper

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15
Q

Which element does an Alpha particle resemble

A

Helium

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16
Q

What did Rutherford discover about alpha particles?

A

They were stopped by paper
Made up of positively charged particles
They could be used to probe the atom

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17
Q

Describe and name the experiment conducted by Hans Geiger and Ernest Rutherford?

A

Gold Foil Experiment

Narrow beam of Alpha (A) particles directed at a thin metal foil
Some A particles rebounded

Rutherford proved that this happens because every atom has a positively charged at its centre, which contains most of the atom’s mass.

Rutherford went on to propose the nucleus contains protons and neutrons.

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18
Q

Describe the nucleus of a radioactive substance’s atoms

A

Unstable

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19
Q

How does an unstable nucleus become stable?

A

It emits alpha, beta, or gamma radiation

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20
Q

Why was the apparatus in the Gold Foil experiment in a vacuum?

A

So the air molecules do not absorb the alpha particles

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21
Q

Describe the Alpha Scattering experiment

A

Conducted by Hans Geiger and Ernest Marsden
Investigated how a thin metal foil scatters a beam of alpha particles

The apparatus was in a vacuum chamber to prevent air molecules from absorbing the alpha particles
The detector consisted of a microscope focused on a small glass plate.

Each time an alpha particle hit the plate, a spot of light was observed

The detector was moved to different positions
At each position, the number of spots of light observed in a certain time was counted

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22
Q

What were the results of the Alpha Scattering experiment?

A

Most alpha particles passed straight through the metal foil
The number of alpha particles deflected per minute decreased as the angle of deflection increased
About 1 in 10,000 alpha particles were deflected by over 90°

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23
Q

From the Alpha Scattering experiment, what did Rutherford concluded?

A

The nucleus of the atom is much smaller than the atom as most Alpha particles pass through without deflection

The nucleus holds most of the atom’s mass

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24
Q

Why was Rutherford’s nuclear model of the atom quickly adopted?

A

It agreed exactly with the measurements Geiger and Marsden made with the experiments

It explained radioactivity in terms of changes that happen to an unstable nucleus when it emits radiation

It predicted the existence of the neutron which was later discovered

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25
Q

Before the nucleus’ discovery in 1914, what did scientists know about atoms?

A

The contained tiny negatively charged particles (electrons)

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26
Q

What did the plum pudding model depict?

A

Positively charged matter spread evenly, with electrons buried inside

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27
Q

What theory did Niels Bohr propose?

A

Electrons orbit the nucleus at specific distances and specific energy levels

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28
Q

What did Bohr’s model of the atom show about electrons?

A

They can leap to another orbit by:

Absorbing electromagnetic radiation - moves away from the nucleus

Emitting electromagnetic radiation - moves closer to the nucleus

His calculations based on his atomic model agreed with experimental observations of the light emitted by atoms.

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29
Q

What did further Alpha scattering experiments show?

A

Hydrogen nuclei have the least amount of charge

Charge of any nucleus is shared equally between a whole number of smaller particles, each with an equal positive charge

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30
Q

How was the neutron discovered?

A

The name ‘proton’ was given to the Hydrogen nucleus because scientists reckoned that every other nucleus contained H nuclei

However they also knew that the mass of every nucleus was bigger than the total mass of its protons
This applied to every element BUT Hydrogen

They theorised that there must be an uncharged type of particle - the neutron

Direct experimental evidence for the neutron’s existence was found by James Chadwick about 20 years after the discovery of the nucleus

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31
Q

What is an alpha particle made up of?

A

Two protons
Two neutrons
Relative mass of 4
Relative charge of 2+

Therefore identical to a Helium nucleus

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32
Q

What happens to an unstable nucleus when an Alpha particle is emitted?

A

Atomic number decreases by 2
Mass number goes down by 4
Mass and charge of nucleus are both reduced

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33
Q

What is a beta particle? State its mass and charge, also.

A

An electron
Mass of effectively 0
Relative charge of -1

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34
Q

How are beta particles emitted?

A

Nucleus has too many neutrons
A neutron converts into a proton
Electron released at the same time

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35
Q

What happens to an unstable nucleus when it emits a Beta particle?

A

Atomic number of nucleus goes up
Mass number is unchanged
Charge of nucleus is increased
Mass of nucleus is unchanged

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36
Q

What is a gamma ray?

A

An electromagnetic wave

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37
Q

What is the mass and charge of Gamma radiation?

A

No mass

No charge

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38
Q

How are neutrons emitted?

A

Particles collide with unstable nucleus
Unstable nucleus becomes more unstable
Neutron is emitted

Neutrons are uncharged and so they can pass through substances more easily than alpha and beta particles

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39
Q

Describe the experiment to determine the penetration power of radiation?

A

Apparatus:
Source sealed in a container
Absorber
Geiger counter

1) Measure the count rate without the radioactive source present. This is the BACKGROUND count rate (BCR)
2) Measure the count rate with the radioactive source present (RCR)
3) Subtract the BCR from the RCR (BCR - RCR) to give you the count rate of the radioactive substance alone.

TO TEST PENETRATING POWER:

4) Place different absorber materials between the geiger counter’s tube and the radioactive source
5) Increase the thickness of the absorber material until the count rate ( RCR - BCR) equals 0. This is the minimum thickness of the material needed to stop the radiation.

TO TEST RANGE:

4) Move the Geiger tube further away from the source.
5) When the tube is out of the radiation’s range, the count rate will be 0

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40
Q

What is ionisation and how can radiation cause it?

A

Ionisation - an atom gaining a charge

Radiation from a radioactive substance can knock electrons out of the atoms. The atoms become charged because they lose electrons (ionisation).

41
Q

What is irradiation?

A

When an object is exposed to ionising radiation but does not become radioactive

42
Q

What is radioactive contamination?

A

The unwanted presence of materials containing radioactive atoms on other materials.

43
Q

Where does the hazard of radioactive contamination come from?

A

The decay of the nuclei of the contaminating atoms. Type of radiation affects level of hazard

44
Q

What two electromagnetic waves can cause ionisation?

A

X-Rays

Gamma rays

45
Q

How do X-rays cause ionisation?

A

Fast moving protons

Fast moving neutrons

46
Q

What can happen to a living cell if it becomes ionised?

A

It can be damaged or killed

Damage to the genes in a cell can be passed on if the cell generates more cells.

47
Q

How can workers reduce their exposure to radiation?

A

Keep as far away as possible from the source of the radiation
Example: use special handling tools with long handles

Spend as little time as possible in at-risk areas

Shield themselves by staying behind thick concrete barriers or by using thick lead plates

48
Q

What is peer reviewing?

A

Publishing of findings by scientists so they can be checked by other scientists
It helps to ensure no false data.

49
Q

How do smoke alarms work?

A

Radioactive substance in smoke alarm releases Alpha particles

When no smoke is present:
The alpha particles ionise the air particles
Air particles now has a charge
Air particles fill the gap in the smoke alarm
This completes the circuit
A current is then able to pass through
The smoke alarm does NOT sound

When smoke is present:
Smoke ABSORBS alpha particles
Smoke is NOT ionised
Smoke tries to fill the gaps in the smoke alarm
Does not succeed
Circuit is incomplete
Current is unable to flow through
Smoke alarm goes off
50
Q

Why can’t gamma or beta radiation be used in smoke alarms?

A

They do not ionise the air enough to conduct electricity

51
Q

How does Automatic Thickness Monitoring in metal foil production work?

A

Uses a radioactive source which emits Beta particles
Amount of Beta radiation passing through the foil depends on its thickness

Detector measures amount of radiation passing through

Foil too thick:
Detector reading drops
Detector sends a signal to increase the pressure of the rollers on the metal sheet
Makes foil thinner

52
Q

Why arent gamma or alpha radiation used for Automatic Thickness Monitoring?

A

Gamma - Passes through foil unaffected

Alpha - Stopped completely by the foil

53
Q

What is the activity of a radioactive source?

A

Number of unstable atoms in the source that DECAY PER SECOND

Measured in Bq (Becquerel)
1 decay per second

54
Q

As the nucleus of each unstable atom decays, what happens?

A

The number of parent atoms decrease

Activity of sample decreases

55
Q

What can be used to monitor the activity of a radioactive sample?

A

A Geiger Counter

56
Q

The average time taken for the count rate / number of nuclei of the isotope to fall by half is always the _____?
This is called the ____ ____.

A

Same

Half
Life

57
Q

Radioactive decay is a ______ process.

What does this mean?

A

Random

No one can predict exactly when an individual atom will suddenly decay.
However you can predict how many atoms will decay in a given time

58
Q

How do radioactive transfers work?

A

They trace the flow of a substance through an organ
The tracer contains a radioactive isotope that emits gamma radiation
Gamma radiation is used as it can be detected outside the system

Before the test, the patient drinks water containing a tiny amount of the radioactive substance

The tracer can detect the gamma radiation emitted by the substance as it travels through the body

59
Q

Describe how radioactive iodine and a radioactive tracer can be used to find out if a patient’s kidney is blocked

A

Water containing a small amount of iodine is drunk by patient
Detectors are placed on each kidney
Each detector is connected to a chart recorder

Iodine flows in and out of a normal kidney; detector reading goes up then down

Iodine does not flow through a blocked kidney; detector reading goes up and stays up

Iodine is used because:

Half life of eight days - long enough for the test to be run, short enough to avoid major damage

Emits gamma radiation

Decays into a stable product

60
Q

How do gamma cameras work?

A

Patient injected with a solution that contains a gamma emitting radioactive isotope
Solution is absorbed by the organ
Nearby gamma camera detects gamma radiation

Gamma rays pass through the holes in the thick lead grid in front od the detector

Detector detects gamma rays from nuclei directly in front of it

Detector signals are used to build up an image of the location of the radioactive isotope

Radioactive isotope must be a gamma emitter with a half life long enough to give a useful image but short enough so that its nuclei has mostly decayed after the image has been taken

61
Q

How can gamma radiation be used to destroy tumours?

A

Uses a narrow beam of gamma radiation
Radiation emitted by radioactive isotope of cobalt
Half life of five years
Gamma radiation is used because it can penetrate the furthers into the body

62
Q

How can radioactive implants be used to destroy cancer cells?

A

Beta or gamma emitting isotopes are used in the form of small seeds or tiny rods

Permanent implants use isotopes with half lives long enough to irradiate the tumour over a given time, but short enough so most of its nuclei decays soon afterwards

63
Q

What is nuclear fission?

A

The splitting of a nucleus into two smaller nuclei of roughly equal size to release several neutrons.
This is induced fission.

Very rarely happens without a neutron being absorbed.
This is called spontaneous fission - the nucleus splits and several neutrons are released.

64
Q

What is released by nuclear fission?

A

Two or three neutrons at high speeds
Energy in the form of gamma radiation
Kinetic energy is stored in the fission neutrons and fragment nuclei

65
Q

What is a chain reaction of fission events?

A

A fission event releases several neutrons
This can cause other fissionable nuclei to split
The cycle repeats
This is a chain reaction

66
Q

What do most nuclear reactors use as the fuel?

A

Enriched uranium

This is made up of 2-3% of the fissionable uranium isotope and a lot of the non-fissionable uranium isotope

67
Q

How are uranium fuel rods spaced out in a reactor core?

A

They are spaced out evenly

68
Q

What does a reactor core contain?

A

Fuel rods
Control rods
Water at a high pressure

69
Q

What do the water molecules do to the fission neutrons in a reactor?

A

Collisions with the atoms in the water molecules slow them down

70
Q

Why do the fission neutrons need to be slowed down?

A

Fast neutrons dont cause further fission of Uranium-235

71
Q

The water is called a what?

A

Moderator

72
Q

What do control rods in a nuclear reactor do?

A

They absorb surplus neutrons.

This keeps the chain reaction under control

73
Q

Why are the depths of the control rids adjusted?

A

To maintain a steady chain reaction

74
Q

What cools down the fuel rods when they become very hot?

A

The water

75
Q

What happens to the water molecules’ kinetic energy stores?

A

They increases as energy is transferred from the neutrons and fuel rods.

76
Q

Through what is the water pumped?

A

The core

77
Q

From the core, where does the water go?

A

The sealed pipes to and from a heat exchanger outside the core.

78
Q

What happens at the heat exchanger?

A

The water transfers energy from the core to the heat exchanger.

79
Q

What is the reactor core made of?

A

Very thick steel

80
Q

Why is the reactor core made of very thick steel?

A

To withstand high pressures and temperatures

81
Q

In what is the reactor core?

A

A vessel

82
Q

What is the vessel of the reactor enclosed by? What do they do?

A

Thick concrete walls.

They absorb ionising radiation that escapes through the walls of the steel vessel

83
Q

How do stars release energy?

A

Nuclear fusion

84
Q

What is nuclear fusion?

A

The fusion of two like nuclei to form a larger nuclei

i.e
Hydrogen to Helium

85
Q

Some of the mass of the small nuclei is converted into what?

A

Energy

86
Q

What is some of the energy released by nuclear fusion transferred as?

A

Nuclear radiation

87
Q

What is the heaviest element that can be created via nuclear fusion?

A

Iron

88
Q

What is the Sun’s core made of?

A

Plasma of bare nuclei; it has no electrons

89
Q

What are some technical difficulties of making a fusion reactor?

A

Plasma of light nuclei has to be heated to very high temperatures and very high pressures

90
Q

Why are high pressures and temperatures needed for fusion?

A

The nuclei needs enough kinetic energy to overcome the repulsive force of their positive charges

91
Q

What would happen in a fusion reactor?

A

Plasma is heated by passing a very large electric current through it

Plasma is contained by a magnetic field so that it doesnt touch the reactor walls

If plasma touched the walls, it would go cold and the fusion would stop

92
Q

What is needed for a fusion reactor to be successful?

A

Has to release more energy than what is used to heat the plasma

93
Q

What is the unit of measurement for radistion doses?

A

Sieverts (Sv)

Milisieverts (mSv)

94
Q

List some causes of background radiation

A 
Cosmic rays
Ground & buildings
Food & drink
Natural radioactivity of the air
Medical applications
Nuclear weapon tests
Air travel
Nuclear power
95
Q

Where are used fuel rods stored and for how long?

A

Big tanks of water for up to a year

96
Q

What are used to open the fuel rods?

A

Remote control machines

97
Q

What happens to the unused uranium and plutonium?

A

They are removed chemically from the used fuel and stored in sealed containers to be used again

98
Q

Why does the remaining waste have to be stored in secures conditions?

A

To prevent radioactive contamination of the environment.

The isotopes have very long half lives.

AQA GCSE PHYSICS (2 decks)

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