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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
Before the nucleus' discovery in 1914, what did scientists know about atoms?
The contained tiny negatively charged particles (electrons)
26
What did the plum pudding model depict?
Positively charged matter spread evenly, with electrons buried inside
27
What theory did Niels Bohr propose?
Electrons orbit the nucleus at specific distances and specific energy levels
28
What did Bohr's model of the atom show about electrons?
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.
29
What did further Alpha scattering experiments show?
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
30
How was the neutron discovered?
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
31
What is an alpha particle made up of?
Two protons Two neutrons Relative mass of 4 Relative charge of 2+ Therefore identical to a Helium nucleus
32
What happens to an unstable nucleus when an Alpha particle is emitted?
Atomic number decreases by 2 Mass number goes down by 4 Mass and charge of nucleus are both reduced
33
What is a beta particle? State its mass and charge, also.
An electron Mass of effectively 0 Relative charge of -1
34
How are beta particles emitted?
Nucleus has too many neutrons A neutron converts into a proton Electron released at the same time
35
What happens to an unstable nucleus when it emits a Beta particle?
Atomic number of nucleus goes up Mass number is unchanged Charge of nucleus is increased Mass of nucleus is unchanged
36
What is a gamma ray?
An electromagnetic wave
37
What is the mass and charge of Gamma radiation?
No mass | No charge
38
How are neutrons emitted?
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
39
Describe the experiment to determine the penetration power of radiation?
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
40
What is ionisation and how can radiation cause it?
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
What is irradiation?
When an object is exposed to ionising radiation but does not become radioactive
42
What is radioactive contamination?
The unwanted presence of materials containing radioactive atoms on other materials.
43
Where does the hazard of radioactive contamination come from?
The decay of the nuclei of the contaminating atoms. Type of radiation affects level of hazard
44
What two electromagnetic waves can cause ionisation?
X-Rays | Gamma rays
45
How do X-rays cause ionisation?
Fast moving protons | Fast moving neutrons
46
What can happen to a living cell if it becomes ionised?
It can be damaged or killed Damage to the genes in a cell can be passed on if the cell generates more cells.
47
How can workers reduce their exposure to radiation?
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
What is peer reviewing?
Publishing of findings by scientists so they can be checked by other scientists It helps to ensure no false data.
49
How do smoke alarms work?
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
Why can't gamma or beta radiation be used in smoke alarms?
They do not ionise the air enough to conduct electricity
51
How does Automatic Thickness Monitoring in metal foil production work?
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
Why arent gamma or alpha radiation used for Automatic Thickness Monitoring?
Gamma - Passes through foil unaffected Alpha - Stopped completely by the foil
53
What is the activity of a radioactive source?
Number of unstable atoms in the source that DECAY PER SECOND Measured in Bq (Becquerel) 1 decay per second
54
As the nucleus of each unstable atom decays, what happens?
The number of parent atoms decrease | Activity of sample decreases
55
What can be used to monitor the activity of a radioactive sample?
A Geiger Counter
56
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 ____ ____.
Same Half Life
57
Radioactive decay is a ______ process. | What does this mean?
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
How do radioactive transfers work?
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
Describe how radioactive iodine and a radioactive tracer can be used to find out if a patient's kidney is blocked
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
How do gamma cameras work?
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
How can gamma radiation be used to destroy tumours?
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
How can radioactive implants be used to destroy cancer cells?
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
What is nuclear fission?
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
What is released by nuclear fission?
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
What is a chain reaction of fission events?
A fission event releases several neutrons This can cause other fissionable nuclei to split The cycle repeats This is a chain reaction
66
What do most nuclear reactors use as the fuel?
Enriched uranium This is made up of 2-3% of the fissionable uranium isotope and a lot of the non-fissionable uranium isotope
67
How are uranium fuel rods spaced out in a reactor core?
They are spaced out evenly
68
What does a reactor core contain?
Fuel rods Control rods Water at a high pressure
69
What do the water molecules do to the fission neutrons in a reactor?
Collisions with the atoms in the water molecules slow them down
70
Why do the fission neutrons need to be slowed down?
Fast neutrons dont cause further fission of Uranium-235
71
The water is called a what?
Moderator
72
What do control rods in a nuclear reactor do?
They absorb surplus neutrons. | This keeps the chain reaction under control
73
Why are the depths of the control rids adjusted?
To maintain a steady chain reaction
74
What cools down the fuel rods when they become very hot?
The water
75
What happens to the water molecules' kinetic energy stores?
They increases as energy is transferred from the neutrons and fuel rods.
76
Through what is the water pumped?
The core
77
From the core, where does the water go?
The sealed pipes to and from a heat exchanger outside the core.
78
What happens at the heat exchanger?
The water transfers energy from the core to the heat exchanger.
79
What is the reactor core made of?
Very thick steel
80
Why is the reactor core made of very thick steel?
To withstand high pressures and temperatures
81
In what is the reactor core?
A vessel
82
What is the vessel of the reactor enclosed by? What do they do?
Thick concrete walls. They absorb ionising radiation that escapes through the walls of the steel vessel
83
How do stars release energy?
Nuclear fusion
84
What is nuclear fusion?
The fusion of two like nuclei to form a larger nuclei i.e Hydrogen to Helium
85
Some of the mass of the small nuclei is converted into what?
Energy
86
What is some of the energy released by nuclear fusion transferred as?
Nuclear radiation
87
What is the heaviest element that can be created via nuclear fusion?
Iron
88
What is the Sun's core made of?
Plasma of bare nuclei; it has no electrons
89
What are some technical difficulties of making a fusion reactor?
Plasma of light nuclei has to be heated to very high temperatures and very high pressures
90
Why are high pressures and temperatures needed for fusion?
The nuclei needs enough kinetic energy to overcome the repulsive force of their positive charges
91
What would happen in a fusion reactor?
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
What is needed for a fusion reactor to be successful?
Has to release more energy than what is used to heat the plasma
93
What is the unit of measurement for radistion doses?
Sieverts (Sv) | Milisieverts (mSv)
94
List some causes of background radiation
``` Cosmic rays Ground & buildings Food & drink Natural radioactivity of the air Medical applications Nuclear weapon tests Air travel Nuclear power ```
95
Where are used fuel rods stored and for how long?
Big tanks of water for up to a year
96
What are used to open the fuel rods?
Remote control machines
97
What happens to the unused uranium and plutonium?
They are removed chemically from the used fuel and stored in sealed containers to be used again
98
Why does the remaining waste have to be stored in secures conditions?
To prevent radioactive contamination of the environment. | The isotopes have very long half lives.

AQA GCSE PHYSICS (2 decks)

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