Atoms & Radioactivity for EOY10 exam Flashcards
1
Q
Examples of nucleons?
A
Protons and neutrons
2
Q
What is the majority of the mass of an atom?
A
The nucleus, as the mass of an electron is almost zero compared to the mass of protons and neutrons
3
Q
What was Thomson’s theory about the atom?
A
1904 - Plum Pudding Model
4
Q
What was Rutherford’s theory about the atom?
A
1911 - Nuclear Model; that most of the mass of the atom was concentrated in the nucleus which carries a positive charge
5
Q
What was Bohr’s theory about the atom?
A
1913 - Bohr’s model, electrons orbit nucleus in certain energy levels
6
Q
What was Chadwick’s theory about the atom?
A
1932 - discovered the neutron
7
Q
Which was the first sub-atomic particles to be discovered?
A
The electron, by Thomson
8
Q
What was the Plum Pudding Model?
A
A sphere of positive charge (dough) with electrons dotted inside (plums)
9
Q
What did the discovery of the electron show about atoms?
A
That atoms were not the smallest thing, as the electron was smaller than the atom
10
Q
What did the Bohr model show?
A
- That electrons can only orbit the nucleus in certain energy levels
- Electromagnetic energy is emitted from the atom if an electron jumps from an excited energy level to one that’s closer to the nucleus
- If an electron absorbs energy it can jump to a higher energy state from the nucleus
11
Q
What did later experiments suggest about the atom?
A
- the positive charge of any nucleus could be subdivided into a whole number of smaller individual sub-atomic particles called protons
- 1934 - Chadwick used alpha scattering experiment to provide evidence for existence of the neutron
12
Q
Who was the first to call the nucleus of a hydrogen atom a proton?
A
Rutherford
13
Q
In the scattering experiment, how could have the alpha particles been supplied and been moving in the right direction?
A
From radioactive matter. Surrounded by lead shielding apart from a small opening facing the way they wanted the beam
14
Q
What happens when isotopes have unstable nuclei?
A
They break down or disintegrate
15
Q
What happens when isotopes break down or disintegrate?
A
They give out radiation said to be radioactive
16
Q
What is the process when isotopes with unstable nuclei disintegrate?
A
Radioactive decay
17
Q
What may nuclear radiation be?
A
- an alpha particle
- a beta particle
- a gamma ray
- a neutron
18
Q
What does an alpha particle consist of?
A
2 neutrons and 2 protons - the same as a helium nucleus
19
Q
What is a beta particle?
A
When a high speed electron is ejected from the nucleus as a neutron changes into a proton
20
Q
What is a gamma ray?
A
High energy electromagnetic radiation from the nucleus
21
Q
What are nuclear equations used to represent?
A
Radioactive decay
22
Q
What happens to the mass and charge of the nucleus during alpha decay?
A
Both the mass and charge of the nucleus decease
23
Q
What happens to the mass and charge of the nucleus during beta decay?
A
The mass of the nucleus doesn’t change however the charge of the nucleus increases
24
Q
What happens to the mass and charge of the nucleus during gamma decay?
A
The emission of a gamma ray doesn’t cause the mass or charge of the nucleus to change
25
What is an ion?
An atom which has lost or gained an electron
26
What happens when radioactive radiation strikes atoms in a substance?
They can knock an electron from one atom to another
27
Properties of alpha particles?
* Relatively big, heavy and slow moving
* Large relative charge (+2)
* Strongly ionising - bash into lots of atoms and knock electrons off them
28
Properties of beta particles?
* Quite small and move quite fast
| * Moderately ionising because they have a smaller relative charge (-1)
29
What is the relative charge of an alpha particle?
+2
30
What is the relative charge of a beta particle?
-1
31
Properties of gamma radiation?
Weakly ionising as gamma is not charged
32
What is the range of alpha in air?
A few cm
33
What is the range of beta in air?
A few metres
34
What is the range of gamma in air?
Infinite
35
What can alpha radiation be stopped (absorbed) by?
Paper, card, skin
36
What can beta radiation be stopped (absorbed) by?
Sheet of aluminium (5mm)
37
What can gamma radiation be stopped (absorbed) by?
Thick sheet of lead or metres of concrete
38
Which type of radiation is most ionising?
Alpha
39
Which type of radiation is least ionising?
Gamma
40
What is the safest type of radiation to have inside the body?
Gamma as it's the least ionising and escapes easily
41
What is the most dangerous type of radiation to have inside the body?
Alpha as it's most ionising and cannot escape
42
What is the safest type of radiation to have outside the body?
Alpha as it's least penetrating
43
What is the most dangerous type of radiation to have outside the body?
Gamma as it's most penetrating
44
What is alpha used in?
Smoke detectors
45
How do smoke detectors work?
Alpha ionises air particles causing a current to flow. If there is smoke in the air, the smoke binds to the ions reducing the number available to carry a current. Current falls and alarm sounds
46
Why is alpha used in smoke detectors?
* Ionising
* Charged
* Cannot penetrate though a plastic shield
* Can be absorbed by smoke
* Shortest range
47
Why aren't beta or gamma used in smoke detectors?
They are less ionising and have a larger range
48
Are smoke detectors safe given they contain alpha particles?
Yes as alpha has a short range and not penetrating, provided it is not pulled apart
49
What is beta used in?
Beta emitters test the thickness of thin sheets of metal
50
Why is beta used to test thickness of metal?
Particles are not immediately absorbed by the material like alpha, and do not penetrate as far as gamma
51
What is gamma used for?
* Tracers in medicine
* Radiotherapy
* Food irradiation
52
How is gamma used for tracers in medicine?
Gamma radiation should be emitted from the source injected into the patient, so it can be detected outside the body
53
Why isn't alpha used for tracers in medicine?
Would be too dangerous as the ionisation it causes could mutate cells and cause cancer
54
How is beta used for leak detection in pipes?
The radioactive isotope is injected into the pipe. The outside of the pipe is checked with a Geiger-Muller detector to find areas of high radioactivity - where the pipe is leaking
55
Why is beta used for leak detection in pipes?
It has a short half life so the material doesn't become a long term problem. It has to be detected through the metal as well as the earth
56
Why is gamma used in radiotherapy?
Gamma kills cancer cells
57
Why is gamma used in food irradiation?
Because gamma keeps it fresh for longer as it kills bacteria or fungi
58
What is the half life of a radioactive isotope?
• The average time it takes for the number of nuclei of the isotope in a sample to half
59
What is the net decline of a radioactive sample?
The fraction of nuclei that have decayed in a certain time
60
How is the net decline of a radioactive sample measured?
Fraction, ratio, percentage
| doesn't have a unit
61
What did Rutherford expect the alpha particles to do in the scattering experiment? Why?
He expected them to go through the thin sheet of atoms easily because they were moving at a very high speed
62
What was the material of the sheet of atoms in the scattering experiment?
Gold
63
What was Rutherford expecting to observe in the scattering experiment? Why?
For slight changes in the direction of the alpha particles due to them repelling from the thinly spread positive material of the atoms
64
When does a nucleus become unstable?
When it possesses either too many or too few neutrons compared to the number of protons
65
What is radiation detected with ?
A Geiger counter
66
How is nuclear radiation used in medicine for imaging?
* radioactive tracers - imaging flows
| * gamma cameras - imaging internal organs
67
What do radioactive tracers image?
Flows inside the body
68
What do gamma cameras image?
Internal organs
69
Why is imaging using radioactive radiation important?
To help with diagnosis
70
Why is nuclear radiation used in medicine?
For treatment; to destroy cancer cells
71
What processes using nuclear radiation help with diagnosis?
* radioactive tracers
| * gamma cameras
72
How do radioactive tracers work?
* a small amount of radioactive material is put into the patients body
* tracer is given time to move through body
* radioactive detector is positioned to detect radiation outside the body
* multiple images are taken to show progress of tracer over time
73
What type of radiation is used in medical tracing?
Gamma
74
Why is gamma used in medical tracing?
It is the least ionising and the most penetrating, meaning it can leave the body eventually
75
Why isn't alpha used in medical tracing?
It can't be detected outside the body and is very ionising so would damage cells as it moved through the bloody
76
What are the properties of gamma that ensure medical tracing is not harmful to the patient?
Gamma is not ionising, has a short half life and is not toxic
77
What does a gamma camera do?
Images internal organs
78
How does a gamma camera work?
* a radioactive isotope (gamma emitting) is objected into the patient
* the isotope concentrates in the organ
* a gamma camera is positioned over the area emitting gamma
79
What does ionising mean?
When atoms are turned into ions by losing or gaining electrons
80
What can ionising radiation do to cells?
Low doses - damage cells
High doses - destroy cells
This can lead to cancer
81
How are cancer cells destroyed in a tumour?
Gamma radiation in narrow beams
82
What is irradiation?
When the radiation stops as soon as the source of radiation has been removed
83
Example of irradiation?
When a light is turned on the room is filled with electromagnetic radiation (visible light). When the light is turns off the electromagnetic radiation is gone
84
What is contamination?
When the source of ionising radiation is transferred
85
Example of contamination?
When radioactive isotopes in solids, liquids or gases are introduced into the environment
86
What is nuclear fission?
The splitting of a large nucleus into two smaller nuclei ('daughters') while releasing energy
87
Which nuclei are split in fission reactions?
Usually uranium-235 but also plutonium-239
88
What is induced fission?
When a reaction occurs due to a neutron being fired at a uranium nucleus
89
What do fission reactions release?
* two or three neutrons at high speeds (these are used in further reactions)
* energy in the form of radiation and kinetic energy of the fission neutrons
90
What form of energy is released in fission?
* radiation
| * kinetic - of the neutrons and the fragment nuclei
91
How is the output of a nuclear fission power station made stable?
The energy released must be constant and not grow rapidly like in an uncontrolled chain reaction
92
In a nuclear reactor, what is the function of the control rods?
To absorb surplus neutrons to keep chain reaction under control
93
In a nuclear reactor, what is the function of the moderator?
To slow the fission neutrons down
94
Why is water used as a moderator in a nuclear reactor?
Fission neutrons are slowed down by collisions with the atoms in the water molecules
95
What is a fission neutron?
A neutron released when a nucleus undergoes nuclear fission
96
In a nuclear reactor, what is the function of the coolant?
Water - transfers heat so radioactive water is not turned to steam
97
In a nuclear reactor, why is the reactor core in a thick steel vessel surrounded by concrete walls?
To withstand high temperature and pressure. Walls absorb gamma radiation that escapes steel vessel
98
In a nuclear reactor, why does the coolant circulate through sealed pipes to and from a heat exchanger?
So contaminated water is not turned to steam and enters the atmosphere
99
In a nuclear reactor, why may the control rods need to be inserted completely into the reactor core?
So there isn't too much energy being released from uncontrolled fission
100
What is nuclear fusion?
When two small nuclei collide and fuse to form a larger nucleus, releasing energy
101
What process powers the sun and the stars?
Nuclear fusion
102
What happens when the gas in a fusion reactor gets very hot?
It forms a plasma of small nuclei
103
How is the plasma contained in a fusion reactor?
Using a magnetic field to prevent it from touching the container walls
104
What is one of the products when hydrogen nuclei fuse?
Helium
105
What happens in a fusion reactor if the plasma touches the sides of the container?
The plasma would cool down, and fusion would stop
106
In fusion, what do nuclei need to fuse?
Enough kinetic energy
107
In fusion, what happens if nuclei do not have enough kinetic energy to fuse?
They will repel each other and not fuse
108
Advantages of nuclear fission?
* concentrated source of energy
* no polluting gases - energy is released from nuclear reactions not combustion
* supply of uranium for many years
* reliable - 24/7 (doesn't depend on weather like renewables)
109
Disadvantages of nuclear fission?
* produces radioactive waste
* chain reaction must be controlled
* non-renewable
110
Advantages of nuclear fusion?
* produces very little radioactive waste - safer
* no chain reaction to control - safer
* even more concentrated energy
* fuel readily available (hydrogen in water)
* renewable
* hydrogen is cheap
111
Disadvantages of nuclear fusion?
• not yet viable - fusion on earth needs more energy input than output (need 5 million amp current!)
112
Which is a more concentrated source of energy: fission or fusion?
Fusion
113
Which type of nuclei fuse in the sun?
Hydrogen
114
Which type of nuclei are formed in the sun?
Helium
