P7 - Radioactivity Flashcards
(122 cards)
1
Q
What is activity?
A
The number of unstable atoms that decay per second in a radioactive source
2
Q
What is alpha radiation (α)
A
Alpha particles, each composed of 2 protons and 2 neutrons (helium nuclei), emitted by unstable nuclei at an extremely high speed
3
Q
What is an atomic number?
A
The number of protons (which equals the number of electrons) in an atom. It is sometimes called the proton number
4
Q
What is beta radiation (β)?
A
Beta particles that are high energy electrons created in, and emitted from, unstable nuclei
5
Q
What is a chain reaction?
A
Reactions in which one reaction causes further reactions, which in turn cause further reactions, etc.
6
Q
What is the count rate?
A
the number of decays recorded each second by a Geiger counter
7
Q
What is gamma radiation (γ)?
A
Electromagnetic radiation emitted from unstable nuclei in radioactive substances
8
Q
What is a half-life?
A
Average time taken for half the number of nuclei of the isotope (or mass of the isotope) in a sample to decay.
Average time for the count rate to fall by half
9
Q
What is ionisation?
A
Any process in which atoms become charged (become ions)
10
Q
What does irradiated mean?
A
Objects near a radioactive source are said to be irradiated by it. This simply means that they’re exposed to a radioactive source. This does not make the source radioactive.
11
Q
What are isotopes?
A
Atoms with the same number of protons and different numbers of neutrons
12
Q
What is the mass number?
A
The number of protons and neutrons in a nucleus
13
Q
What is a moderator?
A
Substance in a nuclear reactor that slows down fission neutrons
14
Q
What is nuclear fission?
A
The process in which certain unstable nuclei (such as uranium-235 and plutonium-239) split into 2 daughter nuclei, releasing energy (in the form of gamma radiation) and 2 or 3 neutrons as a result
15
Q
What is a nuclear fission reactor?
A
reactors that release energy steadily due to the fission of a suitable isotope, such as uranium-235 or plutonium-239
16
Q
What is nuclear fusion?
A
the process where light nuclei are forced together to fuse and form a larger nucleus
17
Q
What is radioactive contamination?
A
The unwanted presence of materials containing radioactive atoms on other materials. The contaminating atoms may then decay, releasing radiation which may cause harm. Contamination is especially dangerous as radioactive particles may get inside your body
18
Q
What is a reactor core?
A
The thick steel vessel used to contain fuel rods, control rods, and the moderator in a nuclear fission reactor
19
Q
How were radioactive materials discovered?
A
Henri Becquerel used covered photographic plates that were placed under uranium salts to discover radioactivity. Henri Becquerel’s work was expanded on by Marie and Pierre Curie, who investigated and discovered a range of new radioactive elements
20
Q
What is radiation?
A
The emission of energy as electromagnetic waves or as moving subatomic particles
21
Q
What is the unit for radioactivity (and count rate)?
A
Becquerels (Bq), where 1 Bq = 1 nuclear decay event per second
22
Q
What type of substances emit radiation?
A
Substances containing atoms with unstable nuclei
23
Q
What causes a nucleus to become unstable?
A
- If it contains too many protons
- If it contains too many neutrons
- If it is too large
These factors cause the nucleus to have excess energy, making it unstable
24
Q
Why does an unstable nuclei undergo nuclear decay/
A
An unstable nuclei can undergo nuclear decay, emitting radiation and becoming more stable as they do so.
25
What is a geiger counter?
A Geiger counter is a device that counts the number of radioactive particles per second. A Geiger counter clicks even when it is not near a radioactive source, this effect is due to background radiation
26
Why does a Geiger counter click even when it is not near a radioactive source?
Due to background radiation
27
Explain the gold foil experiment and the results it produced:
Rutherford set up a radioactive source which sent a beam of alpha particles towards a gold foil (which was surrounded by a detector which could detect alpha particles). Most of the alpha particles passed straight through the foil un deflected, this suggests that atoms are mostly empty space. Some of the alpha particles were deflected by small angles, this suggests the centre of the atom is positively charged as it repels the positively charged alpha particles. Occasionally, an alpha particle would travel back from the foil, this suggests the atom contains a dense centre containing a lot of mass
28
Why were so many atomic models abandoned in favour of new models?
New models explained data from tests and experiments better than old models, new results contradicted old results
29
What is a radioisotope?
An isotope which has an unstable nucleus. It will decay by emitting radiation
30
What is the difference between a daughter nucleus and the parent nucleus, when the parent nucleus has emitted alpha radiation?
The daughter nucleus would have an atomic mass of 4 less than the parent nucleus and an atomic number of 2 less than the parent nucleus
31
Write the equation for Thorium-232 decaying by emitting alpha-radiation (atomic number = 90)
32
Explain how Beta Decay occurs:
An atom decays into a new atom by changing a neutron into a proton and an electron. The fast moving, high energy electron is known as a beta particle
33
What is the difference between a daughter nucleus and the parent nucleus, when the parent nucleus has emitted beta radiation?
The daughter nucleus would have the same atomic mass, but the atomic number would increase by 1.
34
Write the equation for Radium-228 decaying by emitting beta-radiation (atomic number = 88)
35
What is the difference between a daughter nucleus and the parent nucleus, when the parent nucleus has emitted gamma radiation?
There is no atomic change within the nucleus
36
Explain the process of gamma decay:
Gamma radiation is surplus energy sometimes emitted after alpha or beta decay. The atom itself is not changed. Gamma radiation is part of the EM spectrum; a wave with a very high frequency, very short wavelength
37
What type of wave is gamma radiation?
An electromagnetic wave with a very high frequency, very short wavelength
38
Write the equation for when Radon 224 decays by alpha emission:
39
Write the equation for when Strontium 90 decays by beta emission
40
What is 1 bequerel?
1 decay event per second
41
What is the symbol for alpha radiation?
α
42
What is the symbol for beta radiation?
β
43
What is the symbol for gamma radiation?
γ
44
What is the range in air of alpha radiation?
5cm
45
What is the range in air of beta radiation?
1 metre
46
What is the range in air of gamma radiation?
unlimited - spreads out in air without being absorbed
47
What is the penetrative power of alpha radiation?
It can be stopped by a sheet of paper / skin
48
What is the penetrative power of beta radiation?
it can be stopped by 3mm of aluminium or a thin lead sheet
49
What is the penetrative power of gamma radiation?
It can be stopped by a thick lead sheet (several cm thick) or concrete (more than 1m thick)
50
What is the ionising power of alpha radiation?
Very strong ionising
51
What is the ionising power of beta radiation?
relatively ionising, less ionising than alpha but more ionising than gamma
52
What is the ionising power of gamma radiation?
Weakly ionising
53
What is ionising power?
The ability for nuclear radiation to remove electrons from atoms to form ions
54
Why is alpha radiation the most ionising?
Alpha particles are the most ionising because they have the largest mass and charge. Gamma rays do not interact with electrons strongly at all
55
Explain how ionising radiation is used in smoke alarms:
Smoke alarms contain a radioactive isotope that sends out alpha particles into a gap in a circuit in the alarm, The alpha particles ionise the air in the gap so there is a current across the gap. In a fire, smoke absorbs the alpha particles, preventing them from ionising the air, so the current across the gap drops and the alarm sounds. Beta or gamma radiation could not be used because they do not create enough ions to make the air in the gap conduct electricity, they would also not be absorbed by the smoke
56
Explain how ionising radiation is used in automatic thickness monitoring in metal foil:
Automatic thickness monitoring in metal foil production uses a radioactive source that sends out beta radiation. The amount of beta radiation passing through the foil depends on the thickness of the foil. The detector measures the amount of radiation passing through the foil. If the foil is too thick, the detector reading drops and the detector sends a signal to increase the pressure of the rollers on the metal sheet. This makes the foil thinner again. Gamma radiation isn't used because it would all pass through the foil unaffected. Alpha radiation isn't used as it would all be stopped by the foil.
57
What is the nuclear equation for alpha-decay?
58
What is the nuclear equation for beta-decay?
59
What happens to the activity of a source as more and more unstable atoms decay?
As there are fewer unstable atoms there is a lower activity as fewer unstable atoms decay per second
60
Radioactive decay is ..........................
* Random / Spontaneous
* Not effected by temperature
* Unpredictable
61
What is the half life of iodine-131?
8 days
62
What is the equation for count rate after "n" half lives?
Count rate after "n" half lives = Count rate before / 2ⁿ
63
What is the half life of carbon-14?
5760 years
64
What is the isotope used in carbon dating and why?
Carbon-14 as it is a radioisotope and decays over time
65
The half-life of a source of carbon-14 is 5760 years. After how many years will the number of radioactive particles be 12.5% of the original amount?
17280
66
The half life of radon-222 is 3.8 days. If the original amount of this source was 2400 Bq, what do you expect it to be after 15.2 days?
150 Bq
67
What are the 4 medical applications of radioisotopes?
* Radioactive tracers
* Gamma cameras
* External Radiotherapy
* Internal Radiotherapy
68
Explain how radioactive tracers work
Radioactive tracers are used to trace the flow of a substance through an organ and therefore image and diagnose a range of illnesses. The tracer contains a radioactive isotope that emits gamma radiation as it can be detected outside the system. For example, doctors use radioactive iodine to find out if a patients kidney is blocked.
Before the test, the patient drinks water containing a tiny amount of the radioactive substance. A detector is then placed against each kidney. Each detector is connected to a chart recorder.
*The radioactive substance flows in and out of a normal kidney. So the detector reading goes up then down.
*For a blocked kidney, the reading goes up and stays up. This is because the radioactive substance goes into the kidney but does not flow out again
69
What radioisotope is used in radioactive tracers and why?
Iodine-131 is used because:
* Its half life is eight days, so it lasts long enough for the test to be done, but decays almost completely after a few weeks
* It emits gamma radiation, so it can be detected outside the body
* It decays into a stable product
70
Explain how gamma cameras work:
Gamma cameras are used to take images of internal body organs. Before an image is taken, the patient is injected with a solution that contains a gamma-emitting radioactive isotope. The solution is then absorbed by the organ, and a nearby gamma camera detects the gamma radiation emitted by the solution. The gamma rays pass through the holes in the thick lead grid in front of the detector (this way only gamma rays from nuclei directly in front of the detector are detected as rays at an angle are blocked by the lead grid). The detector signals are used to build up an image of where the radioactive isotope is located in the organ.
71
Explain how external radiotherapy works:
Gamma radiation in a narrow beam is sued to destroy cancerous tumours. The radiation is emitted from a radioactive isotope of cobalt. It has a half-life of 5 years. Gamma radiation is used because it can penetrate deeper into the body than beta radiation and alpha radiation
72
Explain how internal radiotherapy works:
radioactive implants are used to destroy cancer cells in some tumours. 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 that most of the unstable nuclei will have decayed soon afterwards
73
What is the natural radiation that is all around us known as?
background radiation
74
Why is it not possible to know when a nucleus will decay?
Because nuclear decay is random and uncontrollable
75
What is the activity of a radioactive material that emits 400,000 particles over a period of 20 minutes?
333.3 Bq
76
What are the 2 types of nuclear fission?
* Spontaneous
| * Induced
77
What is spontaneous nuclear fission
fission is unforced and happens by itself, this is rare
78
What is induced nuclear fission?
If an already unstable nuclei absorbs a neutron, it's atomic mass will increase and it will become even more unstable and fission will occur, this is usually how fission occurs
79
What types of atoms can undergo nuclear fission?
Not all atoms can undergo nuclear fission, those that can are called fissionable
80
Explain how a chain reaction can occur in nuclear fission:
During fission, neutrons (fission products) fired form a nucleus can collide with other unstable nuclei, causing further fission events to occur, resulting in a chain reaction
81
What is the purpose of control rods in a nuclear reactor?
Control rods absorb excess neutrons, this prevents the chain reaction becoming out of control
82
What are the technical difficulties with making fusion a useful source of energy?
* High pressure and temperature is required
| * The nuclei repel each other as they are both positively charged
83
What releases more energy, nuclear fission or nuclear fusion?
Both release lots of energy, but nuclear fusion releases much more energy than nuclear fission
84
What is the equation for this nuclear fusion reaction?
85
What is the equation for this nuclear fusion reaction?
86
What is the equation for this nuclear fusion reaction?
87
What is background radiation?
Background radiation is a measure of the level of ionising radiation present in the environment at a particular location which is not due to deliberate introduction of radiation sources. Background radiation orignates form a variety of sources, both natural and artificial
88
Why does radioactive waste need to be stored securely and for many years?
To prevent radioactive contamination of the environment and it needs to be stored for many years as the waste contains radioisotopes with long half lives
89
Why is it difficult making nuclear fusion a useful source of energy?
Nuclei approaching each other will repel each other as they are both positively charged. To overcome this, the nuclei must be heated to extremely high temperatures to give them enough kinetic energy to overcome this repulsion, and fuse together. Because of the enormously high temperatures involved, the reaction cannot take place inside a normal container, since the nuclei would touch the edges and grow cold, causing fusion to stop. Instead, the fusion reaction must be contained by a magnetic field. This is extremely difficult and expensive to perform.
90
What are the most common sources of background radiation?
* Cosmic rays
* Ground and buildings
* Food and drink
* Natural radioactivity in the air
* Medical applications
* Air travel
91
How is nuclear waste dealt with?
Used fuel rods are removed from a reactor and stored in big tanks of water for up to a year to cool down. Remote-control machines are then used to open up the fuel rods. The unused uranium and plutonium is removed chemically so that it can be reused. The material that is left contains lots of radioactive isotopes with long half lives. This radioactive waste has to be stored in secure conditions for many years to prevent radioactive contamination of the environment
92
What does it mean if a substance is radioactive?
if the substance contains atoms that decay, releasing radiation in the form of particles or energy
93
How do you reduce the effect of irradiation?
* Keeping sources in a lead-lined box
* Standing behind barriers or being in a different room
* Using remote-controlled arms
94
How do you reduce the effects / avoid radioactive contamination?
* Gloves and tongs should be used when handling sources, to avoid particles getting stuck to your skin or under your nails
* Using protective suits to stop particles being breathed in
95
Is irradiation or contamination the main concern when working with alpha particle emitting sources?
Contamination, this is because alpha particles can only travel a few centimetres in the air and cannot penetrate your skin and cause damage to your internal organs but can cause great damage if already inside your body
96
Explain the seriousness of irradiation and contamination outside the body:
Outside the body, beta and gamma sources are the most dangerous. This is because beta and gamma particles can penetrate the body and get to the delicate organs. Alpha is less dangerous because it cannot penetrate the skin and is easily blocked by a small air gap as it can only travel a few centimetres in the air. High levels of irradiation from all sources are dangerous, especially from beta and gamma emitting sources
97
Explain the seriousness of irradiation and contamination inside the body:
Inside the body, alpha sources are the most dangerous, this is because they do all their damage in a very localised area. So contamination, rather than irradiation, is the main concern when working with alpha sources. Beta sources are less damaging inside the body, as radiation is absorbed over a wider area, and some passes out of the body all together. Gamma sources are the least dangerous inside the body, as they mostly pass straight out - they have the lowest ionising power
98
What are the risks of irradiation?
* Radiation can enter living cells and ionise atoms and molecules within them. This can lead to tissue damage
* Lower doses tend to cause minor damage without killing the cells. This can cause mutations which cause the cells to divide uncontrollably. This is known as cancer
* Higher doses tend to kill cells completely, causing radiation sickness (leading to vomiting, tiredness and hair loss) if a lot of cells all get irradiated at once
99
How do unstable nuclei become stable?
Nuclear decay
100
What is the mass, atomic number, and charge of an alpha particle?
```
mass = 4
number = 2
charge = +2
```
101
what is the mass and charge of a beta particle?
```
mass = almost 0
charge = -1
```
102
What is the equation for number of unstable nuclei after "n" half lives?
number of unstable nuclei after "n" half lives = initial number of unstable nuclei / 2ⁿ
103
What does fission release?
* 2 or 3 high speed neutrons
| * energy - in the form of gamma radiation, and kinetic energy of the nuclei and neutrons
104
Why is a moderator needed to slow high-speed neutrons in a nuclear reactor?
slower moving neutrons are more effective in causing a fission event, faster moving neutrons don't cause further fission
105
How does fusion release energy
During fusion, some of the mass of the small nuclei is converted to energy (this is given by the equation "E = mc²)
106
How is nuclear fission brought about?
When 2 light nuclei collide at very high speeds
107
How would workers who work with radioactive materials reduce risk of exposure to radiation?
Wear a personal radiation monitor, such as a film badge. This badge shows if it is over-exposed to ionising radiation, its wearer should not continue to work with radioactive equipment for a period of time
108
What fuel do nuclear reactors use?
Enriched uranium, 97% Uranium-238 (non-fissionable), 3% Uranium-235 (Fissionable)
109
Explain how nuclear fission reactors work:
The reactor core contains the fuel rods, control rods, and water at high pressure. The fission neutrons are slowed by collisions with the atoms in the water molecules. This is because fast neutrons don't cause further fission of U-235. The water is said to act as a moderator as it slows the fission neutrons. Control rods absorb surplus neutrons. This keeps the chain reaction under control. The depth of the rods in the core is adjusted to maintain a steady chain reaction. The fuel rods become very hot (due to energy released during fission) and the water acts as a coolant. Its molecules' kinetic energy stores increase as energy is transferred from the neutrons and fuel rods. The water is pumped through the core. Then it goes through sealed pipes to and from a heat exchanger outside the core. The water transfers energy from the core to the heat exchanger. In the heat exchanger the moderating water heats and evaporates water in pipes which drives a turbine, which in turn drives a generator, generating electricity
110
How is plasma heated and contained in a fusion reactor?
* Heated by passing a large electrical current through it
| * Contained by a magnetic field so that it does not touch the reactor walls
111
Why is fusion a better energy potential source than fission?
* The fuel for fusion reactors is easily available as heavy hydrogen is naturally present in sea water (unlike fission which requires uranium-235)
* The reaction product, helium, is a non-radioactive gas, so it is harmless (whereas fission produces radioactive waste)
* Fusion releases much larger amounts of energy than fission does
112
What are 5 nuclear issues?
* Background radiation
* Nuclear waste
* Nuclear accidents
* Half-lives and instability
* Radioactive risks
113
What is heavy hydrogen?
Another term for the hydrogen isotope deuterium, it has a mass number of 3 (contains 1 proton and 2 neutrons)
114
What is background radiation?
A Geiger counter clicks even without a radioactive source near it. This is because of background radiation. Background radiation is a measure of the level of ionizing radiation present in the environment at a particular location which is not due to deliberate introduction of radiation sources
115
Explain what Background Radiation is mostly caused by.
Background radiation in the air is mostly caused by radon gas that seeps through the ground from radioactive substances in rocks deep underground. Radon gas emits alpha particles, so radon is a health hazard if it is breathed in. It can seep into homes and other buildings in some locations. In affected homes, pipes under the building can be installed and fitted to a suction pump to draw the gas out of the ground before it seeps into the building
116
Explain how nuclear waste is a nuclear issue and how it is dealt with.
Used fuel rods are extremely hot and very radioactive. After they are removed from a reactor, they are stored in big tanks of water for up to a year. The water cools the rods down. Remote-control machines are then sued to open up the fuel rods. The unused uranium and plutonium are removed chemically from the used fuel. These are stored in sealed containers so they can be used again. The material that's left contains lots of radioactive isotopes with long half-lives. This radioactive waste has to be stored in secure conditions for many years to prevent contamination of the environment
117
Explain how nuclear accidents are a nuclear issue and how it is dealt with.
In 1986, a nuclear reactor in Ukraine exploded. A cloud of radioactive material from the fire drifted over many parts of Europe, including Britain. More than 100 000 people were evacuated and over 30 people died in the accident. More have developed leukaemia or other cancer types since then. The Chernobyl reactor did not have high-speed shutdown systems like most reactors have, safety instructions were ignored. Lessons learnt were put into place during the Fukushima meltdown, the population within 20km were evacuated and many things were monitored for years to come.
118
Explain how third-generation nuclear reactors could differ from old nuclear reactors:
* A standard design to reduce costs and construction time
* A longer operating life
* More safety features, such as convection of outside air through cooling panels along the reactor walls
* Much less effect on the environment
119
Explain how the half life an instability of a nuclei is a nuclear issue:
Radioactive isotopes have a wide range of half-loves. Some radioactive isotopes have half-lives of a fraction of a second, whilst others have half-lives of over 1 billion years. Isotopes with the shortest half-lives have the most unstable nuclei - so they emit a lot of radiation in a short amount of time
120
Why does the hazards caused by the ionising effect of radiation from radioactive materials decrease over time?
The half-life of a radioactive source tells you how quickly its activity decreases. As its activity decreases, the rate it gives out radiation decreases. So the hazards caused by the ionising effect of the radiation from radioactive materials decrease with time according to the half-lives of their isotopes.
121
Why are gamma rays weakly ionising?
They do not interact with the atoms much, they tend to pass straight through
122
Is it safe to eat irradiated food?
Yes, irradiating food does not make it radioactive, it simply kills the hsrmful bacteria and other pathogens that may be on the food
