Topic 6 – Radioactivity Flashcards
(98 cards)
1
Q
Describe an atom
A
- Positively charged nucleus, consisting of protons and neutrons, surrounded by negatively charged electrons,
- Nuclear radius much smaller than that of the atom
- Almost all of the mass in the nucleus
2
Q
What is an isotope of an atom
A
Atom of an element that has different number of neutrons but same number of protons. Isotopes of an atom have the same atomic number but different mass number
3
Q
What is the charge of a nucleus of an atom
A
Positive
4
Q
What is the relative mass of a proton
A
1
5
Q
What is the relative mass of a neutron
A
1
6
Q
What is the relative mass of an electron
A
1/1836
7
Q
What is the relative mass of a positron
A
1/1836
8
Q
What is the relative charge of a proton
A
+1
9
Q
What is the relative charge of an electron
A
-1
10
Q
What is the relative charge of a neutron
A
0
11
Q
What is the relative charge of a positron
A
+1
12
Q
Why is an atom neutral
A
Number of protons equals number of electrons
13
Q
How do electrons orbit nucleus of an atom
A
Electrons orbit nucleus at different set distances from the nucleus
14
Q
How does an atom’s electron arrangement changes orbit when it absorbs EM radiation
A
- Electrons move to higher energy levels
- Move away from nucleus
15
Q
How does an atom’s electron arrangement changes orbit when it emits EM radiation
A
- Electrons move to lower energy level
- They move towards nucleus
16
Q
How do atoms form positive ions
A
By losing their outer electrons
17
Q
What are types of radiatoi emitted from unstable nuclei in a random process
A
- Alpha
- Beta minus
- Beta plus (Positron)
- Gamma Rays
- Neutron
18
Q
What types of radiation are ionising
A
- Alpha
- Beta minus
- Beta plus (positron)
- Gamma
19
Q
What is meant by background radiation
A
- Radiation that is always present
- It is in very small amounts and so not harmful
20
Q
Give sources of background radiation
A
- Rocks
- Cosmic rays from space
- Nuclear weapon testing
- Nuclear accidents
21
Q
How do you measure and detect radioactivity
A
- Using a photographic film
- Using a Geiger-Müller tube
22
Q
How is a Geiger-Muller used to measure radioactivity
A
- When Geiger-Müller tube absorbs radiation it produces a pulse, machine uses pulse to count amount of radiation
- Frequency of pulse depnds on how much radiation is present
- High frequency means tube is absorbing large amount of radiation
23
Q
What makes up an alpha particle
A
Helium nucleus (2 protons and 2 neturons)
24
Q
What is a beta particle
A
Electron
25
What is a gamma ray
An electromagnetic radiation
26
What is the range of an alpha particle through air
A few centimetres
27
What is range of beta radiation
Few metres
28
What is the range of gamma radiation
Many km
29
What will block Alpha radiation
Paper
30
What will block beta radiation
Aliminium Foil
31
What will block gamma radiation
Thick lead sheets
32
What is charge of alpha particles
+2
33
What is the charge of beta particles
-1
34
What is the charge of gamma radiation
0
35
What is the relative atom mass of alpha particles
4
36
What is the relative atomic mass of beta particles
1/1835
37
What is the relative atomic mass of gamma radiation
0
38
Which type of radiation has the most ionising power
Alpha
39
Which type of radiation has the least ionising power
Gamma
40
Which type of radiation has the greatest penetrative power
Gamma
41
Which type of radiation has the least penetrative power
Alpha
42
Describe the plum-pudding model of the atom
Sphere of positive charge with negatively charged electrons distributed evenly throughout it
43
Before the discovery of the electron, what was believed about the atom
It was indivisible
44
Which expirement led to the plum-pudding model being droped
Rutherford's alpha-scattering experiment
45
What is the name given to the currently accepted model of the atom
The Bohr model
46
Describe Rutherford's alpha-scattering experiment
* Alpha particles (+2 charge) were fired at thin sheet of gold foil
* Most particles went straight through
* Some particles were deflected by acute angles
* Few particles were deflected by obtuse angles
47
What happens when alpha particles interact with a magnetic field
It deflects
48
What happens when beta particles interact with a magnetic field
It deflects
49
What happens when gamma radiation passes through a magnetic field
It passes through (No deflection)
50
What are the conclusions of Rutherford's alpha-scattering experiment
* Most of an atom is empty space
* The nucleus has a positive charge
* Most of the mass of an atom is concentrated in the nucleus
51
What is the Bohr model
* Niel Bohr added to rutherford's model saying electrons orbit the nucleus at fixed distances or at different energy levels
* When atoms gain or lose energy they move up or down the energy levels
52
Describe the process of beta minus decay
Neutron becomes a proton plus a electron
53
Describe the process of beta plus decay
Proton becomes a neutron plus a positron
54
What happens to the atomic number and mass number of an atom when alpha decay occurs
* Atomic number decreases by 2
* Mass number decreases by 4
* New element is made since atomic number has changed
55
What happens to the atomic number and mass number of an atom when beta minus decay occurs
* Mass number stays same as total number of neutrons and protons hasn't changed (one has just turned into another)
* Atom number increases since there is one more proton
* New element is formed as atomic number has changed
56
What happens to the atomic number and mass number of an atom when beta plus decay occurs
* Mass number remains same
* Atomic number increases by one
* New element is formed as atomic number has changed
57
What happens to the atomic number and mass number of an atom when neutron decay occurs
* Mass number of nucleus decreases by one
* Atomic number remains same
58
What happens to the atomic number and mass number of an atom when gamma decay occurs
* Atomic number remains same
* Mass number remains same
59
What often happens to nuclei that have undergone radioactive decay
Often undergo nuclear rearrangement and lose energy as gamma radiation
60
What is the unit for the activity a radioactive isotope
Becquerel, Bq
61
What is the half life of a radioactive isotope
Time taken for half undecayed nuclei to decay or activity of source to decay by half
62
Describe how the activity of a radioactive source decreases
over a period of time
Unestable nuclei transform into stable ones by emitting radiation
63
What can be said about the half life and radioactive decay of a radioactive isotope
* Can not be predicted when a particular nucleus will decay (Random process)
* Half-life enables activity of very large number of nuclei to be predicted during decay process (number of nuclei to be decayed can be predicted with high numbers of nuclei)
64
What are uses of radioactivity
* Household fire (smoke) alarms
* Irradiating food
* Sterilisation of equipment
* Tracing and gauging thickness
* Diagnosis and treatment of cancer
65
How is radiation used in househould fire (smoke) alarms
* Radioactive substance in alarm emits alpha radiation
* Emitted alpha particle ionises air in detecter causing a current to flow between plates
* When smoke interferes with the radiation, air is no longer ionised and so no current can flow
* This reduction in current flow triggers alarm
66
How is radiation used in irradiating food
* Can be used to preserve fruit sold in supermarkets by exposing fruit to radioactive source
* Gamma rays emitted will destroy bacteria on fruit but not change it in significant way
67
How is radiation used in sterilisation of equipment
Radiation (usually gamma) is exposed onto equipment to kill all microbes present on equipment so they are safe for operations
68
How is radiation used in tracing and gauging thickness
* Most commonly beta particles
* Used to measure thickness of thin materials such as paper, cardboard or aliminium foil
* As material moves above/below beta source, particles able to penetrate material can be monitored using detector
* If material gets thicker, more particles will be absorbed, meaning less will get through
* If material gets thinner, less particles will be absorbed, meaning more will get through
* This allows machine to make adjustments to keep thickness of material constant
69
How is radiation used in diagnosis and treatment of cancer
* Radiotherapy is name given to treatment of cancer using radiation
* Radiation can kill living cells, some cells such as bacteria and cancer cells are more susceptible to radiation than others
* Beams of gamma rays are directed at cancerous tumour. Gamma rays are used as they can penetrate body and reach tuumor.
* Beams are moved around to minimise harm to healthy tissue whilst still being aimed at tumour
* Tracer is radioactive isotope that can be used to track movement of substances like blood around body. A PET scan can detect emissions from tracer to diagnose cancer and determine location of tumour
70
Why is ionising radiation dangerous
* It can damage tissue and kill cells
* It can cause cell mutations
71
What precautions should people take when using ionising radiation
* Avoid handling source directly (use tongs)
* Wear radiation protective clothing
* Keep the radiation in lead containers to reduce amount of radiation that can escape
* Keep exposure time to minimum
72
Does a long half life or short half life make a radioactive source more dangerous
Long half life, it would remain highly radioactive for longer making it more dangerous
73
What precautions are taken to ensure safety of people exposed to radiation
* Limiting dose for patients
* Limit risks for medical personell (e.g. wear protective clothing)
* Use radiation with short half life so it wont remain highly radioactive for long. Reduces risk to doctors and patienta
74
What is radioactive contamination
Presence of unwanted radioactive nuclei on other materials
75
What is irradiation
Process of exposing material to nuclear radiation, material does not become radioactive
76
What is the difference between contamination and irradiation
Contamination is presence of unwanted radioactive nuclei on other materials whereas radiation is process of exposing material to nuclear radiation, material does not become radioactive
77
How is a radioactive tracer used in medicine
* Tracer is placed inside body (can be in drink, eaten or injected)
* Tracer releases gamma radiation which is detected by detector which moves around body
* Can be used to produce picture of patient's body
78
How does a PET scanner work
* PET uses a tracer injected into patient's body
* Scanner detecte gamma rays releaced by tracer
* Multiple images are taken and this is used to form 3D image of patient's body
79
Isotopes are used in PET scanners. What is important about where they are produced and why
The must be produced near the hospital because the isotopes used have short half life so must be used soon after production
80
Compare and contrast the treatment of tumours using
radiation applied internally or externally
* Internally, small pellets of radioactive materials can be inserted into tumour exposing it directly to radiation
* Externally, beams of gamma rays are directed at cancerous tumour, surrounding healthy tissue tends to be shielded to avoid causing any damage
81
What are the advantages of using nuclear power for generating electricity
* Do not produce carbon dioxide
* The fuel is readily available, would reduce strain on fossil fuel supplies
* Less nuclear fuel has to be used to produce same amount of energy as burning fossil fuel
* Does not contribute to global warming
82
What are the disadvantages of using nuclear power to generate electricity
* Unpopular - public perceive nuclear power as very dangerous
* Security risks as radioactive substances can be useful for terrorists
* Expensive to commission and decommission stations - which may be bad for a country's economy
* Radioactive waste can be difficult to dispose of and will remain radioactive for many years - can be dangerous to humans and environment
* Risk of nuclear accidents
83
What is nuclear fission
Splitting of large, unstable nuclei to form two daughter nuclei and emission of two or more neutrons accompanied by release in energy. It happens when a slow moving neutron collides with the unstable nucleus
84
What types of nuclear reactions can be sources of energy
Nuclear reactions including fission fusion and radioactive decay can be source of energy
85
What is produced in nuclear fission reactions
* Two or three neutrons
* Two smaller nuclei
* Gamma rays (nuclear fission is radioactive)
* Energy
86
What nuclei is often used for nuclear fission
Uranium-235
87
What takes place during a chain reaction in a nuclear reactor
* Unstable nucleus absorbs neutron
* Nucleus undergoes fission and releases 2 or 3 further neutrons
* These induce more fission which results in chain reaction
88
What is the consequence of an uncontrolled chain reaction
* Rate of fission events becomes too high and results in production of too much energy
* Can lead to nuclear explosion
89
What are the three main components of the core of a nuclear reactor
* Fuel rods
* Control rods
* Moderator
90
How is the chain reaction in a fission reactor kept under control
* Control rods positioned in between fuel rods
* Rate of fission controlled by moving rods up and down
* Lower rods are inserted slower rate of fission
91
What is role of moderator in nuclear reactor
To slow down neutrons so they are travelling at speeds which allow them to be absorbed by fissile nuclei and cause fission
92
How is electricity produced in nuclear power station
* Reactions release thermal energy
* Thermal energy is used to boil water and produce steam
* Steam used to turn turbine which starts generator
93
What is nuclear fusion
Creation of larger nuclei resulting in loss of mass from smaller nuclei accompanied by release of energy
94
Why does nuclear fusion not happen at low temperatures
Both nuclei are positive so lot of energy required to overcome electrostatic repulsion of protons
95
Does nuclear fusion or nuclear fission produce more energy
Nuclear fusion
96
Give an example of where nuclear fusion occurs
In stars - stars use fusion as main source of energy
97
Why do the conditions for fusion make it difficult to create a practical and economic form of power station using fusion
Fusion requires very high temperatures and pressure which requires a lot of energy to do so, currently production of fusion results in net loss of energy
98
How is a photographic film used to measure radioation
* Photographic film turns dark when it absorbs radiatoin
* This si useful for people who work on radiation as the more radiation they are exposed to the darker the film becomes
* Workers can know when they have been exposed to too much radiation
