Section 1 - Particles Flashcards
1
Q
Describe the nuclear model of an atom.
A
- Central nucleus containing protons and neutrons
* Electrons orbit the nucleus
2
Q
What are nucleons?
A
Protons and neutrons
3
Q
What is the collective name for protons and neutrons?
A
Nucleons
4
Q
How the charge and mass of protons, neutrons and electrons usually given?
A
- It can be given and coulombs and kilograms, but the numbers are very small (e.g. +1.60 x 10^-19 coulombs)
- Therefore, the RELATIVE charges and masses are used instead sometimes (e.g. +1)
5
Q
Do you need to learn the charges and masses of protons, electrons and neutrons?
A
No, they are given to you in the exam. However, you need to know the RELATIVE charges and masses.
6
Q
What is the unit for charge of particles?
A
Coulombs (C)
7
Q
What is the unit for the mass of a particle?
A
Kilograms (kg)
8
Q
What is the charge of protons, neutrons and electrons?
A
- Protons = + 1.60 x 10^-19 C
- Neutrons = 0 C
- Electrons = - 1.60 x 10^-19 C
9
Q
What is the mass of protons, neutrons and electrons?
A
- Protons = 1.67 x 10^-27 kg
- Neutrons = 1.67 x 10^-27 kg
- Electrons = 9.11 x 10^-31 kg
10
Q
What is the relative charge of protons, neutrons and electrons?
A
- Protons = +1
- Neutrons = 0
- Electrons = -1
11
Q
What is the relative mass of protons, neutrons and electrons?
A
- Protons = 1
- Neutrons = 1
- Electrons = 0.0005
12
Q
What is the symbol for proton number?
A
Z
13
Q
What is the symbol Z?
A
The proton number
14
Q
What does the proton number determine?
A
Which element the atom is of.
15
Q
What does the electron number determine?
A
The chemical behaviour and reactions.
16
Q
What is another name for the mass number?
A
The nucleon number.
17
Q
What is the nucleon number?
A
The number of protons and neutrons.
18
Q
What is the symbol for nucleon number?
A
A
19
Q
What is the symbol A?
A
The nucleon number.
20
Q
What is an atom’s relative atomic mass equal to?
A
The nucleon number (the number of protons and neutrons).
21
Q
What are isotopes?
A
Atoms with the same number of protons but different number of neutrons.
22
Q
What are the 3 isotopes of hydrogen and what is their composition?
A
- Hydrogen - 1 proton, 0 neutrons
- Deuterium - 1 proton, 1 neutron
- Tritium - 1 proton, 2 neutrons
23
Q
How does changing the number of neutrons in atom affect it?
A
- Doesn’t affect the chemical properties
* Affects the stability of the nucleus -> May cause decay
24
Q
How can isotopes be used to find out how old a sample is?
A
The amount of radioactive carbon-14 left in a sample can be used to calculate the approximate age (if the object is made of organic matter).
25
Why can carbon-14 be used to find out how old stuff is?
* All living things contain the same percentage of carbon-14 taken in from the atmosphere
* After they die, the amount of carbon-14 decreases with time as it decays
* Looking at a sample, the amount of carbon-14 tells you how old it is
26
What is specific charge?
The ratio of the charge of a particle to its mass.
27
What is the unit for specific charge?
Coulombs per kilogram (C/kg)
28
What is the equation for specific charge?
Specific charge = Charge / Mass
29
What would happen in the nucleus if the strong attraction didn't exist?
Electrostatic repulsion would overcome gravity and the particles would fly apart.
30
What does the strong nuclear force do?
Binds nucleons together in the nucleus.
31
What are the properties of the strong nuclear force?
* Stronger than the electrostatic force
* Very short range - only a few femtometres (the size of a nucleus)
* Works equally between all nucleons (i.e. The force is the same between proton-proton, neutron-neutron, neutron-proton)
* At very short separations, it is repulsive. At larger separations, it is attractive.
32
Describe how the strong nuclear force changes with separation.
* At very small separations (below 0.5fm), it is repulsive
* At the "equilibrium distance" (about 0.5fm), no force is exerted
* At larger separations (over 0.5fm), it is attractive. It reaches a maximum attractive value and then falls rapidly. It is almost zero past 3fm.
33
Why must the strong nuclear force be repulsive at very small separations?
Otherwise it would crush the nucleus to a point.
34
In what nuclei does alpha emission happen and why?
* Very big nuclei, like uranium and radium.
| * The nuclei are too massive for the strong nuclear force to keep them stable.
35
What happens to proton number and nucleon number when alpha decay happens?
* Proton number decreases by 2
| * Nucleon number decreases by 4
36
Compare when alpha and beta emission happen.
* Alpha emission -> In very large nuclei
| * Beta emission -> In neutron-rich nuclei
37
What is the range of alpha particles and how can this be observed?
* Very short
* By looking at tracks left by alpha particles in a cloud chamber or by using a Geiger counter to observe how count rate drops with distance
38
What is beta-minus decay?
The changing of a neutron into a proton, while emitting an electron and antineutrino from the nucleus.
39
In what nuclei does beta-minus decay happen and why?
* Neutron-rich nuclei
| * Having many more neutrons than protons in the nucleus makes it unstable
40
What happens to proton number and nucleon number when beta-minus decay happens?
* Proton number increases by 1
| * Nucleon number stays the same
41
What is the range of beta particles?
Much greater than alpha particles.
42
What does the antineutrino in beta decay do?
Carries away some energy and momentum.
43
Describe how the first hypothesis about neutrinos was created.
* Scientists at first thought only electrons were emitted during beta decay.
* However, it was observed that the energy after beta decay was less than before beta decay.
* This led to the idea that another particle was emitted too, which carried the missing energy.
* It would have to have no charge and almost zero mass.
* This was later found to be the neutrino.
44
Remember to revise the graph of the strong nuclear force.
Pg 4 of the revision guide.
45
What is the order of the EM spectrum by increasing frequency?
* Radio waves
* Microwaves
* Infrared
* Visible light
* UV
* X-rays
* Gamma rays
46
What equation links frequency and wavelength of EM waves?
Frequency = Speed of Light in Vacuum / Wavelength
f = c / lambda
(NOTE: This is a variation of the "v = f x lambda" equation)
47
What is the speed of light in a vacuum?
3.00 x 10^8 m/s
48
What are photons?
Packets of electromagnetic radiation.
49
When are EM waves emitted?
When a charged particle loses energy. This can be when:
• A fast-moving electron is stopped
• An electron in a shell moves to a shell of lower energy
50
Describe the structure of an EM wave.
A magnetic wave and an electric wave at 90* to each other and to the direction of travel. They are in phase.
(See diagram pg 8 of textbook)
51
What is the equation for the energy of a photon?
Energy (J) = Planck's constant (Js) x Frequency (Hz)
E = h x f
52
What is the wavelength of visible light?
400-700nm
53
What is Planck's constant?
6.63 x 10^-34 Js
54
What is the equation for the power of a laser?
Power = No. of photons passing a point per second x Photon energy
P = n x E = n x h x f
55
What units may be used to give the energy of a photon?
Joules (J) or Mega electronvolts (MeV)
56
How many joules is one MeV?
1.60 x 10^-13 J
57
What equation can be used to calculate the rest energy of a particle?
E = m x c^2
58
What is an electronvolt?
The energy that one electron would gain when accelerated through a potential difference of 1 volt.
59
How do you convert from joules to MeV?
Divide by 1.6 x 10^-13.
60
What is an antiparticle?
A corresponding particle to a particle with the same mass and rest energy, but opposite charge.
61
What is the general unit for rest energy?
MeV
62
Describe simply the idea of energy and mass equivalence.
Energy can turn into mass and mass can turn into energy.
63
What is the rest energy of a particle?
The "energy equivalent" of the particle's mass.
64
What happens in terms of mass production when energy is converted into mass?
Equal amounts of matter and antimatter are produced.
65
What is the antiparticle of the proton?
Antiproton
66
What is the antiparticle of the neutron?
Antineutron
67
What is the antiparticle of the electron?
Positron
68
What is the antiparticle of the neutrino?
Antineutrino
69
What is beta-plus decay?
* When a proton turns into a neutron, and a positron and neutrino are emitted.
* It is not a natural form of decay and it only happens in experiments.
70
What is pair production?
When a photon turns into a particle and antiparticle.
71
When can pair production happen?
When the photon has enough energy to produce the mass of the particle and antiparticle.
72
Which photons have enough energy to produce mass through pair production?
Gamma ray photons.
73
Where does pair production usually happen and why?
Near the nucleus, which helps conserve momentum.
74
What are the most common particles produced by pair production and why?
Electron-positron pairs because they have low mass.
75
The minimum energy of a photon in pair production is equal to...
...the total rest energy of the particles produced.
76
What is the symbol for rest energy?
E0
77
What is the equation for the minimum energy of a photon during pair production?
Minimum energy of photon = 2 x Rest energy of each particle produced
Emin = 2E0
or
h x fmin = 2E0
78
What happens when a particle and antiparticle meet?
* Annihilation
| * All of the mass of the particles is converted back to energy.
79
The total minimum energy of both photons produced in annihilation is equal to...
... the total of the minimum energies of the particle and antiparticle.
80
What is the energy for the minimum energy of a photon produced in annihilation?
Total minimum energy of both photons = Total minimum energy of particle and antiparticle
2Emin = 2E0 ...and so... Emin = E0
81
Is the interaction between two distant objects instantaneous?
No - this is explained by the need for exchange particles, which cause forces.
82
What is the collective name for exchange particles?
Gauge bosons
83
What are the four fundamental forces?
* Weak nuclear force
* Strong nuclear force
* Electromagnetic force
* Gravity
84
What is the exchange particle of electromagnetic force?
Virtual photon (gamma symbol)
85
What particles are affected by the electromagnetic force?
Charged particles
86
What is the exchange particle of the weak nuclear force?
W+, W- and Z0 bosons
87
What particles are affected by the weak nuclear force?
All types
88
What is the exchange particle of the strong nuclear force?
* Gluons exchanged between quarks
| * Pions exchanged between nucleons
89
What particles are affected by the strong nuclear force?
Hadrons only
90
What is the exchange particle of gravity?
Graviton
91
What particles are affected by gravity?
All types
92
Is particle physics concerned with gravity?
Not really - it is usually ignored because it is very feeble unless large masses are involved.
93
What is the mass of a W boson?
About 100 times that of a proton.
94
Compare and explain the ranges of a W boson and a photon.
* W boson - Very short range because it has a large mass. This means it requires a lot of energy to create and can't travel very far.
* Photon - Infinite range because it has zero mass.
95
What are the different types of line on a Feynman diagram used to represent?
* Gauge bosons (exchange particles) - wiggly lines
| * Other particles - straight lines
96
What are the rules for drawing Feynman diagrams?
* Incoming particles start at the bottom and move upwards
* Baryons and leptons can't cross from one side to the other
* Make sure charges on both sides balance
* A W- particle going to the left has the same effect as a W+ parcial going to the right
97
What exchange particle is involved in two electrons repelling each other?
Virtual (gamma) photon
98
What are electron capture and electron-proton collisions?
* Electron capture is when a proton and electron are attracted by the electromagnetic interaction and a W+ boson goes from the proton to the electron, causing a neutron and neutrino to be formed.
* Electron collision is when the proton and electron collide. The same products are formed but a W- boson travels from the electron to the proton instead.
99
What is the difference between electron capture and electron-proton collision?
* In electron capture, a W+ boson travels from the proton to the electron.
* In electron-proton collisions, a W- travels from the electron to the proton.
100
What is the particle equation for beta-minus decay?
Neutron -> Proton + Electron + Antineutrino
101
What is the particle equation for beta-plus decay?
Proton -> Neutron + Positron + Neutrino
102
Why is an antineutrino produced in beta-minus decay, while a neutrino is produced in beta-plus decay?
To conserve lepton number.
103
What is a virtual particle?
Particles which exist for only a very short time and cannot be detected.
104
Remember to learn specific Feynman diagrams.
Pg 9
105
Practice drawing our a spider diagram of the different types of particles.
Do it!
106
What are hadrons?
Particles that feel the strong nuclear force. They are not fundamental.
107
What are hadrons made of?
Quarks
108
Are hadrons fundamental particles?
No, they are made of quarks.
109
What are the two types of hadrons?
* Baryons
| * Mesons
110
What is the difference between baryons and mesons?
* Baryons - Made of 3 quarks and decay into a proton directly or indirectly
* Mesons - Made of a quark and antiquark and do not decay into a proton
111
Name some baryons.
* Protons
* Neutrons
* Other particles (e.g. Sigmas)
112
What is the only stable baryon?
Proton - this means all baryons will decay in sequence and eventually form a proton.
113
Are antibaryons found in ordinary matter?
No, because they annihilate with baryons.
114
What values are particles given in baryon number conservation?
* Baryons = +1
* Antibaryons = -1
* Other particles = 0
115
What are some examples of antibaryons?
* Antiprotons
| * Antineutrons
116
Why does beta decay happen?
Neutrons are not stable baryons, but protons are, so a neutron will decay into a proton.
117
Are mesons stable?
No
118
What are the different types of meson?
Pions and kaons
119
What is another name for a pion?
Pi-meson
120
What is another name for a kaon?
K-meson
121
What is the difference between pions and kaons?
* Pions - Lighter, less unstable, not strange
| * Kaons - Heavier, more unstable, strange
122
What happens to kaons?
They decay into pions.
123
How were pions and kaons discovered?
In cosmic rays.
124
How do mesons interact with baryons?
Through the strong force.
125
What are the general rules for determining the type of interaction in a reaction?
* If any leptons involved at all -> Weak interaction
* If strangeness isn't conserved -> Weak interaction
* All others -> Strong interaction
126
What are leptons?
Particles that do not feel the strong interaction. They are fundamental.
127
What are the different leptons?
* Electrons
* Muons
* Neutrinos
* Tau
128
What happens to muons?
The eventually decay into electrons. This is because muons are unstable.
129
What can muons be described as?
Heavy electrons.
130
What is the mass and charge of neutrinos?
* Mass - Almost zero
| * Charge - Zero
131
How does lepton conservation work?
* There are 3 generations of lepton number - electron, muon and tau
* Each lepton number must be conserved separately
* Each normal lepton and its respective neutrino is given a lepton number of +1
* Each anti-lepton and its respective antineutrino is given a lepton number of -1
132
What are the symbols for each lepton number?
* Electron lepton number = Le
* Muon lepton number = Lmuon
* Tau lepton number = Lt
133
What are antiparticles of hadrons made from?
Antiquarks
134
How do strange particles (e.g. kaons) interact?
* Created by the strong interaction
| * Decay via the weak interaction
135
Strange particles are always produced in pairs (e.g. K+ and K-). Why?
The strangeness cancels out to become 0, so that strangeness is conserved. Therefore, the reaction is a strong interaction.
136
What are the types of quark?
* Up
* Down
* Strange
137
What is the charge of an up quark?
+2/3
138
What is the charge of a down quark?
-1/3
139
What is the charge of a strange quark?
-1/3
140
What is the charge of an anti-up antiquark?
-2/3
141
What is the charge of an anti-down antiquark?
+1/3
142
What is the charge of an anti-strange antiquark?
+1/3
143
What is the strangeness of a strange quark?
-1
144
What is the strangeness of an anti-strange antiquark?
+1
145
What is unusual about strangeness?
* It is not ALWAYS conserved
| * Strange quarks are given a strangeness of -1 and anti-strange antiquarks are given a strangeness of +1
146
What quarks make up a proton?
uud
147
What quarks make up an antiproton?
anti-u, anti-u, anti-d
148
What quarks make up a neutron?
udd
149
What quarks make up an antineutron?
anti-u, anti-d, anti-d
150
What are baryons made of?
3 quarks
151
What are mesons made of?
A quark and an antiquark
152
What is the antiparticle of a pi-plus meson?
A pi-minus meson.
153
Remember to revise the diagram on mesons.
Pg 14 of the revision guide
154
What is a weak interaction in terms of quarks?
A weak interaction is something that changes the quark type (e.g. A neutron (udd) turning into a proton (uud))
155
What properties are conserved in an interaction?
* Charge
* Baryon number
* Strangeness (only in strong interactions)
* Lepton number (all 3 generations separately)
156
Can a quark exist on its own?
No.
157
What is quark confinement?
The idea that quarks cannot exist not their own.
158
Through which interaction do hadrons tend to decay?
Weak
159
Describe the mass, range and charge of a W boson.
* Non-zero rest mass
* 0.001fm range
* Can be positively or negatively charged
160
What are the quarks in a K0 meson?
* Anti-s
| * d
161
What are the quarks in an anti-K0 meson?
* s
| * Anti-d
