Particles Flashcards
What are atoms made up of?
Protons, Neutrons and Electrons
What is there inside every atom?
A nucleus
What does the nucleus contain?
Protons and Neutrons
What are protons and neutrons both known as?
Nucleons
What are nucleons?
Protons and neutrons are both known as nucleons
What orbits the nucleus of an atom?
Electrons
Why do we generally use the relative charge and mass of subatomic particles?
Because their charges and masses are so tiny that its often easier to talk about their relative charges and masses
What is the relative charge of a proton?
+1
What is the relative charge of a neutron?
0
What is the relative charge of an electron?
-1
What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
0.0005
What is the proton number?
The proton number is the number of protons in the nucleus
What is the proton number sometimes called and what is its symbol?
The proton number is sometimes called the atomic number and has the symbol Z.
Z is just the number of protons in the nucleus
What is the relationship between the proton number and the definition of an element?
Its the proton number that defines an element, no two elements will have the same number of protons
In a neutral atom what is the relationship between the number of electrons and protons?
In a neutral atom the number of electrons equals the number of protons.
What does an element’s reactions and chemical behaviour depend on?
The number of electrons
What is an ion?
An ion is a particle with a different number of electrons to protons
What is the nucleon number?
The nucleon number is the total number of protons and neutrons
What is the nucleon number also called and what symbol does it have?
The nucleon number is also called the mass number and has the symbol A
What is the number of nucleons in an atom the same as and why?
Since each proton or neutron has a relative mass of 1 and the electrons weigh virtually nothing the number of nucleons is the same as the atom’s relative mass
What does the nuclide notation of an element do?
Summarise information about its atomic structure
Is the nucleon number the top or bottom number on an elements nuclide notation?
Top
Is the proton number the top or bottom number on an elements nuclide notation?
Bottom
What are isotopes?
Isotopes are atoms with the same number of protons but different numbers of neutrons
What are isotopes in terms of nuclide notation?
Isotopes have the same proton number but different nucleon numbers
What is the relationship between changing the number of neutrons and an atom’s chemical properties?
Changing the number of neutrons doesn’t affect the atoms chemical properties
What does the number of neutrons affect?
The stability of the nucleus
What does the stability of the nucleus depend on?
The number of neutrons
What may unstable nuclei be and what may they do over time?
Unstable nuclei may be radioactive and decay over time into different nuclei that are more stable
What can radioactive isotopes be used for?
To find out how old things are
How can radioactive isotopes be used to find out how old things are?
1- All living things contain the same percentage of radioactive carbon-14 taken in from the atmosphere
2- After they die the amount of carbon-14 inside them decreases over time as it decays to stable elements
3- Scientists can calculate the approximate age of archaeological finds made from dead organic matter by using isotopic data (amount of each isotope present) to find the percentage of radioactive carbon-14 that’s left in the object
What is the specific charge of a particle?
The specific charge of a particle is the ratio of its charge to its mass
What are the units of specific charge?
Coulombs per kilogram (C/Kg)
What is the formula used to calculate specific charge?
Specific charge = Charge / Mass
What is a fundamental particle?
A fundamental particle is one that you can’t break up into anything smaller
When calculating the specific charge of an ion that has lost an electron what do you need to consider?
The overall charge of the ion which is done by deducing how many protons and electrons there are now present in the ion
What binds nucleons together?
The strong nuclear force
What are the two forces acting on the protons and neutrons in a nucleus?
- Electrostatic forces from the proton’s electric charges
- Gravitational forces due to the masses of the particles
What is the strong nuclear force?
The strong nuclear force is an attractive force that holds the protons and neutrons in the nucleus together therefore holding the nucleus together
Explain why the strong nuclear force exists
The repulsion from the electrostatic force is much bigger than the gravitational attraction between nucleons. If these were the only forces acting in the nucleus the nucleons would fly apart so there must be another attractive force that holds the nucleus together called the strong nuclear force
In order to hold the nucleus together what must the strong nuclear force be in relation to the electrostatic force?
To hold the nucleus together it must be an attractive force that’s stronger than the electrostatic force
What is the general size of the range of the strong nuclear force?
Experiments have shown that the strong nuclear force has a very short range. It can only hold nucleons together when they are separated by up to a few femtometres - the size of a nucleus
What is the relationship between the strength of the strong nuclear force and its range?
The strength of the strong nuclear force quickly falls beyond its range (a few femtometers)
What is the relationship between the strong nuclear force and all nucelons?
Experiments show that the strong nuclear force works equally between all nucleons. This means that the size of the force is the same whether its proton-proton, neutron-neutron or proton-neutron
What can be said about the strong nuclear force at very small separations of nucleons?
At very small separations of nucleons the strong nuclear force must be repulsive or it would crush the nucleus to a point
What does the size of the strong nuclear force depend on?
Nucleon separation
At what distance of nucleon separation is the strong nuclear force repulsive?
Less than 0.5 femtometres
As nucleon separation increases past 0.5fm what happens to the strong nuclear force?
The strong nuclear force becomes attractive. It reaches a maximum attractive value and then falls rapidly towards zero after 3fm
At what distance of nucleon separation is the strong nuclear force attractive?
Between 0.5fm and 3fm
What is the general size of the range of the electrostatic repulsive force?
The electrostatic repulsive force extends over a much larger range than the strong nuclear force (indefinitely)
Where does alpha emission happen?
Alpha emission only happens in very big nuclei like uranium and radium
Why does alpha emission happen in very big nuclei?
Alpha emission only happens in very big nuclei as the nuclei of these atoms are just too massive for the strong nuclear force to keep them stable
What is the effect on the nuclide notation of an element when an alpha particle is released?
The proton number decreases by two and the nucleon number decreases by four
What is the range of alpha particles and how can this be observed?
- Alpha particles have a very short range, only a few cm in air.
- This can be seen by observing the tracks left by alpha particles in a cloud chamber. You could also use a Geiger counter ( a device that measures the amount of ionising radiation). Bring it up close to the alpha source, then move it away slowly and observe how the count rate drops
Where does beta minus decay happen?
Beta minus decay happens in neutron rich nuclei which are isotopes that are unstable due to having too many more neutrons than protons in their nucleus
What is beta minus decay?
Beta minus decay is the emission of an electron from the nucleus along with an antineutrino
What happens when a nucleus ejects a beta particle?
When a nucleus ejects a beta particle one of the neutrons in the nucleus is changed into a proton
What is the effect on the nuclide notation of an element when a beta particle is ejected from a nucleus?
The proton number increases by one and the nucleon number stays the same
What is the relationship between the range of an alpha particle and a beta particle?
Beta particles have a much greater range than alpha particles
In beta decay as well as a beta particle what do you also get?
In beta decay as well as a beta particle you also get a tiny neutral particle called an antineutrino released. This antineutrino carries away some energy and momentum
Why were neutrinos first hypothesised?
Neutrinos were first hypothesised due to observations of beta decay
Explain how observations of beta decay led to the hypothesis of the neutrino
1- Scientists originally thought that the only particle emitted from the nucleus during beta decay was an electron.
2- However, observations showed that the energy of the particles after the beta decay was less than it was before which didn’t fit with the principle of conservation of energy
3- In 1930 Wolfgang Pauli suggested another particle was being emitted too and it carried away the missing energy. This particle had to be neutral or charge wouldn’t be conserved in beta decay and had to have zero or almost zero mass as it had never been detected
4- Other discoveries led to Pauli’s theory becoming accepted and the particle was named the neutrino
What are photons?
Photons are packets of electromagnetic radiation
What is the electromagnetic spectrum?
The electromagnetic spectrum is a continuous spectrum of all the possible frequencies of electromagnetic radiation
What is the electromagnetic spectrum in order of frequency from lowest to highest and wavelength from highest to lowest?
1- Radio waves
2- Micro waves
3- Infra red
4- Visible light
5- Ultraviolet
6- X-rays
7- Gamma rays
What equation links frequency and wavelength?
- f=c/λ
c = 3.00*10^8
What does electromagnetic radiation exist as?
Electromagnetic radiation exists as photons of energy
What does the energy of a photon depend on?
The energy of a photon depends on the frequency of the radiation
What is the formula used to calculate the energy of a photon?
E=hf=hc/λ
What does every particle have?
Every particle has an antiparticle
What are the properties of a particle’s antiparticle?
Each particle has a matching antiparticle with the same mass and rest energy but with opposite charge
What is the antiparticle of a proton
An antiproton
What is the antiparticle of a neutron?
An antineutron
What is the antiparticle of an electron?
A positron
What is the antiparticle of a neutrino?
An antineutrino
How do you convert MeV to joules?
- Multiply by 10^6 to get eV
- Multiply by 1.6*10^-19 to get Joules
What is the relationship between matter and antimatter and energy?
You can create matter and antimatter from energy
What is the rest energy of a particle?
The rest energy of a particle is just the energy equivalent of the particle’s mass measured in MeV
What happens when energy is converted into mass?
When energy is converted into mass you get equal amounts of matter and antimatter
What happens when you fire two protons at each other at high speed?
When you fire two protons at each other at high speed you end up with a lot of energy at the point of impact. This energy might be converted into more particles. If an extra proton is formed then there will always be an antiproton to go with it. This is called pair production
At less than ____ the strong nuclear force is ______
0.5 fm
repulsive
Between ____ and ____ the strong nuclear force is _______
0.5 fm
3.0 fm
attractive
Beyond ____ the strong nuclear force is ____
3.0 fm
zero
Describe pair production by a photon
1) a photon collides with a nucleus (the nucleus so that momentum is conserved)
2) if the photon has sufficient energy, a particle and an antiparticle are formed
What is each particle-antiparticle pair produced from
A single photon
What form is energy that gets converted into matter and antimatter in?
Energy that gets converted into matter and antimatter is in the form of a photon
When only does pair production happen?
Pair production only happens if one photon has enough energy to produce that much mass - only gamma ray photons have enough energy
Why does pair production tend to happen near a nucleus?
Pair production tends to happen near a nucleus which helps to conserve momentum
Which particle-antiparticle pair is usually produced during pair production and why?
You usually get electron-positron pairs produced rather than any other pair because they have a relatively low mass
What is the minimum energy for a photon to undergo pair production?
The minimum energy for a photon to undergo pair production is the total rest energy of the particles produced
What is the equation for the minimum energy of a photon in pair production?
- Emin = hf min = 2Eo
- Eo is the rest energy of each particle produced
What do the particle and antiparticle have a rest energy of in pair production?
2Eo
During pair production why is a particle and an antiparticle produced?
A particle and an antiparticle is produced to conserve charge as photons do not have any charge
What is the minimum amount of energy needed for a photon to undergo pair production equal to?
The total rest energy of the particles produced
What is the relationship between the rest energy and kinetic energy of particles before and after pair production?
Rest energy + Kinetic energy of particles before pair production = Rest energy + Kinetic energy of all particles after
Draw a diagram to show the pair production of an electron and a positron
See page 7 in revision guide
Why are the tracks of the particles produced during pair production usually curved?
The particle tracks are curved because there’s usually a magnetic field present in particle physics experiments. They curve in opposite directions because of the opposite charges on the electron and positron
Define annihilation
The process by which a particle and its antiparticle meet and their mass gets converted into energy in the form of a pair of photons
What is the opposite of pair production?
Annihilation
When does annihilation occur?
Annihilation occurs when a particle meets its antiparticle
What equation shows the energy in annihilation?
2Eo (+ KE) = 2hf
- Eo is the rest energy of the particles
Draw a diagram to show the annihilation of an electron and a positron
See page 7 in the revision guide
Why are two photons produced in annihilation?
To conserve momentum
What are forces caused by?
Particle exchange
What are gauge bosons?
Gauge bosons are exchange particles
What is the repulsion between two protons caused by?
The repulsion between two protons is caused by the exchange of virtual photons which are the gauge bosons of the electromagnetic force.
What are gauge bosons and what does this mean?
Gauge bosons are virtual particles which means they only exist for a very short time
How many fundamental forces are there?
Four
What are the four fundamental forces?
- The Strong Nuclear force
- The Weak Nuclear force
- The Electromagnetic force
- Gravity
What is the gauge boson for the electromagnetic force?
The virtual photon (γ)
What is the gauge boson for the weak nuclear force?
W⁺ and W⁻ bosons
What is the gauge boson for the strong nuclear force?
The gauge bosons for the strong nuclear force are pions between nucleons (π+, π0, π–) and gluons between quarks
Which particles does the electromagnetic force affect?
The electromagnetic force affects charged particles only
Which particles does the weak nuclear force affect?
The weak nuclear force affects all types of particles
Which particles does the strong nuclear force affect?
The strong nuclear force affects hadrons only
In the strong nuclear force what are pions described as being exchanged between?
In the strong nuclear force pions are described as being exchanged between nucleons
Why do particles physicists never bother about gravity?
Particle physicists never bother about gravity because it is so incredibly feeble compared with the other types of interaction therefore gravity only really matters when you have got really big masses like stars and planets
What is the relationship between the mass of a gauge boson and the range of the force?
The larger the mass of the gauge boson the shorter the range of the force
What effect does the mass of a W boson have on the range of the weak nuclear force?
The W bosons have a mass of about 100 times that of a proton which gives the weak force a very short range. Creating a virtual W particle uses so much energy that it can only exist for a very short time and it can’t travel far
What effect does the mass of a photon have on the range of a force?
A photon has zero mass which gives you a force with infinite range
On a Feynman diagram how are gauge bosons represented?
Gauge bosons are represented by wiggly lines
On a Feynman diagram how are particles other than gauge bosons represented?
Particles other than gauge bosons are represented by straight lines
Draw the Feynman diagram to show electromagnetic repulsion between two electrons
See page 9 in the revision guide
Draw the Feynman diagram to show the electromagnetic repulsion between two positrons
See page 9 in the revision guide
Draw the Feynman diagram to show electron capture and state the symbol equation for this interaction
- p + e —> n + Ve
See page 9 in the revision guide
Draw the Feynman diagram to show an electron proton collision and state the symbol equation for this interaction
- p + e —> n + Ve
See page 17 in the particles notes pack
Draw the Feynman diagram to show Beta-Minus decay and state the symbol equation for this interaction
- n —> p + e- + ̅νe
See page 9 in the revision guide
Draw the Feynman diagram to show Beta-Plus decay and state the symbol equation for this interaction
- p —> n + e+ + Ve
See page 9 in the revision guide
What type of neutrino do you get in Beta plus and minus decay and why?
You get an antineutrino in Beta minus decay and a neutrino in Beta plus decay so that lepton number is conserved
What are hadrons?
Hadrons are particles that feel the strong nuclear force such as protons and neutrons
Are hadrons fundamental particles?
Hadrons are not fundamental particles as they are made up of smaller particles called quarks
How many different types of hadrons are there?
Two
What are the two different types of hadrons and how are they classified?
The two different types of hadrons are baryons and mesons. They are classified according to the number of quarks that make them up
Are protons and neutrons baryons?
Yes
What is the relationship between protons and neutrons and baryons?
Protons and neutrons are baryons
What is the relationship between protons and baryons?
The proton is the only stable baryon
What is the relationship between all baryons except protons and stability?
All baryons except protons are unstable. This means that they decay to become other particles. The particles a baryon ends up as depends on what it started as but it always includes a proton
Why are protons the only stable baryon?
As they don’t decay
What do all baryons except protons decay to?
All baryons except protons decay to a proton
What is the relationship between the antiparticles of protons and neutrons and baryons?
The antiparticles of protons and neutrons - antiprotons and antineutrons are antibaryons
Why do you not find antibaryons in ordinary matter?
Antiparticles are annihilated when they meet the corresponding particle which means that you don’t find antibaryons in ordinary matter
Define the term Baryon number
The Baryon number is the number of baryons in an interaction
What is the baryon number of protons and neutrons?
+1
What is the baryon number of antibaryons?
-1
What is the baryon number of particles that are not baryons?
0
What must baryon number always be during interactions?
Baryon number is a quantum number that must be conserved in any interaction. This means that when an interaction happens the baryon number on either side of the interaction must be the same
What can be said about the total baryon number in particle interactions?
The total baryon number in any particle interaction never changes
What are the 4 main rules for drawing Feynman diagrams?
1- Incoming particles start at the bottom of the diagram and move upwards
2- The baryons and leptons can’t cross from one side to the other
3- Make sure the charges on both sides balance. (The W bosons carry charge from one side of the diagram to the other)
4- A W- particle going to the left has the same effect as a W+ particle going to the right
What are neutrons?
Neutrons are baryons that decay into protons
When a neutron decays what does it form?
When a neutron decays it forms a proton, an electron and an antineutrino
What is the symbol equation for when a neutron decays?
n —> p + e- + ̅νe
What is the relationship between baryon number and the decay of a neutron?
Electrons and antineutrinos are not baryons so they have a baryon number of 0 Neutrons and protons have a baryon number of 1 so the baryon numbers on both sides are equal so the interaction can happen
What are the two main types of mesons?
Pions and Kaons
What is the relationship between all mesons and stability?
All mesons are unstable
What is the baryon number of mesons?
0 as they are not baryons
Are pions the lightest or heavier mesons?
Pions are the lightest mesons
What are the three different versions of pions?
You get three different versions of pions with different electric charges (π+, π0, π −)
Are kaons the lightest or heavier mesons and are they more or less stable than pions?
Kaons are heavier and more unstable than pions
Where were pions and kaons discovered?
Pions and Kaons were discovered in cosmic rays - cosmic ray showers are a source of both particles. You can observe the tracks of these particles with a cloud chamber
How do mesons interact with baryons?
Mesons interact with baryons via the strong nuclear force
Draw a diagram showing the summary of hadron properties
See page 11 in the revision guide
What is the relationship between leptons such as electrons and neutrinos and the strong nuclear force?
Leptons don’t feel the strong nuclear force
What are leptons?
Leptons are fundamental particles and they don’t feel the strong nuclear force. They only really interact with other particles via the weak interaction (along with a bit of gravitational force and the electromagnetic force as well if they are charged.)
What is the relationship between electrons and stability?
Electrons are stable
What are muons?
Muons are like heavy electrons
What is the relationship between muons and stability?
Muons are unstable and decay eventually into ordinary electrons
What is the relationship between electron and muon leptons and neutrinos?
The electron and muon leptons each come with their own neutrino, νe and νμ
Explain what a neutrino is in terms of its mass and charge?
Neutrinos have zero or almost zero mass and zero electric charge so they don’t do much. Neutrinos only take part in weak interactions.
What is the general rule that has to be followed when counting the types of lepton?
You have to count the electron lepton number and muon lepton number separately
What is the lepton number?
The lepton number is just the number of leptons
What are the two different types of lepton number?
- Electron lepton number (Le)
- Muon lepton number (Lμ)
What is the lepton number of a lepton?
+1
What is the relationship between leptons and lepton neutrinos and their antiparticles in terms of charge and lepton number?
- The antiparticles have the opposite charge and lepton numbers to their matching particles
What is the relationship between quarks and fundamental particles?
Quarks are fundamental particles
What are quarks?
Quarks are the building blocks for hadrons (baryons and mesons). Antiparticles of hadrons are made from antiquarks
How many types of quarks do you need to make protons and neutrons and what type of quarks are needed?
To make protons and neutrons you only need two types of quarks - the up quark (u) and the down quark (d)
What quark is needed to make particles with the property strangeness?
The strange quark (s)
Is strangeness a quantum number and what does this mean?
Strangeness is a quantum number which means it can only take a certain set of values
How are strange particles created?
Strange particles are created via the strong interaction but decay via the weak interaction
When is strangeness conserved?
Strangeness is conserved in the strong interaction but not in the weak interaction
Are strange particles produced on their own or in pairs?
Strange particles are always produced as pairs
Why are strange particles always produced in pairs?
When strange particles are produced in pairs one has a strangeness of +1 and the other has a strangeness of -1 so the overall strangeness of 0 is conserved
What is the relationship between quarks and antiquarks in terms of their properties?
Quarks and antiquarks have opposite properties
How many quarks are baryons made from?
Baryons are made from three quarks
Where did evidence for quarks come from?
Evidence for quarks came from hitting protons with high energy electrons. The way the electrons scattered showed that there were three concentrations of charge (quarks) inside the proton
How many quarks are mesons made from?
Mesons are made from two quarks
Which quarks are mesons made from?
Mesons are made from a quark and an antiquark
What is the antiparticle of a π0 meson?
The antiparticle of a π0 meson is itself
What combination of quarks are pions made from?
Pions are just made from combinations of up, down, anti-up and anti-down quarks
What is the relationship between Kaons and strange quarks?
Kaons have strangeness so you need to put in s quarks as well remembering an s quark has a strangeness of -1
When only can the quark type be changed?
The quark type can only be changed during the weak interaction
During beta minus decay which quark is changed and why?
In Beta minus decay a neutron is changed into a proton. This means turning a d quark into a u quark which only the weak interaction can do
During beta plus decay which quark is changed and why?
In beta plus decay a proton changes to a neutron so a u quark changes to a d quark.
Which 6 properties are conserved in particle interactions?
- Charge
- Baryon number
- Strangeness in strong interactions
- Lepton number
- Energy
- Momentum
What are the 4 main properties that are conserved in particle interactions?
- Charge
- Baryon number
- Strangeness in strong interactions
- Lepton number
Explain how charge is conserved during particle interactions
Charge is always conserved meaning the total charge after an interaction must be equal to the total charge before the interaction
Explain how baryon number is conserved during particle interactions?
Baryon number is always conserved. The baryon number after an interaction must equal the baryon number before the interaction
Explain how strangeness is conserved during particle interactions
Strangeness is only conserved in strong interactions. The only way to change the type of quark is with the weak interaction so in strong interactions there has to be the same number of strange quarks at the beginning as at the end
Explain how lepton number is conserved during particle interactions
The different types of lepton number (electron and muon) have to be conserved separately.
Is there such a things as a free quark and is it possible to separate out quarks by blasting a proton with enough energy at them?
There is no such thing as a free quark. If you blasted a proton with enough energy the quarks would not be separated, instead the energy just gets changed into more quarks and antiquarks so it is just pair production again and you make mesons. It is not possible to get a quark by itself, this is called quark confinement
How is modern knowledge and understanding about particle physics changing?
- New theories are created to try to explain observations from experiments. Sometimes physicists hypothesise a new particle and the properties they expect it to have
- Experiments to try to find the existence of this new particle are then carried out. Results from different experiments are combined to try to confirm the new particle. If it exists, the theory is more likely to be correct and the scientific community start to accept it, its validated.
- Experiments in particle physics often need particles travelling at incredibly high speeds. This can only be achieved using particle accelerators. These huge pieces of equipment are very expensive to build and run. This means that large groups of scientists and engineers all over the world have to collaborate to be able to fund these experiments
