Particle Physics Flashcards
To revise particle physics
Describe the nuclear model of the atom
A positive nucleus containing protons and neutrons with electrons found in shells orbiting the nucleus
State the relative charge of all sub atomic particles
Proton +1
Neutron 0
Electron -1
State the relative masses of all sub atomic particles
Proton 1
Neutron 1
Electron almost 0 (1/1840)
How can you calculate the specific charge? Giving all units
Specific charge (C/kg) = charge (C) / mass (kg)
Define atomic (proton number)
The number of protons in a nucleus = the number of electrons for an uncharged atom
Define nucleon number
The number of nucleons (protons + neutrons)
Define an isotope
An isotope is the same element with the same number of protons but different number of neutrons
Why is the strong nuclear force important?
It keeps nucleus stable
Sketch a graph of force against seperation for the strong nucear force.
Must be attractive and repulsive at different distance.
When is the strong nuclear force attractive
up to approximately 3 fm
When is the strong nuclear force repulsive
A distances closer than 0.5 fm
Describe some properties of the strong nuclear force
- Very strong - overcomes repulsion between positive protons
- Very short range - only acts between adjacent nucleons
- Acts on any nucleon (proton or neutron) and is independent of charge
- Can be attractive or repulsive Is repulsive if nucleons gets too close - stops nuclei collapsing
How does the strong nuclear force cause particles to be in equilibrium?
Increase in nucleon separation leads to an attractive force Decrease in nucleon separation leads to a repulsive force In both situations, force will return nucleons back to equilibrium position.
What are the three types of radioactive decay?
- Alpha
- Beta
- Gamma
Describe an alpha particle
- 2 protons and 2 neutrons or aHelium nucleus
- Relative mass of 4
- Relative charge of +2
- highly ionising
- Stopped by skin, paper, 5 - 10 cm of air
Describe a beta particle
- fast moving electron ejected from the nucleus
- Relative mass of almost 0
- Relative charge of -1
- moderately
- ionising Stopped by mm’s aluminium or 1 meter of air
Describe a gamma wave
- Electromagnetic wave that moves at the speed of light through a vacuum
- Relative mass of 0
- Relative charge of 0
- very weakly ionising
- Reduced by cm’s lead or m’s of concrete
Describe the changes that take place in beta decay
A neutron decays into a proton creating the beta particle and an electron antineutrino.
For a neutron to decay into a proton a down quark decays into a up quark
Describe the evidence that neutrinos exist
- Experimental data shows that as a beta particle is emitted in beta decay it will have a range of energies from nearly zero up to a maximum.
- All decays must have the same energy (conservation of energy)
- The total energy and momentum of the beta particle and recoiling nucleus was not constant.
- Energy has to be conserved Wolfgang pauli (1930) predicted a particle that could carry away the extra energy/momentum so they would be conserved. This particle was discovered and named the antineutrino
Describe the changes that take place in positron emission
A proton decays into a neutron creating the positron and an electron neutrino.
For a proton to decay into a neutron a up quark decays into a down quark.
Why does an antineutrino need to be released during beta decay
To conserve, energy, momentum and lepton number
Define a fundamental particle
Fundamental particles cannot be divided into other particles. They have no internal structure.
Give some examples of fundamental particles
Electron, neutrino, all quarks
What are the 6 types of quark
- Up
- down
- top
- bottom
- strange
- charm
What is the quark structure of a proton?
u u d
What is the quark structure of a neutron?
u d d
What is an antiparticle
particles with the same mass but opposite charge
State the name of the anti electron
Positron
Define a hadron
Hadrons are any particle made up of quarks.
Hadrons are not fundamental.
Hadrons can be either Baryons or mesons.
What force are hadrons subject to?
Strong nuclear force
Define a baryon
Baryons are made up of three quarks.
Common baryons are protons and neutrons and have a baryon number of 1
Which is the most stable baryon?
Proton
Define a meson
Mesons are classified as hadrons as they are made of quarks. Mesons contain a quark and an antiquark have a baryon number of 0
Name some typical mesons
Pions and Kaons
Name some leptons
Electrons, neutrinos, Tau, muon
What force controls leptons?
Leptons are subject to the weak nuclear force
In a nuclear event what must be conserved?
- Charge
- Baryon number
- Lepton number
- Energy
- Momentum
What force of nature creates strange particles?
Strange particles are made through the strong interaction
What force allows strange particles to decay?
Strange particles decay through the weak interaction (e.g. Kaons)
Why must strange particles be created in pairs?
To conserve strangness
When must strangeness be conserved?
When strange particles are made in pairs. Strangeness is conserved with the strong interaction (only the weak interaction can change the type of quark, so there must be the same number of strange particles before and after)
When can strangeness change?
Strangeness can change by +1, 0 or -1 in the weak interaction when a strange particles decay
Define annihilation
If a particle and anti-particle meet they will annihilate each other and their entire mass is converted into energy into the form of two identical gamma photons (e.g PET scanners)
During annihilation what is the minimum energy of one the gamma photons equal to?
The rest mass of one of the original particles
Minimum energy of each photon = Eo
Define pair production
In pair production a single photon vanishes and its energy is converted into mass in the form of a particle and its anti-particle.
What is the condition required for pair production?
This can only happen if the energy of the photon is enough to produce the (rest) mass of the particle and anti particle.
Min energy of photon = 2Eo
This normally happens near a nucleus to conserve momentum.
In pair productin what happens if the initial photon has an energy greater than the rest mass of the particels and anti particle?
The particle and anti particle take the extra energy away as kinetic energy
What is quark confinement?
The energy required to produce a separation of two quarks far exceeds the pair production energy of a quark-antiquark pair, so instead of pulling out an isolated quark, you produce mesons as the produced quark-antiquark pairs combine.
Define an exchange particle
Exchange particles are how forces act between two particles.
They are virtual particles and only exist for a very short amount of time.
They can transfer energy, charge force and momentum
For the strong nuclear force state:
the particles affected
the name of the exchange particle
its range
Nucleons (all hadrons)
Gluons and Pions
Range up to 3 fm
For the electromagnetic force state:
the particles affected
the name of the exchange particle
Range
Charged particles
Virtual photons
infinite range
For the weak nuclear force state:
the particles affected
the name of the exchange particle
Range
Responsible for beta decay and changing quarks e.g u to d
W+, W- bosons
10-18 m
For the gravitational force state:
the particles affected
the name of the exchange particle
Range
all particles with mass
Gravitron
Infinite
What are the rules for drawing particle interaction diagrams
Rules for drawing particle interaction diagrams:
- Exchange particles are represented by wiggly lines
- Other particles are represented by straight lines
- Incoming particles start at the bottom of the diagram and move upwards
- Baryons stay on one side of the diagram and leptons on the other
- The W boson carries charge from one side to the other (make sure charges balance)
- A W- particle going to the left has the same effect as a W+ moving to the right
What is electron capture?
Electron capture is a process in which the proton-rich nucleus absorbs an electron. This process thereby changes a nuclear proton to a neutron and simultaneously causes the emission of an electron neutrino
What is an electron-proton collision?
An electron collides at high speed with a proton. The proton decays into a neutron and an electron neutrino.
What are the similarities and differences between electron capture and electron-proton collisions?
Similarities - both change a nuclear proton to a neutron and simultaneously causes the emission of an electron neutrino
Differences - In electron-proton collision the electron is the particle thats acting because its being fired at a proton so the W boson comes from the elctron. It must be the W- (moving to the left) to conserve charge. With electron capture the exchange particel is the W+(moving to the right)
Sketch and label a Feyman diagram for electron repulsion.
See diagram
Sketch and label a Feyman diagram for beta decay (in terms of protons and neutrons)
See diagram
Sketch and label a Feyman diagram for beta decay (in terms of quarks)
See diagram
Sketch and label a Feyman diagram for positron emmision (in terms of protons and neutrons)
see diagram
Sketch and label a Feyman diagram for electron capture
see diagram
Sketch and label a Feyman diagram for electron - proton collision
see diagram
Sketch and label a feyman diagram for a neutrino and neutron interaction where a beta particle and proton are created
See diagram
Sketch and label a feyman diagram for a antineutrino and proton interaction where a positron and neutron are created
see diagram
