2.1 Particles Flashcards
What is a nucleon?
A constituent of the nucleus: a proton or a neutron
State a use of radioactive isotopes
Carbon dating - the proportion of carbon-14 in a material can be used to estimate its age
What is the SNF?
Fundamental force that keeps the nucleus stable by counteracting the electrostatic force of repulsion between protons
Describe the range of the SNF
- repulsive up to 0.5fm
- attractive from 0.5-3fm
-Negligible past 3fm
What makes a nucleus unstable
Nuclei that have too many of either protons or neutrons or both
How do nuclei with too many nucleons decay?
Alpha decay
How do nuclei with too many neutrons decay?
Beta minus decay in which a neutron decays to a proton by the weak interaction ( udd to uud)
What is meant by beta-minus decay?
When a neutron turns into a proton, the atom releases an electron and an anti-neutrino
What occurs when an anti-particle and particle meet
Annihilation
What is the decay of americium-241 used for?
Smoke alarms
What is the decay of polonium-210 used for?
Ionisers
What force is responsible for beta decay?
The weak force
What does the weak force act on?
Leptons and hadrons
When does beta decay occur?
When the nucleus emits an electron or a positron
Why it called β- decay when a neutron decays into a proton?
An electron is produced
Why is it called β+ decay when a proton decays into a neutron?
A positron is produced
What happens to the unaccounted-for energy in beta decay?
It is carried away by the neutrinos
What happens if the nucleus is still unstable after emitting alpha or beta radiation?
It is in an excited state, and gives off gamma radiation
Why was the existence of the neutrino hypothesised?
To account for conservation of energy in beta decay
What type of particle are neutrinos?
Leptons
When are electromagnetic waves emitted?
When a charged particle loses energy
When can a charged particle lose energy (and an electromagnetic wave emitted as a result)?
when a fast moving electron is stopped, slows down or changes direction
when electrons move to a lower energy shell
In what form is electromagnetic radiation emitted?
Photons - bursts or packets of energy
What is one electron volt defined as?
The energy transferred when an electron is moved through a p.d. of 1V
What is annihilation
The mass of particle and antiparticle is converted back to energy, producing 2 gamma ray photons that go in opposite directions to conserve momentum
What is pair production
A gamma ray photon is converted into a particle-antiparticle pair
For pair production to take place the photon has to have an energy equal to or greater than
a certain minimum energy. Explain why there is a minimum energy.
energy of photon needs to provide at least the rest masses of both particles
What is the minimum energy of a photon required to make a proton-antiproton pair?
2 x proton rest energy
2 x 938.257 = 1876.514 MEV
Name the 4 fundamental forces?
- Gravity
- Electromagnetic
- Weak nuclear force
- Strong nuclear force
The virtual photon is the exchange particle of which force?
Electromagnetic
What type of particles are affected by the strong nuclear force?
Hadrons
Exchange particle of weak nuclear force
W boson ( W+ or W- )
What does the Electromagnetic force act on?
it acts on charged objects, for example when a positively charged ball repels another positively charged ball
When does weak nuclear interaction occur?
When quark interaction changes, it affects all types of particles
Which properties must be conversed in particle interactions? (6)
- energy
- charge
- baryon number
- lepton number
- momentum
- strangeness (only for strong interactions)
What is a hadron?
composite particles that are made only of quarks (or antiquarks). The experience the strong nuclear force.
What particles does the strong interaction affect?
hadrons feel the strong force only
What is the exchange particle for strong interaction? what particles does the strong interaction affect?
- gluon (for quarks)
- pion (for nucleons)
hadrons feel the strong force only
What is minimum energy required by the photon in pair production?
The rest energy of the particle pair
Why do protons repel when they approach each other?
Due to the electromagnetic interaction and the exchange of a virtual photon
Which quarks are antiprotons made up of?
Two antiup quarks and one antidown quark
What is a muon?
A heavier relative of the electron
How do hadrons decay?
Weak interaction
What is the only stable baryon?
Protons
Draw the classification of particles
What is the rest energy of a particle?
The “energy equivalent” of the particle’s mass.
What is an antiparticle?
A corresponding particle to a particle with the same mass and rest energy, but opposite charge.
What is beta-plus decay? (2)
- 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.
When can pair production happen?
When the photon has enough energy to produce the mass of the particle and antiparticle.
Which photons have enough energy to produce mass through pair production?
Gamma ray photons.
Where does pair production usually happen and why?
Near the nucleus, which helps conserve momentum.
The minimum energy of a photon in pair production is equal to…
…the total rest energy of the particles produced.
What particles are affected by the weak nuclear force?
All types
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.
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.
What are hadrons?
Particles that feel the strong nuclear force. They are not fundamental.
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
What are leptons?
Particles that do not feel the strong interaction. They are fundamental.
How do strange particles (e.g. kaons) interact?
- Created by the strong interaction * Decay via the weak interaction
What is unusual about strangeness?
- It is not ALWAYS conserved
What is the exchange particle for electromagnetic interaction? what particles are affected?
- A virtual Photon γ. has zero rest mass + infinite range
- only charged particles are affected
What is the exchange particle for weak interaction? what does it affect?
The weak interaction exchange particle is the W boson.
The weak force affects all particle types.
Generally, what happens when two particles interact?
They exert equal and opposite forces on each other
Units for specific charge?
Ckg⁻¹
What is equilibrium separation?
A point when the resultant force is zero and the attractive and repulsive forces balance
what are the mesons quark compositions?
What is the relative charge of protons, neutrons and electrons?
- Protons = +1 * Neutrons = 0 * Electrons = -1
What is the relative mass of protons, neutrons and electrons?
- Protons = 1 * Neutrons = 1 * Electrons = 0.0005
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
Is the interaction between two distant objects instantaneous?
No - this is explained by the need for exchange particles, which cause forces.
Why is an antineutrino produced in beta-minus decay, while a neutrino is produced in beta-plus decay?
To conserve lepton number.
What is the difference between pions and kaons?
Pions - Lighter, less unstable, not strange * Kaons - Heavier, more unstable, strange
What is quark confinement?
The idea that quarks cannot exist not their own.
Describe the mass, range and charge of a W boson.
- Non-zero rest mass * 0.001fm range * Can be positively or negatively charged
Feynmann diagram for B-
Feynmann diagram for B+
Feynmann diagram for electronic capture
Feynmann diagram for electron-proton collision
Feynmann diagram for Electromagnetic repulsion
range of strong nuclear force
10^-15
