2.3 Particles and radiation - Conservation laws & particle interactions Flashcards
What are the 4 fundamental interactions or fundamental forces?
- Gravity
- electromagnetism
- strong nuclear
- weak nuclear
What are the ranges of the fundamental forces?
- electromagnetic and gravitational intereactions have infinite range
- weak force has a range of up to 10^-18
- strong force has a range of up to 10^-15
What is the order of strength from strongest to weakest for the fundamental forces?
- strong
- electromagnetism
- weak
- gravitational
What are the properties of the fundamental forces?
- gravitational only affects particles with mass
- electromagnetic affect particles with charge
- weak interaction affects all particles
- strong interactions only effect hadrons
What is another word for exchange particles?
visual particles
Why must exchange particles exist?
when two particles interact
- there cannot be instantaneous action at a distance
- this means one particle needs to know that the other is there
How are virtual particles created?
- two particles exert force on each other
What are virtual particles?
- exist for a short time
- carry the fundamental force between each particle
What is the electromagnetic force?
forces that only occur between charged particles
What is the exchange particle that carries the electromagnetic force?
virtual photon
What are the properties of the photon?
- has no mass
- has no charge
- is its own antiparticle
When do electromagnetic interactions occur?
Whenever two charged particles interact with each other
Why are electromagnetic forces responsible for binding to atoms?
due to the attractive force between the negative electron and positive nucleus
What are the exchange particle of the strong nuclear forces interactions, and when are they used?
- the pion - between nucleons
- the gluon - between quarks
What are the weak interactions responsible for?
the radioactive decay of atoms
What is the exchange particles responsible for weak interactions?
W-
W+
Z0
bosons
What occurs in Beta - decay and what is it an example of?
- e.g. of weak interaction in action
- a neutron turns into a proton emitting an electron and an anti-electron neutrino
- The W- boson is the exchange particle in this interaction
What occurs in beta plus decay?
- proton turns into a neutron
- emitting a positron and an electron neutrino
- the W+ boson is the exchange particle in this interaction
What occurs when electrons and protons area attracted to each other via the electromagnetic interaction?
- they interact with each other, it is the weak interaction that facilitates the collision
What is the electron capturer and electron - proton collisions decay equation?
proton + electron -> neutron + electron neutrino
What is electron capture?
- when an atomic electron is absorbed by a proton in the nucleus
- resulting in the release of a neutron and a electron neutrino
- the decay is mediated by the W+ boson
What is electron-proton collisions?
- when an electron collides with a proton
- a neutron and electron neutrino are emitted
- this decay is mediated by the W- boson
What is a Feynman diagram?
a clear way of representing particle interactions in terms of their incoming and outgoing particles and exchange particles
What are the rules of a Feynman diagram?
- vertical axis represents time
- horizontal axis represents space
- gauge bosons are represented by a savvy or dashed lines or a helix
- all other particles are represented by a wavy or dashed lines or a helix
- all other particles are represented by straight lines
- each line apart from neutral bosons can have an error with its direction forward in tie
- the total charge, baryon number and lepton number must be conserved at each vertex
- particle lines must not cross over
How are exchanged particles represented in Feynman diagrams?
- the weak interaction, W and Z bosons are represented by a wavy line
- W+ and W- can have an error showing their direction or must be slanted upwards, meaning that they are forward in time
- pions are represented by a wavy or dashed line
- photons are represented by a wavy line
- gluons are represented by a helix
How is the sign of the W particle determines?
- dependent on the other particles involved in the decay
- because charge must be conserved at each vertex, if a neutron turns into a proton the W- carries away a negative charge from the neutral neutron, leaving a positive charge of the proton
- negative charge is the carried to the vertex with the electron and anti-neutrino
What is the quark transformation in beta decay?
- occurs due to weak interaction between the quarks
- when a neutron turns into a proton emitting an electron and anti-electron neutrino
- this happens by turning a down quark into an up quark
- the W- boson carries the negative charge of the down quark providing the negative charge for the electron and anti - neutrino
What is the quark composition in Beta plus decay?
- when a proton turns into a neutron emitting a positron and an electron neutrino
- proton turns into a neutron because an up quark turns into a down quark
- W+ boson carries the positive charge of the up quark providing a positive charge for the positron and neutrino
In particle interactions, what conservation laws must be obeyed?
- charge
- baryon number
- lepton number
- strangeness
- energy
- momentum
What is the exception in conservation laws?
Strangeness does not need to be conserved in weak interactions
