1.7 Particles - Particle Interactions Flashcards
The four interactions:
Electromagnetic
Strong nuclear
Weak nuclear
Gravitational
Electromagnetic:
Causes an attractive or repulsive force between charges
Gravitational:
Causes an attractive force between masses
Strong nuclear:
Causes an attractive (or repulsive) force between quarks (and so hadrons)
Weak nuclear:
Does not cause a physical force; it makes particles decay
Exchange particles:
Idea that interactions/forces between two particles are caused by ‘virtual particles’ being exchanged between the two particles
The general term for exchange particles is bosons
Strong nuclear exchange particle:
Gluon between quarks / pion between baryons; acting upon nucleons
Electromagnetic exchange particle:
Virtual photons acting upon charged particles
Weak nuclear exchange particle:
W+ / W- / Z on all particles
Gravitational exchange particles:
(gravitation?) on particles with mass
Range of strong nuclear:
3 x 10^-15
Range of electromagnetic:
infinite
Range of weak nuclear:
0.001 x 10^-15
Range of gravitational:
infinite
Relative strength of strong nuclear:
1
Relative strength of electromagnetic:
1 x 10^-3
The weak interaction:
A fundamental force that acts between all particles (hadrons and leptons) over a very short range
Only interaction that causes a quark to change flavour
Limited to beta minus, beta plus, electron capture, electron-proton collision
B- decay:
A down quark decays into an up quark; down quark emits a W- boson which decays into an electron and an electron-antineutrino
What does the W- boson do during beta- decay?
Transfers momentum, energy/mass and charge
As its emitted the nucleon recoils in order to conserve momentum
B+ decay:
An up quark decays to a down quark; up quark emits a W+ boson therefore turns into an up quark
W+ boson subsequently decays into a positron and an electron-neutrino
What does a W+ boson do during beta+ decay?
Transfers momentum, energy/mass and charge
As emitted the nucleon recoils in order to conserve momentum
Beta minus basic equation:
n -> p + e- + Ve^-
Beta plus basic equation:
p -> n + V + e+
Beta minus quark equation:
d->u
Beta plus quark equation:
u->d
Electron capture equation:
p + e- -> n + Ve
Electron proton collision equation:
p + e- -> n + Ve
Electron capture:
A proton in a proton-rich nucleus can turn into a neutron by interacting with an inner shell electron
In the nucleus an up quark emits a W+ boson
Boson is exchanged with electron which transfers momentum, mass/energy and charge so electron turns into electron neutrino
Electron proton collision:
Proton and electron collide at very high speed
Change occurs as a W- exchange from the electron to the proton
