Particle physics Flashcards
What is specific charge
Charge/mass
Q/m
Unit: ckg^-1
What is the strong nuclear force
A force that acts between nucleons (protons and neutrons)
- 0.5fm-3fm, SNF is attractive
- 0.5fm>, SNF is repulsive
- If there was no repulsion, the nuclei would collapse
- Attractive force must be stronger than the electrostatic force
- Works equally between all nucleons
- very strong force
Beta minus and beta plus decay
In beta minus decay, a neutron is converted into a proton, electron and electron antineutrino
In beta plus decay, a proton is converted to a neutron, positron and electron neutrino
Electron volts
- Another Unit for energy
- The work done when an electron accelerates through a p.d. of 1v
- J to eV= Divide by 1.6x10^-19
- eV to J = X by 1.6x10^-19
Neutrinos
- The neutrino is a particle, with no charge and no or almost no mass, which is the 3rd object involved in beta decay, which account for any ‘missing’ energy and maintains the conservation of energy during the decay.
- The neutrino must be neutral to maintain the conservation of charge.
- Sometimes the neutrino is the high energy particle and the electron is the low energy particle and vice versa.
Photons
-Electromagnetic radiation is absorbed and emitted in small packets of energy- these packets are called photons.
Photon energy= Planck’s Constant x Frequency
E= hf, can also be written as E=hc/lamda
-It’s impossible for matter to emit or absorb anything other than a complete photon of energy.
-A quantum of energy is directly proportional to the frequency of radiation.
Pair production
A photon of energy converted into matter and antimatter, e.g. a photon producing an electron and a positron.
For the to happen, the photon must have at least twice the amount of rest energy as 1 of the particles, 0.510999MeV in this case. So for the pair production of these two particles, a photon must have at least 1.021998MeV of energy.
-Therefore, hf=2E
Particle annihilation
- When 2 particles (matter and antimatter) collide to produce 2 photons, e.g. an electron and positron colliding to produce 2 photons.
- Therfore, 2E=2hf….. E=hf
Particle classification
Matter and Antimatter
-Hadron
-Baryon: Proton, Neutron- 3 quarks, SNF only affect
baryons
-Meson: Pion, Kaon- 1 quark and 1 antiquark
-Lepton
-Muon
-Electron
-Tau
- + their neutrinos and antiparticles
-Weak nuclear force affects everything
Fundamental forces
3 fundamental forces andtheir exchange particles
- Electromagnetic force: Photon
- Strong Nuclear Force: Pion
- Weak Nuclear Force: W boson
Exchange particles are transferred between 2 particles when a force acts between them
Quark structures
Proton: uud, antiproton: u ̅u ̅d ̅
Neutron: udd, antineutron: u ̅d ̅d ̅
Pion+: ud ̅, Pion-: u ̅d
Kaon+: us ̅, Kaon-: su ̅
Lepton Numbers
Each level of lepton is separate, so treat them separately. 1. Electron and positron 2.Muon and antimuon 3.Tau and antitau Particles: +1 lepton no. Antiparticles: -1 lepton no.
Particle interactions
Things that must be conserved in all particle interactions:
-Mass-energy
-Charge, Q
-Baryon no., B
-Lepton no., L
-Strangeness, S
-Strong interactions, change in S=0
-Weak interactions, change in S=1 or 0
-Momentum
E.g Beta minus decay
n = p e- Ve ̅ This is possible
Q: 0 1 0 0
B: 1 1 0 0
Le: 0 0 1 -1
S: 0 0 0 0The photoelectric effect
The release of electrons from a surface (usually metal) caused by light.
The photoelectric effect equations
hf=ϕ+Ek
- the moretightly bound electrons are, the more energy they require to be freed, and so end up with less kinetic energy
Threshold frequency:
hfo=ϕ
