Particles Flashcards
Nucleons
Protons + neutrons
Isotopes
Have the same number of protons but a different number of neutrons
Unit of specific charge
C/kg
“specific” meaning
Amount of something per unit mass
Specific charge (charge to mass ratio)
Charge / mass
Do the electrons need to be included in specific charge calculations?
No, but it must be noted that their mass in negligable
Use of specific charge
Identifying unknown particles
Rest mass
The mass of an object when it is stationary
Rest energy
The energy of an object when it is stationary (also called minimum energy)
How is mass effected by an objects motion?
A moving object has greater KE, so it has a slightly greater mass
Particles and Anti-particles
Every particle has a corresponding anti-particle. Both have the same mass, but opposite values for charge or some other important property.
Annihilation
Occurs when a particle meets its own anti-particle. All the mass is converted to photons of energy - two photons moving in opposite directions must be created to conserve momentum.
Pair production
One photon of sufficient energy may provide the mass to produce a particle-anti-particle pair.
What is additional energy converted to in annihilation and pair production?
Kinetic energy
Four fundamental forces
- Gravity
- Electromagnetic
- Strong nuclear force
- Weak nuclear force
Electromagnetic force
Effects charged objects (responsible for most everyday forces)
Strong nuclear force
Holds together nucleons as well as the quarks inside each proton and neutron.
Weak nuclear force
Responcible for beta decay, effects hadrons, leptons and neutrinos (only force to effect neutrinos)
Range where strong force is attractive
0.5fm to 3fm
Range where strong force is repulsive
<0.5fm
When does the strong force = 0?
> 3fm
What prevents the nucleus from collapsing?
The strong force becomes repulsive when nucleons get too close
Why is it clear that the strong force only acts over a very small range?
Different sized nuclei have the same density (no cumulative squashing effect as nucleons are only attracted to their immediate neighbors)
What makes a nucleus unstable?
Having too many protons relative to the number of neutrons (there are not enough neutral particles to separate the protons and reduce the effect of the repulsion)
Alpha particle
2 protons + 2 neutrons (helium nucleus)
Two main categories of particle
Hadrons and leptons
Two categories of hadrons
Baryons and mesons
Which particles are baryons?
Protons and neutrons
Which particles are measons?
π-mesons (pions) and k-mesons (kaons)
Which particles are leptons?
Electrons, muons and their associated neutrinos
What are hadrons made up of?
Quarks
Baryon/Lepton number of a particle?
1= Is a baryon/lepton
-1 = Is an anti-baryon/anti-lepton
0 = Not a baryon/lepton
Which quantum numbers are conserved interactions?
Charge
Baryon number
Lepton number
Hadrons
The only particles which experience the strong nuclear force. Made of quarks and antiquarks. They are baryons or mesons.
Baryons
Consist of 3 quarks (qqq). Anti-baryons consist of 3 antiquarks (q̅q̅q̅)
Mesons
Consist of a quark and an antiquark (qq̅)
Which particle is its own antiparticle?
Π⁰
Which particle has the greatest specific charge?
Electrons
What is the only stable baryon?
Protons (all other baryons will decay to protons eventuly)
Quark structure of a proton
uud
Quark structure of a neutron
udd
Leptons
Leptons are fundamental particles - they are not made up of any simpler bits
Muons
Same charge as an electron but is much heavier.
What forces do leptons experience?
- Weak nuclear force
- Electromagnetic force (charged particles)
What forces do hadrons experiance?
- Strong nuclear force
- Weak nuclear force
- Electromagnetic force (charged particles)
Where do a lot of neutrinos come from?
Nuclear reactions in the sun
Strange particals
Created by the strong interaction, decay by the weak interaction. Contain strange quarks.
When is strangeness conserved?
Conserved in the strong interaction
Not conserved in the weak interaction
How can the strangeness change?
By +1 or -1
Exchange particles
Transfer energy, momentum, force, and sometimes charge between interacting particles
Exchange particles for strong nuclear force between hadrons
Pi-measons
Exchange particles for weak nuclear force
W+ and W- bosons
Exchange particles for electromagnetic force
Photons
Why are exchange particles virtual particles?
They only exist for a short time and can’t be detected without interfering with their behavior.
Vertical direction a Feynman diagram
Time
Horizontal direction on a Feynman diagram
Space
Why can’t a particle move downwards on a Feynman diagram?
It would be moving backwards in time
What interaction causes beta decay?
The weak interaction
What is electron capture?
An unstable nucleus captures an orbiting electron turning a proton into a neutron and an electron neutrino to become more stable
Why is an x-ray emitted after electron capture?
An electron moves down energy levels to fill the gap left by the electron involved in the interaction
What is beta- decay?
A neuron turns into a proton, an electron and an anti-electron-neutino
Evidence for the antineutrino in beta- decay
Beta particles are emitted with a range of energies. The same energy is given out in each decay but it is unevenly distributed between the products.
What is a ß- particle?
High energy electron emitted from the nucleus
What is a ß+ particle?
A high energy positron emitted from the nucleus
What is beta+ decay?
Where a proton becomes a neutron, a positron and a neutrino
What is an alpha partical?
A helium nucleus (2 protons + 2 neutrons)
What are the 3 types of fundamental partical?
- Leptons
- Bosons
- Quarks
Relative mass of an electron
0.0005
