2.1 Particles Flashcards
What is meant by Specific Charge?
The Charge to Mass ratio:
Specific Charge = charge/mass
Units: C/kg
What is Nucleon?
A constituent of the nucleus : proton or neutron
What is an isotope?
A version of an element with the same number of protons ,but different numbers of neutrons
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 strong nuclear?
the fundamental force that keeps the nucleus stable by counteracting the electrostatic repulsive force between protons
Describe the range of the strong force.
1) repulsive up to 0.5fm
2) attractive from 0.5-3fm
3) negligible past 3fm
What makes a nucleus unstable?
Nuclei with either too many of either protons or neutrons
How do nuclei with too may nucleons decay?
Alpha decay (emissions of helium nucleus - 2 protons and 2 neutrons)
How do nuclei with too many neutrons decay?
Beta minus decay in which the neutron decays into a proton b the weak interaction (quark character has changed from udd to uud )
How was the existence of the neutrino hypothesised?
the energy of the particles after beta decay was lower than before, a particle with 0 charge (to conserve charge) and negligible mass has to carry away the excess energy , this is the neutrino
What is meant by beta minus decay?
When a neutron turns into proton , the atom releases an electron and an anti-electron neutrino
What is an anti particle?
For each particle there is an anti particle , they have the same rest energy and mass , but everything else is opposite so they have the opposite charge
What occurs when a particle and an anti-particle meet?
Annihilation:
The mass of the particle and anti-particle is converted into energy in the form of 2 gamma ray photons going in opposite directions to conserve momentum
What is pair production?
A gamma ray photon is converted into a particle anti-particle pair
What is the minimum energy of a photon needed to make a proton antiproton pair?
2x proton rest energy
Unit:eV
Name the 4 fundamental forces?
1) Gravity
2) Electromagnetic
3) Weak nuclear
4) Strong nuclear
The virtual photon is the exchange particle between what force?
The electromagnetic force
What type of particles are affected by the strong nuclear force?
Hadrons
What is the exchange particle of the weak nuclear force?
The W boson (W+ or W-)
What does the electromagnetic force act on?
Any particle with a charge
When does the weak interaction occur?
When the quark character changes (when a quark turns into another quark), it affects all kinds of particles
Which properties must be conserved in particle interactions?
1) Energy
2) Charge
3) Baryon number
4) Lepton number
5) Momentum
6) Strangeness (only for strong interactions)
What is a hadron?
Both baryons and mesons are hadrons , they consist of 2 or more quarks held together by the strong nuclear force
What are the classes of hadrons?
1) Baryons (3 quarks)
2) Mesons (1 quark 1 anti-quark)
The pion can be the exchange particle of what force?
The strong nuclear force
What particle does a kaon decay into?
A kaon decays into a pion
What is significant about a proton?
1) Only stable baryon
2) All baryons decay into protons
What are some examples of leptons ?
1) Electron
2) Muon
3) Neutrino
4) all antiparticles of the above
What does a Muon decay into?
An electron
What is the strangeness value of a strange quark?
-1
Is strangeness conserved in the weak interaction?
No ,strangeness is only conserved in the strong nuclear interaction , in the weak interaction it can change by 0,-1 or +1
Electron capture
A proton captures an inner shell electron and becomes a neutron and an electron neutrino with the W+ boson as the exchange particle
Electron and proton collision
Electron and proton collide and a W- boson particle is exchanged. Electron turns into an electron neutrino and the proton becomes a neutron
