2.1 Particles Flashcards
What are the main constituents of an atom?
- Proton
- Neutron
- Electron
What is specific charge?
Specific charge=charge/mass
Units C kg-1<\sup>
Also known as Charge to Mass ratio
Define nucleon.
A constituent particle of a nucleus. Either a proton or a neutron.
What is nuclide notation?
- X is the element
- A is the nucleon or mass number (protons + neutrons)
- Z is the proton number (or relative charge)
Define isotope.
Atom of an element with different number of neutrons and the same number of protons.
What is the strong nuclear force?
The fundamental force that binds nucleons together and stable in a nucleus.
What is the range and behaviour of the strong force?
- Repulsive 0-0.5 fm
- Attractive 0.5-3 fm
- Negligible >3fm
What makes a nucleus unstable?
Too many nucleons; either protons, neutrons, or both.
A unstable nucleus wants to become a lighter stable nucleus by releasing energy.
How do nuclei with too many nucleons decay?
Alpha decay
Where an alpha particle is a Helium nucleus
How do nuclei with too many neutrons decay?
Beta minus decay
Where a beta minus particle is an electron
How do nuclei with too many protons decay?
Beta plus decay
Where a beta plus particle is a positron
How was the existence of the neutrino hypothesised?
The energy of particles after beta decay was lower than before, a particle with 0 charge (to conserve charge) and negligible mass must carry away this excess energy, this particle is the neutrino.
True or false:
‘Every particle has a corresponding antiparticle’
True
What properties are different between a particle and its antiparticle?
All properties/quantum numbers are opposite except mass
For example: charge and strangeness
What are the antiparticles for
* proton
* neutron
* electron
* neutrino
- antiproton
- antineutron
- positron
- antineutrino
What is the photon model of EM radiation?
EM radiation consists of discrete packets (quanta) of energy
What is the equation for photon energy?
What do the letters represent in this equation?
What is annilihation?
When a particle and its corresponding antiparticle meet, resulting in 2 gamma photons
For example
What is the minimum energy of 1 of the gamma photons in an annilihation?
Photon energy equals the rest energy of the particle
What is pair production?
When a gamma photon passes near a nucleus and produces a particle-antiparticle pair.
For example
What is the minimum energy of the gamma photon in pair production?
Photon energy equals twice the rest energy of the particle
What are the 4 fundamental forces/interactions?
- Gravity
- Electromagnetic
- Weak
- Strong
What is an exchange particle/Boson?
A particle that transfers force between elementary particles
What is the exchange particle for Electromagnetism?
(Virtual) Photon
What particles does the Electromagnetic force act on?
Charged particles
For example: EM will act on a proton but not a neutron
What are the exchange particles for the Weak force?
W+ and W- bosons
When does the Weak force occur?
When there is a change in quark flavour
A way to identify a Weak interaction is if there are neutrinos present.
What are the exchange particles for the Strong Nuclear force?
Pions
What particles does the Strong force act on?
Hadrons
What is the Feynman diagram for the scattering of 2 electrons?
What is a hadron?
- Baryons and Mesons are hadrons
- Baryons are 3 quark
- Mesons are a quark-antiquark
- Bound by the Strong force
Hadrons are not fundamental particles
What quantum number is associated with Baryons?
Baryon number.
Baryon number must be conserved.
What is significant about the proton?
It is the only stable Baryon
Because it is the lightest Baryon. All Baryons decay towards protons.
Protons only decay when in a nucleus!
What class of particles are Pions and Kaons?
Mesons
What particle does a Kaon decay into?
Pion (plus other particles)
Think of the Kaon as a heavy cousin of the Pion.
What are the Leptons?
- Electron
- Muon
- Electron Neutrino
- Muon Neutrino
Only feel the Weak force, and the chraged leptons also feel the EM force
What quantum number is associated with Leptons?
Lepton number
There is also Lepton flavour number. All of which must be conserved.
What does a Muon decay into?
Electron (plus other particles)
Think of the Muon flavours as heavy cousins of the electron flavours
What do strange partices contain that non-strange particles do not?
At least one strange quark (or antiquark)
For example: the Kaons
In what interactions are strange particles produced?
Strong interactions
In what interactions do strange particles decay?
Weak interactions
What quantum number is associated with strange particles?
Strangeness
Strange quark has -1 strangeness
Antistrange quark has +1 strangeness
What force violates the conservation of strangeness?
Weak force
Strangeness can change by -1, 0, or 1 in weak interactions
What are the quark compositions of the proton and the neutron?
- Proton is uud
- Neutron is udd
What are the quark compositions of the pions?
What are the quark compositions of the kaons?
Write the decay equation for the neutron.
This is a beta minus decay
What are all the conservation laws?
- Energy
- Momentum
- Charge
- Baryon number
- Lepton number
- Strangeness
Strangeness is violated by the Weak interaction
