Section 1- Particles Flashcards
What is specific charge?
The charge to mass ratio
charge/mass
C/kg
What is the relative mass of an electron?
0.0005
What letter is associated with a proton number?
Z
What is a nucleon?
A constituent of the nucleus - a proton or a neutron
What letter represents the nucleon number?
A
What is an isotope?
A version of an element with the same number of protons but a different number of neutrons
What is 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 force?
The fundamental force that keeps the nucleus stable by counteracting the electrostatic force of repulsion between protons
Describe the range of the strong force
- Repulsive - up to 0.5fm
- Attractive - from 0.5-3fm
- Negligible past 3fm
What makes a nucleus unstable?
Nuclei which have too many of either protons or neutrons or both
How do nuclei with too many nucleons decay?
Alpha decay - emission of a helium nucleus
How do nuclei with too many neutrons decay?
Beta minus decay - the neutron decays into a proton by the weak interaction and releases an electron and an anti-electron neutrino with the W- exchange particle
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
What is an alpha particle?
A particle that contains 2 protons and 2 neutrons, the same as a helium nuceus
What is an anti-particle
For each particle there is a corresponding anti-particle with the same rest energy and mass but all other properties are the opposite of its respective particle
What is the name of the anti-particle of an electron?
Positron
What is the anti-particle of a π0 (pion with 0 charge)?
π0 - its anti-particle is itself
What occurs when a particle and antiparticle meet?
Annihilation - the mass of the particle and antiparticle is converted back to energy in the form of 2 gamma ray photons which go in opposite directions to conserve momentum
What is pair production?
A gamma ray photon is converted into a particle-antiparticle pair
What is the minimum energy of a photon required to make a particle-anti-particle pair?
2 x rest energy of the particle
What are the 4 fundamental forces?
- Gravity
- Electromagnetic
- Weak nuclear
- Strong nuclear
The virtual photon is the exchange particle of which 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?
Charged objects
When does weak nuclear interaction occur?
When quark character changes (a quark changes into another quark), it affects all types of particles
What properties must be conserved in particle interactions?
- Energy
- Charge
- Baryon number
- Lepton number
- Momentum
- Strangeness (only for strong interactions)
Why do we need ensure strangeness is conserved in the strong interaction?
The quantum number reflects the fact that strange particles are always created in pairs
How can strangeness change in the weak interaction?
By 0, +1 or -1
What is a hadron?
- Baryons and mesons
- Made of 2 or more quarks held together by the strong nuclear force
What are the classes of hadrons?
- Baryons (3 quarks)
- Mesons (1 quark, 1 anti-quark)
The pion and kaon are both examples of which class of particle?
Mesons
What are the quark structures of pions and kaons?
π+ - ud¯
π− - du¯
π0 - u¯u or d¯d
K+ - us¯
K- - su¯
The pion can be an exchange particle for which force?
The strong nuclear force
What particle does a kaon decay into? Give 2 decay equations for this
A kaon always decays into a pion
K+ -> π+ + π0
or
K+ -> π+ + π+ + π-
Give some examples of baryons and their quark structures
- Protons - udu
- Neutrons - dud
What is significant about a proton?
- It is the only stable baryon
- All baryons will eventually deacy into protons
What are some examples of leptons?
- Electron
- Muon
- Neutrino
- Anti-particles of the above
What does a muon decay into?
An electron, an electron neutrino and a muon neutrino
What is the strangeness value of a strange quark?
-1
What are strange particles?
Particles that are produced through the strong interaction and decay through the weak interaction
What is the equation for electron capture?
p + e- -> n + Ve
