Particles Flashcards
What are the main constituents of an atom
A proton, neutron, electron
What is meant by specific charge
Specific charge = charge/mass
Units C/kg
What is the specific charge of a proton
Charge: +1.6 x 10^-19
Mass: 1.67 x 10^-27kg
Specific charge: 9.58 x10^7 C/kg
What is the letter associated with the proton number?
Z
What is a nucleon?
The parts of a nucleus: a proton or a neutron.
What letter represents nucleon number?
A
What is the correct notation?
A Z
X X
Z A
A
X
Z
What is an isotope?
A version of an element with the same number of protons but a different number of neutrons.
State a use of radioactive isotopes.
Carbon dating - the proportion of carbon-14 in a material can be used to estimate 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?
Nucleus which have too many of either protons or neutrons or both.
How do nuclei with too many nucleons decay?
Alpha decay, which is the emission of a helium nucleus formed of 2 protons and 2 neutrons.
How do nuclei with too many neutrons decay?
Beta minus decay in which a neutron decays to a proton by the weak interaction (quark character has changed from udd to uud)
How was the existence of the neutrino hypothesised?
The energy of particles after beta decay was lower that before, a particle with 0 charge ( to conserve charge) and negligible mass must carry away this excess energy, this particle is the neutrino.
What is meant by beta minus decay?
When a neutron into a proton, the atom releases an electron and an anti-electron neutrino.
What is an alpha particle?
A particle contains two protons and two neutrons, the same as a helium nucleus.
What is an anti particle?
For each particle there is an antiparticle with the same rest energy and mass but all other properties are the opposite of its respective particle.
True of False:
Every particle has a antiparticle
True
What is the name of the antiparticle of an electron?
Positron
What is the antiparticle of a pion 0
Pion 0, since it is an antiparticle 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 proton-antiproton pair?
2 x proton rest energy:
2 x 938.257 = 1876.514 MeV
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 nucleus force?
Hadrons.
What is the exchange particle of the weak nuclear force?
The W boson
What does the electromagnetic force act on?
It acts on charged objects, for example when a positively charged ball repels another positively charged ball.
When does weak nuclear interaction occur?
When quark character changes
What properties must be conserved in particle interactions?
- Energy
- Charge
- Baryon number
- Lepton number
- Momentum
- Strangeness (only for strong interactions)
What is a hadron?
Both baryons and mesons are hadrons, hadrons are made of 2 or more quarks held together by the strong nuclear force.
What are the classes of hadrons?
- Baryons (three quarks )
- Mesons (1 quark, 1 antiquark)
The pion and kaon are both examples of which class of particles?
Mesons
The pions can be exchange particle for which force?
The strong nuclear force.
Which particle does kaons decay into?
A kaon decays into a pion.
Give some examples of baryons.
Proton - uud
Neutron - ddu
What is significant about a proton?
- It is the only stable baryon
- All baryons will eventually decay into protons
What are some examples of leptons?
- Electron
- Muon
- Neutrino
- (the antiparticles of the above)
What does a muon decay into?
An electron and two types of neutrino.
What is the strangeness value of a strange quark
- 1
True or False: ‘ strangeness is always conserved in a weak interaction’
False - strangeness is only conserved in the strong interaction, in weak interactions it can change by 0, -1 and +1
