Unit 1.7) Particles and nuclear Physics Flashcards
What are the main constituents(parts)
of an atom?
Proton
Neutron
Electron
What is the letter associated with a proton number?
z
What is a nucleon?
A part of the nucleus: a proton or a neutron
What letter represents nucleon number?
A
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 protons, neutrons, or both.
Too many protons means the electrostatic force is too strong and pushes them apart.
Too many neutrons or both will make the nucleus larger than the range of the strong force, so it will no longer be held together
What is an anti-particle
For each particle there is an antiparticle which has the same rest energy and mass, the opposite charge, and will annihilate with the particle if they ever come in contact
True or false?
‘Every fundamental particle has a antiparticle
Can leptons and anti leptons combine together to form particles or can quarks and anti quarks combine together to form particles.
True
anti up quarks, anti down quarks.
anti electrons, anti neutrinos,
all anti particles have the same mass but opposite charge, ie electron goes from +1 to -1.
Leptons and anti leptons do not combine together and exist separately whereas quarks and antiquarks combine to to form composite subatomic particles known as baryons.
Antiparticle of an electron
Positron
What is the antiparticle of pion with neutral charge.
Its antiparticle is itself
Explain the process of annihilation
When a particle and its corresponding antiparticle come into contact with each other, they will annihilate.
The mass of the particle and antiparticle is converted back to energy in the form of 2 gamma ray photons which are released in opposite directions to conserve momentum.
What is pair production
When a gamma photon has sufficient energy, it can be converted into a corresponding particle-antiparticle pair
Name the four fundamental forces
Gravity
Electromagnetic/electrostatic
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
What does the electromagnetic force act on?
It acts on all charged objects. For example: when a positively charged ball repels another positively charged ball
When does the weak nuclear interaction occur?
When Quark character changes (a quark changes into another quark). It affects all type of particles
What properties must be conserved in particle interactions?
Energy
Charge
Baryon Number
Lepton Number
Momentum
Strangeness(only in strong interactions-it can change by + or -1 in weak interactions.
What is a lepton
A fundamental particle not made of quarks and does not experience the strong nuclear force
What is a hadron
A particle made of quarks that are held together by the strong force. Mesons and baryons are hadrons.
What are the classes of hadrons
Baryons(three quarks)
anti-baryons(three anti quarks)
Mesons(1Quark, 1 antiquark)
all baryons number is 1 all anti baryons number is -1.
All mesons have a baryon number of 0
The pion and kaon are both examples of which class of particle?
Mesons
The pion can be an exchange particle for which force?
The strong nuclear force.
What does a kaon decay into?
Pions
Give some examples of baryons
Proton-uud quark composition
Neutron-udd quark composition
What is significant about a proton
It is the only stable baryon.
All baryons will eventually decay into protons.
Examples of leptons
Electron, Muon, Neutrino,(all the above’s antiparticles)
What does a muon decay into
An electron, muon neutrino and electron antineutrino.
lepton numbers for electrons and muons before and after muon decay.
electron lepton number is zero before and after.
Lepton number for muons before and after is 1.
What is the strangeness value of a strange quark
-1
Is strangeness always conserved in the weak interaction.
No. Strangeness is only conserved in the strong interaction. In weak interactions it can change by 0,-1 or +1.
Strange particles are produced through the___ interaction and decay through the____ interaction.
Produced through the strong, decayed through the weak.
State the relative charge for an electron, electron neutrino, an up quark and a down quark.
Electron - 1
Electron neutrino: 0
Up quark: +2/3
Down quark: -1/3
What is the symbol for a positron
e^+ (or sometimes B^+ in beta decay)
Symbol for anti-up quark
__
U
What is the quark composition of a proton and neutron
Proton: uud
Neutron: udd(or ddu)
what is the first generation of quarks?
up quarks(u) and down quarks(u)
up quark charge is 2/3
down quark charge is -1/3
what is the first generation of leptons?
Electron(e^-) and electron neutrino(Ve)
Electron charge is -1
Electron neutrino charge is 0.
They both have a lepton number of 1 there anti particles have a lepton number of -1.
What are the two possible makeups of the neutral pion(pion=0)?
1)uu^-
Charge = +⅔ e + -⅔ e = 0
2)dd^- Charge = -⅓ e + +⅓ e = 0
How do you identify the force involved in a reaction?
Strong interactions (lifetime 10-24s)
Only hadrons are involved.
There is no change in quark flavour.
These are typically involved in collisions between particles.
Electromagnetic interactions (lifetime 10-12-10-18 s)
The particles must be charged or have charged components. Although a neutron is uncharged, it consists of charged quarks.
There is no change in quark flavour.
One or more photons may be emitted.
Weak interactions (lifetime 10-8 s)
Neutral leptons (neutrinos) are involved.
There may be a change in quark flavour.
What are the conservation laws for particles?
The baryon and lepton numbers must be conserved, the same before and after the decay of a particle.
It is important to consider the quarks involved in the reaction:
udd→uud+e
−
+
v
ˉ
e
In this reaction, one of the d quarks has changed to a u quark. This is known as a quark flavour change and, along with neutrino involvement, is exclusive to a weak interaction.
