Particle Physics Flashcards
Strong Nuclear Force
Range = 10^ -15 m (diameter of a U nucleus)
Affects = nuclear material
Purpose = binds nucleus
Relative magnitude = 1
Electro Magnetic Force
Affects = charged particles
Purpose = atomic bonding
Relative magnitude = 10^ -2
Weak Nuclear Force
Affects = all particles
Purpose = beta decay
Relative magnitude = 10^ -7
Gravitational Force
Affects = all particles
Purpose = attracts all matter
Relative magnitude = 10^ - 38
(does not affect sub atomic particles since masses are so small)
Ev to joules
ev ÷ 1.96 x 10^-19 = joules
joules to Ev
Joules x 1.96 x 10^-19 = ev
voltage to velocity
v = w/q
voltage x 1.96 x 10^-19 = energy in joules
E = 1/2 mv²
√ E ÷ 1/2 m = v
Momentum
E = 1/2 mv²
1) - for two particles to have equal
momentum
- Ek must be split inversely proportional to
their masses
(Ek ∝ 1/m)
2) - if particle at rest momentum = 0
- 2 particles will move off at equal momentums in opposite directions so net momentum = 0
- therefore ρ is conserved
Conservation
mass- energy: E = mc²
momentum: E = 1/2 mv² / (Ek ∝ 1/m)
charge: equal numbers of protons
Conservation in α decay
mass-energy: Mr U = Mr Th + Mr α + mc²
momentum: - U atom at rest
- Th and α move off in opposite
directions with equal
momentums inversely
proportional to their masses
so net ρ = 0
- α receives a larger portion of
disintegration energy
electric charge - U has 92 protons
- Th + α have 92 protons
Ernest Rutherford
- 1st artificial transmutation (α particles)
- N14 atoms bombarded with α radiation
- 7N14 + 2He4 = 8O17 + 1H1
- produced an isotope of oxygen and a
helium atom
artificial transmutation
when one element is deliberately converted into another element
Cockcroft + Walton
- 1st artificial transmutation using artificially accelerated particles (protons)
- could chose how and when to initiate transmutation
- lithium foil bombarded with protons in a linear accelerator
- helium atoms produced with Ek
- moved in opposite directions
- Ek from protons conserved
- 3Li7 + 1H1 = 2He4 + 2He4 + Ek (kinetic energy)
Linear accelerator
1) hydrogen discharge tube:
produces proton
2) proton injected into column
(evacuated tube)
3) accelerated - decreasing voltage supply
4) Li target @ 45° to the proton beam struck
5) 2 α particles produced moving 180° apart
to L + R of plate
6) detected on zinc sulfide screen - scintillation
7) microscope - flashes
O’Lawrence
cyclotron
- particle accelerator
- O motion: faster particles with lower voltage
colliding particles
- Coulomb force of repulsion must be over come
- extreme temperature + pressure
- high velocity collisions
= particle accelerators
colliding particles equation
p + p + Q1 = p + p + additional p + Q2
- Q1 = energy pf incident collision
- Q2 = energy of resultant collision
- additional p - depends on Ek of colliding
particles (protons)
Types of particle accelerators
linear - stanford
cyclotron - cern
combinations - Tevatron
cyclotron
- can independently accelerate particles in two rings and introduce them to collide when they wish
- O motion = more acceleration with less
voltage
neutrino
proposed : Pauli
- mass-energy not conserved
- zero charge so hard to find
found : Reines and Cowan
antimatter (positron)
proposed: Dirac
- eqn of E has √
- therefore + and - answer
found: Hess + Anderson (proof of positron)
antimatter
- particles with identical mass
- opposite spin
- takes E to create p + anti p (pair production)
- releases E when p + anti p brought back
together (pair annihilation)
Pair production
- the simultaneous creation of a particle and its corresponding antiparticle from electromagnetic energy
- hf = 2(mc² ) + Ek1 + Ek2
- photon = particle + antiparticle
Threshold energy
- minimum energy required for pair production to occur
- if hf = threshold energy particles created at rest
- if hf > threshold energy, extra = Ek
conservation of momentum in pair production
- particles do not move 180° apart
- shows that gamma ray has momentum
as p conserved and net p does not equal 0
Pair Annihilation
the conversion of a particle and its corresponding anti-particle into electromagnetic energy
2(mc²) + Ek1 + Ek2 = 2hf
- particle + antiparticle = 2 photons !!!
- photons produced in pairs to conserve
momentum
- each photon of equal energy + frequency
!!greater mass = more energy!!
eg. proton annihilation > electron
Quark
- an elementary particle which experiences all four fundamental forces and forms a basic constituent of mater
- fundamental particle
- feels strong nuclear force
Murray Gell-Mann
- discovered quarks
- James Joyce’s Finnegan’s wake
- “three quarks for a muster mark”
6 quarks/ antiquarks
up down top bottom strange charm
Leptons
- not made up of quarks
- do not feel strong nuclear force
- principle force = weak nuclear
- fundamental elementary particles
electron (-1) (e-)
muon (-1) (μ)
tao (-1) (τ)
positron (+1) (e+) (anti-electron)
(positively charged electron)
electron neutrino (0) (Ve)
anti electron neutrino (O)
Hadrons
- made up of quarks (not fundamental)
- feel all four forces
Mesons
- Mr between electron and proton
- made up of 1 quark and 1 different
antiquark - pion (u,D) (+1) (π+)
- kaon (D,s) (0) (κ°)
pion
quarks = up, anti-down charge = +1 symbol = π+
kaon
quarks = anti-down, strange charge = 0 symbol = κ°
Baryons
- Mr greater than or equal to a proton
- made up of 3 quarks / 3 anti-quarks
- proton (uud) (p+) = +1
- neutron (udd) (n°)= 0
- lambda (udc) (Λ+) = +1
- sigma (dds) (Σ-) = -1
proton
quarks = up, up, down charge = + 1 symbol = p+
neutron
quarks = up, down, down charge = 0 symbol = n°
lambda +
quarks = up, down, charm charge = +1 symbol = Λ+
sigma -
quarks = down, down, strange charge = -1 symbol = Σ-
anti-proton
quarks = anti-up, anti-up, anti-down charge = - 1 symbol = p -
physical quantity the same for quark and antiquark
mass
magnitude of charge
physical quantity different for quark and antiquark
sign of charge
spin
beta decay (including neutrino)
1N1 = 1H1 + -1e0 + ve
maximum frequency of a photon that can form an electron and a neutron by pair production
hf = 2mc² f = 2mc²/h
why does high speed particle travel in circular motion when it enters a magnetic field?
force of the magnetic field is perpendicular to the velocity of the particle
minimum frequency of photon produced by pair annihilation
2mc² = 2hf mc² = hf f = mc²/h
why will the photons have more than the minimum energy?
in addiction to the rest mass the colliding particles will have kinetic energy
why must particles travel at high speeds?
to overcome the coulomb force of repulsion
why can two positrons not annihilate eachother
in conflict with conservation of charge
