Particle Physics

Question 1

Strong Nuclear Force

Answer 1

Range = 10^ -15 m (diameter of a U nucleus)
Affects = nuclear material
Purpose = binds nucleus
Relative magnitude = 1

Question 2

Electro Magnetic Force

Answer 2

Affects = charged particles
Purpose = atomic bonding
Relative magnitude = 10^ -2

Question 3

Weak Nuclear Force

Answer 3

Affects = all particles
Purpose = beta decay
Relative magnitude = 10^ -7

Question 4

Gravitational Force

Answer 4

Affects = all particles
Purpose = attracts all matter
Relative magnitude = 10^ - 38

(does not affect sub atomic particles since masses are so small)

Question 5

Ev to joules

Answer 5

ev ÷ 1.96 x 10^-19 = joules

Question 6

joules to Ev

Answer 6

Joules x 1.96 x 10^-19 = ev

Question 7

voltage to velocity

Answer 7

v = w/q
voltage x 1.96 x 10^-19 = energy in joules
E = 1/2 mv²
√ E ÷ 1/2 m = v

Question 8

Momentum

Answer 8

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

Question 9

Conservation

Answer 9

mass- energy: E = mc²

momentum: E = 1/2 mv² / (Ek ∝ 1/m)
charge: equal numbers of protons

Question 10

Conservation in α decay

Answer 10

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

Question 11

Ernest Rutherford

Answer 11

• 1st artificial transmutation (α particles)
• N14 atoms bombarded with α radiation
• 7N14 + 2He4 = 8O17 + 1H1
• produced an isotope of oxygen and a
  helium atom

Question 12

artificial transmutation

Answer 12

when one element is deliberately converted into another element

Question 13

Cockcroft + Walton

Answer 13

• 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)

Question 14

Linear accelerator

Answer 14

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

Question 15

O’Lawrence

Answer 15

cyclotron

• particle accelerator
• O motion: faster particles with lower voltage

Question 16

colliding particles

Answer 16

• Coulomb force of repulsion must be over come
• extreme temperature + pressure
• high velocity collisions
  = particle accelerators

Question 17

colliding particles equation

Answer 17

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)

Question 18

Types of particle accelerators

Answer 18

linear - stanford
cyclotron - cern
combinations - Tevatron

Question 19

cyclotron

Answer 19

• can independently accelerate particles in two rings and introduce them to collide when they wish
• O motion = more acceleration with less
  voltage

Question 20

neutrino

Answer 20

proposed : Pauli
- mass-energy not conserved
- zero charge so hard to find
found : Reines and Cowan

Question 21

antimatter (positron)

Answer 21

proposed: Dirac
- eqn of E has √
- therefore + and - answer
found: Hess + Anderson (proof of positron)

Question 22

antimatter

Answer 22

• 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)

Question 23

Pair production

Answer 23

• the simultaneous creation of a particle and its corresponding antiparticle from electromagnetic energy
• hf = 2(mc² ) + Ek1 + Ek2
• photon = particle + antiparticle

Question 24

Threshold energy

Answer 24

• minimum energy required for pair production to occur
• if hf = threshold energy particles created at rest
• if hf > threshold energy, extra = Ek

Question 25

conservation of momentum in pair production

Answer 25

- particles do not move 180° apart - shows that gamma ray has momentum as p conserved and net p does not equal 0

Question 26

Pair Annihilation

Answer 26

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

Question 27

Quark

Answer 27

- an elementary particle which experiences all four fundamental forces and forms a basic constituent of mater - fundamental particle - feels strong nuclear force

Question 28

Murray Gell-Mann

Answer 28

- discovered quarks - James Joyce's Finnegan's wake - "three quarks for a muster mark"

Question 29

6 quarks/ antiquarks

Answer 29

``` up down top bottom strange charm ```

Question 30

Leptons

Answer 30

- 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)

Question 31

Hadrons

Answer 31

- made up of quarks (not fundamental) | - feel all four forces

Question 32

Mesons

Answer 32

- Mr between electron and proton - made up of 1 quark and 1 different antiquark - pion (u,D) (+1) (π+) - kaon (D,s) (0) (κ°)

Question 33

pion

Answer 33

``` quarks = up, anti-down charge = +1 symbol = π+ ```

Question 34

kaon

Answer 34

``` quarks = anti-down, strange charge = 0 symbol = κ° ```

Question 35

Baryons

Answer 35

- 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

Question 36

proton

Answer 36

``` quarks = up, up, down charge = + 1 symbol = p+ ```

Question 37

neutron

Answer 37

``` quarks = up, down, down charge = 0 symbol = n° ```

Question 38

lambda +

Answer 38

``` quarks = up, down, charm charge = +1 symbol = Λ+ ```

Question 39

sigma -

Answer 39

``` quarks = down, down, strange charge = -1 symbol = Σ- ```

Question 40

anti-proton

Answer 40

``` quarks = anti-up, anti-up, anti-down charge = - 1 symbol = p - ```

Question 41

physical quantity the same for quark and antiquark

Answer 41

mass | magnitude of charge

Question 42

physical quantity different for quark and antiquark

Answer 42

sign of charge | spin

Question 43

beta decay (including neutrino)

Answer 43

1N1 = 1H1 + -1e0 + ve

Question 44

maximum frequency of a photon that can form an electron and a neutron by pair production

Answer 44

``` hf = 2mc² f = 2mc²/h ```

Question 45

why does high speed particle travel in circular motion when it enters a magnetic field?

Answer 45

force of the magnetic field is perpendicular to the velocity of the particle

Question 46

minimum frequency of photon produced by pair annihilation

Answer 46

``` 2mc² = 2hf mc² = hf f = mc²/h ```

Question 47

why will the photons have more than the minimum energy?

Answer 47

in addiction to the rest mass the colliding particles will have kinetic energy

Question 48

why must particles travel at high speeds?

Answer 48

to overcome the coulomb force of repulsion

Question 49

why can two positrons not annihilate eachother

Answer 49

in conflict with conservation of charge