Particle Physics

Question 1

Conservation in a nuclear reaction

Answer 1

In a nuclear reaction,

• Mass-energy is conserved;
• Momentum is conserved;
• Electric charge is conserved

Question 2

Disintegration energy

Answer 2

When radioactive disintegration happens randomly, disintegration energy is released, Q

Question 3

Neutrino

Answer 3

• When studying the decay of β–particles, Austrian physicist Wolfgang Pauli noted that the energy and momentum were not conserved
• He proposed that a third particle, the neutrino (v) was formed

Question 4

Cockcroft and Walton

Answer 4

• Cockcroft (English) and Walton (Irish) performed first splitting of a nucleus by artificially accelerated particles
• Bombarded Lithium with artificially accelerated protons
• first artificial splitting of a nucleus
• first transmutation (changing the nucleus of one atom into the nucleus of another) using artificially accelerated particles

Question 5

Cockcroft and Walton (how)

Answer 5

-Used transformers, rectifiers and capacitors to make high dc voltage
-Voltage accelerated protons
-Protons injected from Hydrogen discharge tube into the acceleration tube
-Protons strike the Lithium at 45 degree angle
Products (Helium nuclei, α-particles) emitted at right angles
-Strike Zinc sulphide screens (scintillations seen)

Question 6

Cockcrot and Walton - energy

Answer 6

• Incident proton had energy of about 1 MeV
• Kinetic energies of Helium nuclei was 17 MeV
• There is a gain of energy in the experiment
• came from the loss of mass
• first experimental verification of Einstein’s equation E=mc2, earning Cockcroft and Walton the Nobel Prize in Physics in 1951

Question 7

Particle Accelerators

Answer 7

• When high energy particles collided, some of this energy is converted into matter
• In order to accelerate particles to required high energies, special particle accelerators needed
• The cyclotron developed
• The first circular particle accelerator
• Magnetic fields are used control the particle beams
• Electric fields are used to accelerate

Question 8

Particle accelerators - magnetic fields and electric fields

Answer 8

• Magnetic fields are used control the particle beams

- Electric fields are used to accelerate

Question 9

CERN

Answer 9

• an underground circular particle accelerator in Switzerland
• Smaller accelerator has a circumference of 7km
• Larger accelerator has a circumference of 27km

Question 10

Particle accelerators - discovery

Answer 10

• Circular particle accelerators improved as time went on
• Discovered collision of high energy protons resulted in many new particles being formed
• The higher the energy made available by better particle accelerators, the greater the mass and variety of the new particles

p + p + energy -> p + p + additional particles

Question 11

Building blocks of nature - Greeks

Answer 11

Earth, fire, wind, water

Question 12

Building blocks of nature - 1932

Answer 12

proton, neutron, electron

Question 13

Building blocks of nature - 1932 onwards

Answer 13

particle accelerators, CERN

Question 14

the positron

Answer 14

American Carl David -Anderson discovered there is a particle which is just like the electron, but of opposite charge, the positron
-Has same mass, and charge size
-Known as the antiparticle of the electron
e+ Positrons, e- electrons
-Won the Nobel prize in 1936

Question 15

Pair Production - definition

Answer 15

• The creating of two particles from energy

- An example of the conversion of energy into matter

Question 16

Pair production formula

Answer 16

hf = 2mc² + Eₖ₁ + Eₖ₂

Question 17

Pair Production - what are produced

Answer 17

-A particle and it’s antiparticle are produced

Question 18

Pair Production - what are conserved

Answer 18

-Momentum and electric charge are conserved

Question 19

Pair Production - when it occurs

Answer 19

-Occurs when high energy γ–ray photon loses its energy (hf) when it collides with a nucleus

Question 20

antiparticle

Answer 20

• Each particle has an antiparticle, denoted with the same letter with a bar over it
• E.g. nuetrino is v, then antineutrino as v

Question 21

antiparticle research

Answer 21

• English physicist Paul Dirac predicted the existence of antiparticles in the 1920’s
• Confirmed in 1955
• Physicists in CERN made antihydrogen atoms in 1995

Question 22

pair annihilation

Answer 22

-A particle and its antiparticle that are almost at rest and close to each other will come together and be destroyed, or annihilated

Question 23

Pair annihilation (Effects)

Answer 23

-Matter disappears
Energy is produced
-Momentum before and after is zero
-Two photons of equal energy moving in opposite directions are produced

Question 24

Pair annihilation formula

Answer 24

e+ + e- -> 2hf (gamma rays)

Question 25

Fundamental forces of nature

Answer 25

- strong nuclear - electromagnetic - weak nuclear - gravitational

Question 26

Strong nuclear - relative strength - acts on - occurrence - range

Answer 26

- relative strength: 1 - acts on: protons, neutrons - occurrence: binds nucleus - range: short (10⁻¹⁵ m)

Question 27

Electromagnetic - relative strength - acts on - occurrence - range

Answer 27

- relative strength: 10⁻² - acts on: charged particles - occurrence: binds atoms and molecules - range: infinite (inverse square law)

Question 28

Weak nuclear - relative strength - acts on - occurrence - range

Answer 28

- relative strength: 10⁻⁷ - acts on: all particles - occurrence: β-decay - range: short range (10⁻¹⁸ m)

Question 29

Gravitational - relative strength - acts on - occurrence - range

Answer 29

- relative strength: 10⁻³⁸ - acts on: all particles - occurrence: keeps universe together - range: infinite (inverse square law)

Question 30

mass of particles

Answer 30

- The higher the energy of the colliding particles, the greater the variety of new particles produced - Mass of particles comes from the energy of the reactions m = E/c² - Wide variety of particles became known as “Particle Zoo” as there seemed to be no relationship between them

Question 31

classification of particles

Answer 31

- Particles are classified according to whether they felt strong or weak forces - Two families emerged: - Leptons - Hadrons

Question 32

Leptons - what they are affected by

Answer 32

Affected by weak forces, and unaffected by strong ones

Question 33

Hadrons - what they are affected by

Answer 33

Affected by both strong and weak forces

Question 34

Leptons

Answer 34

- A particle that does not feel a strong force - Considered to be elementary particles -At present, 6 leptons and their antiparticles are known

Question 35

Elementary particles

Answer 35

Elementary particles are particles that have no other particles inside them or subparts to them (indivisible)

Question 36

Lepton particles

Answer 36

1. Electron 2. (Electron) Neutrino 3. Muon 4. (Muon) Neutrino 5. Tau 6. (Tau) Neutrino

Question 37

Lepton particles table

Answer 37

in ppt

Question 38

Hadrons

Answer 38

- A particle that feels the strong force - Over 100 types of hadrons known - Can be divided into two families: - Baryons - Mesons

Question 39

Baryons

Answer 39

(Greek for heavy) Masses greater than or equal to protons

Question 40

Mesons

Answer 40

have masses between electrons and protons

Question 41

Baryons particles

Answer 41

- Proton - Neutron - Lambda - Sigma

Question 42

baryons and mesons table

Answer 42

on ppt

Question 43

Mesons particles

Answer 43

- Pion | - Kaon

Question 44

Quarks

Answer 44

Quarks are elementary particles out of which baryons and mesons are made

Question 45

Known quarks

Answer 45

- There are six known quarks and their antiquarks: - Up (u) - down (d) - strange (s) - charmed (c) - top (t) - bottom (b)

Question 46

Quarks charge

Answer 46

Have a charge of either plus or minus 1/3e or 2/3e

Question 47

quarks table

Answer 47

on ppt

Question 48

Quarks history

Answer 48

- Name first used by Gell-Mann | - James Joyce came up with it in Finnegan’s Wake “Three quarks for Muster Mark!”

Question 49

What they are made up of: Mesons

Answer 49

Made up of any one quark and any one antiquark

Question 50

What they are made up of: Baryons

Answer 50

Made up of any three quarks

Question 51

What they are made up of: Antibaryon

Answer 51

Made up of any three antiquarks

Question 52

identifying a particle given the quarsk

Answer 52

p378 on book