Particles

Question 1

Which part of the atom has the largest specific charge and why?

Answer 1

The electron

(It has the same magnitude of charge as the proton but a much smaller mass)

Question 2

Why do the proton, neutron and electron deflect differently in a magnetic field?

Answer 2

Neutron → 0 specific charge so zero deflection

Electron → Greatest specific charge so greatest deflection

Proton → Smaller deflection in opposite direction as specific charge smaller and opposite

Question 3

How do you calculate the specific charge of a nucleus?

Answer 3

Divide the total charge of the protons by the total mass of nucleus

(Protons + Neutrons)

Question 4

How do you calculate the specific charge of an ion?

Answer 4

Charge of the ion (Protons - Electrons) divided by total mass of ion

Question 5

What is an isotope?

Answer 5

An atom with the

1. same number of protons
2. Different number of neutrons

Question 6

When will an isotope undergo radioactive decay?

Answer 6

If the nucleus has:

1. too many or too few protons
2. Too many nucleons
3. Too much vibrational energy

Question 7

What happens in alpha (α) decay?

Answer 7

A nucleus ejects a helium nucleus (2 protons and 2 neutrons)

Decreasing its nucleon number by 4

And its proton number by 2

Question 8

What happens in Beta Minus (β^-) Decay?

Answer 8

A neutron turns into a proton

Ejecting a fast moving electron (β^-) and an anti-electron neutrino

Question 9

What happens in Beta Plus (β⁺) Decay?

Answer 9

A proton turns into a neutron

Ejecting a fast moving positron (β⁺) and an electron neutrino

Question 10

What is wrong about this Beta Decay equation?

Answer 10

The nucleon number must not change

Question 11

Why do the α, β^-, β⁺ and γ deflect differently in a magnetic field?

Answer 11

α and β⁺ → Deflect in same direction but β⁺ larger (greater specific charge)

β^- → Equal and opposite deflection to β⁺ (Equal and opposite specific charge)

γ → No deflection (no specific charge)

Question 12

What is an antiparticle?

Answer 12

A particle with the:

1. Same mass
2. But equal and opposite charge

Question 13

What happens during Annihilation?

Answer 13

A particle collides and annihilates with its correspond antiparticle

And their mass energy (E=mc²) is converted to radiation energy

Producing at least 2 gamma photons

Question 14

Why do at least 2 photons need to be created during annihilation?

Answer 14

To conserve momentum

Before annihilation p_total = 0

AFter annihilation p_total = 0 (can’t be achieved with one photon)

Question 15

What happens during pair production?

Answer 15

A gamma photon (with energy ≥ 2 × mass energy)

spontaneously creates a particle, anti-particle pair

Question 16

What condition must pair production meet?

Answer 16

The energy of the gamma photon ≥ Mass energy of the particle anti-particle pair

(Any excess energy is used a kinetic energy for the particles produced)

Question 17

How was the anti-electron neutrino discovered?

Answer 17

During Beta decay the emitted β^- had less energy than expected so another particle carried the rest of the energy

Question 18

What are the four fundamental forces and their approximate ranges?

Answer 18

1. Strong
2. Weak
3. Electromagnetic
4. Gravitational

Question 19

What does the strong force do?

What is the exchange particle of the strong force?

Answer 19

Holds nucleons together in the nucleus

• By opposing the electromagnetic repulsion of the protons
• By attracting nucleons at small distances but repelling the, at very small distances

Gluons (between quarks), or pions (between hadrons)

Question 20

Describe the nature of the strong force

Answer 20

Very repulsive over short distance (0-0.5fm)

Attractive over larger distances (0.5fm < d < 3fm)

Negligible beyond 3fm

Question 21

What does the electromagnetic force act between and what is its exchange particle?

Answer 21

Acts between all particles with charge

Exchange particle is the photon

Question 22

What does the gravitational force act between?

Answer 22

Particles or objects with mass

The exchange particle is the graviton

Question 23

What particles does the weak force act on and what does it do?

Answer 23

Acts in any interaction leptons and hadrons (lepton-lepton or lepton-hadron) causes the decay of hadrons (by changing quark structure)

The exchange particles for the weak force are w⁺, w^- & z bosons dependent on conservation of key values (QBLS) as z bosons have no charge whereas w bosons do

Question 24

What are fundamental particles that make up the standard model? (that you need to know)

Answer 24

NOTE: Each of the leptons and and quarks has an corresponding anti-lepton and anti-quark

Question 25

What is the quark structure of a proton?

Answer 25

Up, Up, Down

Question 26

What is the quark structure of a neutron?

Answer 26

Up, down, down

Question 27

How is a muon different from an electron?

Answer 27

Both are leptons, muon is much heavier than the electron, produced in cosmic ray showers

Question 28

What are hadrons?

Answer 28

**Particles that are made up of quarks**

Question 29

How are baryons and mesons different?

Answer 29

Both are hadrons (made up of quarks) But **Baryons are made up of 3 quarks** And **Mesons are made up of 1 quark 1 anti-quark**

Question 30

What are the similarities and differences between **W bosons and photons?**

Answer 30

**Both are exchange particles** But **W bosons mediate the weak force, Photons mediate electromagnetic** W bosons carry charge of +1 or -1, Photons have no charge W bosons have mass, Photons are massless

Question 31

What are the similarities and differences between gluons and pions?

Answer 31

**Both mediate the strong force** **But gluons act between quarks, Pions act between hadrons** (to keep the nucleus together) Gluons have no mass, Pions have mass

Question 32

What does the **Higgs Boson do?**

Answer 32

It **creates the Higgs field** Which **gives mass to particles**

Question 33

What quantities are **always conserved in every interaction?**

Answer 33

* **Total momentum** * **Total energy** * **Charge** * **Baryon** * **Lepton number** NOTE 1: **Kinetic energy** is conserved in **elastic collisions** NOTE 2: **Strangeness** is conserved in all interactions **apart from weak**

Question 34

What must you know about k-mesons? (kaons)

Answer 34

They are made of **1 quark and 1 anti-quark** (mesons) ## Footnote **They have non-zero strangeness** **Produced by strong interactions, Decay (into pions) by weak interactions**

Question 35

What must you know about π-mesons? (pions)

Answer 35

They are **made up of 1 quark and 1 anti-quark (mesons)** ## Footnote **They have strangeness = 0**

Question 36

What is the most stable lepton and what is the most stable hadron? (That other isolated particle will eventually decay into)

Answer 36

The **electron** and the **proton**

Question 37

Why can't this muon decay happen like this? (What's the mistake with the logic in the table?)

Answer 37

When electron and muon type particles are involved **each lepton number must be considered separately**

Question 38

What is the formula for a muon decaying into an electron?

Answer 38

Question 39

What is the feynman diagram for an electron-electron collision?

Answer 39

Question 40

What is the feynman diagram for **β^- Decay?**

Answer 40

Question 41

What is the feynman diagram for **β+ Decay?**

Answer 41

Question 42

What is the quark feynman diagram for **β^- Decay?**

Answer 42

Question 43

What is the quark feynman diagram for **β+ Decay?**

Answer 43

Question 44

Identify the unknown particles in this feynman diagram for electron capture

Answer 44

Question 45

Identify the unknown particle in this feynman diagram for the electron proton collision

Answer 45

Question 46

Identify the unknown quark in the feynman diagram for electron capture

Answer 46

Question 47

Identify the unknown exchange particle in the quark feynman diagram of electron proton collision

Answer 47

Question 48

Which particles have a baryon number = +1? Which have a B = -1? Which have a B = 0

Answer 48

**Baryons = +1** **Anti-Baryons = -1** **All other particles (including mesons) = 0**

Question 49

Which particles have a Lepton number = +1? Which have a L = -1? Which have a L = 0

Answer 49

**Leptons = +1** **Anti-Leptons = -1** **All other particles = 0**

Question 50

What is the muon lepton number of an electron?

Answer 50

0! Only muons and muon neutrinos have L_muon = +1

Question 51

What is the electron lepton number of a muon?

Answer 51

0! Only electrons and electron neutrinos have L_electron = +1

Question 52

What is the formula for electron capture?

Answer 52

^A_ZX + ⁰_-1e^-1 → ^A _Z-1Y+ v_e proton turns into a neutron _{You do not need to know this}

Question 53

What is the formula for neutron emission?

Answer 53

^A_ZX → ^A-1_ZY + ¹₀n You do not need to know this

Question 54

What is the formula for proton emission?

Answer 54

^A_ZX → ^A-1_Z-1Y+ ¹₁P You do not need to know this

Question 55

Why was the Antiproton not discovered until 1955?

Answer 55

It was only then that large enough particle accelerators were built in order to form large enough particles

Question 56

Why can't particles such as muons or leptons decay into baryons?

Answer 56

Particles can't decay into bigger particles than themselves

Question 57

Why are quarks only found in baryons and mesons?

Answer 57

Quarks cannot exist on their own

Question 58

Why did it take so long for the Higgs boson to be discovered?

Answer 58

Was not discovered until 2012 as there was not a particle accelerator big enough to form the particle until CERN

Question 59

Which exchange particles have mass?

Answer 59

W⁺, W^-, Z⁰

Question 60

Which exchange particles have charge?

Answer 60

W⁺, W^-

Question 61

What is the case at junctions of Feynman diagrams?

Answer 61

All conservation laws apply

Question 62

How are particles and exchange particles represented on Feynman diagrams?

Answer 62

Exchange particles - wiggly lines Particles - straight lines

Question 63

What is on the y-axis for feynman diagrams?

Answer 63

Time

Question 64

Which other quark can strange quarks decay into?

Answer 64

Up quarks

Question 65

Which quark is the heaviest

Answer 65

Strange quark