Particles

Question 1

Give the overall charge of an atom.

Answer 1

Neutral or zero

Question 2

Give the overall charge of a nucleus.

Answer 2

Positive

Question 3

Give the approximate size of an atom.

Answer 3

1 x 10^-10 m

Question 4

Give the approximate size of a nucleus.

Answer 4

1 x 10^-15 m

Question 5

What is found between the nucleus and electrons?

Answer 5

Empty space

Question 6

In A-Z nuclide notation, what do A and Z represent?

Answer 6

A = nucleon number

Z = proton number / atomic number

Question 7

Which number, A or Z, defines which element it is?

Answer 7

Z (proton/atomic number)

Question 8

Give the definition for nucleon number.

Answer 8

Total number of protons and neutrons.

Question 9

Complete: atoms have equal number of… and …

Answer 9

Protons and electrons.

Question 10

How do atoms become positive ions?

Answer 10

They lose electrons.

Question 11

How do atoms become negative ions?

Answer 11

They gain electrons.

Question 12

How do we work out the mass of an atom, ion or nucleus in kilograms?

Answer 12

Number of nucleons x 1.67 x 10^-27

(no need to include electrons)

Question 13

How do we work out the charge of a nucleus in coulombs?

Answer 13

Number of protons x 1.6 x 10^-19

Question 14

How do we work out the charge of an ion in coulombs?

Answer 14

Relative charge x 1.6 x 10^-19

Question 15

How do we calculate specific charge?

Answer 15

Specific charge = charge / mass = Q /m

Question 16

What are the units for specific charge?

Answer 16

C kg^-1

Question 17

What are isotopes?

Answer 17

Atoms with the same number of protons and different numbers of neutrons.

Question 18

True or false: isotopes have different chemical properties.

Answer 18

False

Question 19

True or false: isotopes have different nuclear stability.

Answer 19

True

Question 20

Describe the role of the strong nuclear force in nuclear stability.

Answer 20

Balances the electrostatic repulsion between positively charged protons.

• Holds nucleons in an equilibrium position (stops them moving further apart or closer together).

Question 21

Is the strong nuclear force associated with charge?

Answer 21

No – acts equally between protons and neutrons.

Question 22

Describe how and explain why the strength of the nuclear force varies with nuclear separation.

Answer 22

Below 0.5 fm -> repulsive –> stops nucleons collapsing into a point.

Between 0.5 – 3.0 fm -> attractive –> binds nucleons.

Beyond 3.0 fm -> zero -> prevents nucleons in different atoms being attracted.

Question 23

What type of nuclei normally undergo alpha decay?

Answer 23

Massive nuclei.

Question 24

What is an alpha particle made up of?

Answer 24

2 protons and 2 neutrons (helium nucleus)

Question 25

What type of nuclei normally undergo beta minus decay?  

Answer 25

Neutron-rich nuclei (high neutron to proton ratio). 

Question 26

What is a beta minus particle? 

Answer 26

An electron

Question 27

Describe the change in the nucleons during beta minus decay. 

Answer 27

A neutron changes into a proton. 

Question 28

Name the extra particle emitted in beta minus decay. 

Answer 28

Electron anti-neutrino 

Question 29

Why did scientists hypothesise the extra particle? 

Answer 29

- Total energy after the decay was less than the total energy before.  - Missing energy must be carried away by another particle to conserve energy. 

Question 30

Why was it difficult to detect the extra particle emitted in beta minus decay? 

Answer 30

It has no mass and no charge.

Question 31

What type of nuclei normally undergo gamma decay? 

Answer 31

Nuclei that need to lose excess energy. 

Question 32

What is a gamma ray? 

Answer 32

High energy EM wave. 

Question 33

Which decays lead to the formation of an atom of a different element? Why? 

Answer 33

- Alpha and beta minus decay.  - As the proton number changes. 

Question 34

Describe the duality of EM radiation. 

Answer 34

Can behave as a wave or a particle. 

Question 35

What is a photon? 

Answer 35

A packet or quantum of EM energy.  (Has no mass and no charge) 

Question 36

Use the data sheet to write down 2 equations for photon energy. 

Answer 36

E = hf = hc/ λ

Question 37

The energy of a photon is directly proportional to… 

Answer 37

Frequency 

Question 38

The energy of a photon is inversely proportional to… 

Answer 38

Wavelength 

Question 39

Give the definition for the electron-volt. 

Answer 39

The energy gained by an electron that is travelling through a potential difference of 1 V. 

Question 40

How do we convert eV to J? 

Answer 40

Multiply by 1.6 x 10^-19 

Question 41

How do we convert J to eV? 

Answer 41

Divide by 1.6 x 10^-19 

Question 42

Give two similarities between particles and anti-particles. 

Answer 42

Mass and rest energy 

Question 43

Give one difference between particles and anti-particles. 

Answer 43

Charge 

Question 44

What is energy-mass equivalence? 

Answer 44

- Energy can be converted into mass.  - Mass can be converted into energy.  - Calculated by E= mc² 

Question 45

What happens in pair production? 

Answer 45

A gamma photon interacts with a nucleus and the energy of the photon is used to create a particle and anti-particle pair. 

Question 46

Which pair of particles is most likely to be created during pair production? Explain why. 

Answer 46

Electron and positron as they have the lowest rest energy. 

Question 47

Why does it need to be a gamma photon for pair production? 

Answer 47

Highest energy. 

Question 48

How can we calculate the minimum energy of the photon required for pair production? 

Answer 48

E_min = 2 x rest energy of particle/anti-particle 

Question 49

How can you convert MeV into J? 

Answer 49

x 10⁶  x 1.6 x 10^-19 

Question 50

What happens in annihilation? 

Answer 50

A particle meets its equivalent antiparticle.  Their mass is converted into energy in the form of two gamma photons. 

Question 51

Why are two gamma photons produced in annihilation? 

Answer 51

They travel in opposite directions to conserve momentum. 

Question 52

How can we calculate the minimum energy of one of the photons produced in annihilation? 

Answer 52

E_min = rest energy of particle/anti-particle 

Question 53

Why is E_min = rest energy of particle/anti-particle  the minimum energy of the photon during annihilation?

Answer 53

The particle and anti-particle may have additional kinetic energy. 

Question 54

Describe the role of exchange particles in particle interactions. 

Answer 54

- Move between particles.  - Give rise to the force between them. 

Question 55

Name the four fundamental forces from strongest to weakest. 

Answer 55

- Strong nuclear force (or strong interaction)  - Electromagnetic force  - Weak nuclear force (or weak interaction)  - Gravity 

Question 56

Which of the four fundamental forces do particle physicists normally ignore? Why? 

Answer 56

Gravity as it is so weak – negligible effect. 

Question 57

Give the exchange particle for the strong nuclear force. 

Answer 57

Pions (π) 

Question 58

Give the exchange particle for the electromagnetic force. 

Answer 58

Virtual photons (ϒ) 

Question 59

Give the exchange particle for the weak nuclear force. 

Answer 59

W⁺ and W^- bosons 

Question 60

Give the particles affected by the strong nuclear force. 

Answer 60

Hadrons 

Question 61

Give the particles affected by the electromagnetic force. 

Answer 61

Charged particles 

Question 62

Give the particles affected by the weak nuclear force. 

Answer 62

All particles 

Question 63

Give the range of the electromagnetic force. 

Answer 63

Infinite 

Question 64

Give the range of the weak nuclear force. 

Answer 64

10^-18 m 

Question 65

Describe and explain the relationship between the mass of the exchange particle and the range of the force. 

Answer 65

Larger mass -> shorter range.  Requires more energy to create -> only exists for shorter time -> shorter distance. 

Question 66

Describe two differences between hadrons and leptons. 

Answer 66

- Hadrons experience the strong interaction but leptons do not.  - Hadrons are made up of quarks but leptons are fundamental. 

Question 67

Give two examples of baryons. 

Answer 67

3 quarks (or 3 anti-quarks) 

Question 68

Name the only stable baryon. 

Answer 68

Proton

Question 69

Give the baryon number of protons and neutrons. 

Answer 69

+1

Question 70

Give the baryon number of antiprotons and antineutrons. 

Answer 70

-1

Question 71

Data sheet: Give the quark combination for a proton. 

Answer 71

uud

Question 72

Data sheet: Give the quark combination for a neutron. 

Answer 72

udd

Question 73

Why do neutrons have a higher mass than protons? 

Answer 73

d quark has a higher mass than u quark 

Question 74

Give two examples of mesons. 

Answer 74

Pions and kaons 

Question 75

ive the quark structure of mesons. 

Answer 75

A quark and an antiquark 

Question 76

True or false: All mesons are unstable. 

Answer 76

True

Question 77

Name the most stable meson. Explain why. 

Answer 77

Pions –> lightest –> lowest energy. 

Question 78

Name the strange meson. Explain what strangeness tells you about quark structure. 

Answer 78

Kaons -> contain a strange or anti-strange quark. 

Question 79

How are kaons produced? 

Answer 79

By the strong interaction -> produced in pairs of strange particles. 

Question 80

How do kaons decay? 

Answer 80

By the weak interaction -> decay into pions. 

Question 81

Give the strangeness of the four kaons: K⁺, K^-, K⁰, ^_K⁰  

Answer 81

K⁺= +1    K^-= -1     K⁰= +1     ^_K⁰=-1     

Question 82

Why do kaons have a higher mass than pions? 

Answer 82

s squark has higher mass than u and d quarks 

Question 83

Why do kaons have a higher mass than pions? 

Answer 83

s squark has higher mass than u and d quarks 

Question 84

Give three examples of leptons. 

Answer 84

Electrons, muons and neutrinos 

Question 85

Compare electrons and muons. 

Answer 85

- Same charge.  - Muons are heavier than electrons.  - Electrons are stable, but muons decay into electrons. 

Question 86

Give the mass and charge of neutrinos. 

Answer 86

Zero mass and zero charge. 

Question 87

Describe the four particle interaction conservation laws. 

Answer 87

Baryon number (B) – always conserved.  Charge (Q) – always conserved.  Lepton number (L) - Le and Lµ always conserved separately.  Strangeness (S) – always conserved in strong interaction, in weak interaction changes by -1, 0 or +1. 

Question 88

State two other quantities that are conserved in all interactions. 

Answer 88

Energy and momentum. 

Question 89

Use the conservation laws to explain why strange particles are always produced in pairs. 

Answer 89

Strange particles produced by strong interaction -> strangeness must be conserved -> pair have equal and opposite strangeness to cancel to zero. 

Question 90

In which type of interaction can quark character change? 

Answer 90

Weak interaction only. 

Question 91

Work out the change of quark in beta minus decay. 

Answer 91

d -> u

Question 92

Work out the change of quark in beta plus decay. 

Answer 92

u -> d

Question 93

What is quark confinement? 

Answer 93

- Not possible for quarks to exist in isolation.  - The energy supplied to try separate a quark would cause pair production of another quark and anti-quark pair. 

Question 94

Why does particle physics research rely on the collaborative efforts of large teams of scientists and engineers? 

Answer 94

- Particle accelerators are very expensive -> collaboration helps to spread the cost.  - Many skills and disciplines required.  - Lots of data to process.  - Results of experiments must be independently peer reviewed before confirmed.