Topic 1: Particles - Quiz Review

What are the relative masses of a proton, neutron, and electron?

Proton: $1$, neutron: $1$, electron: $\frac{1}{2000}$ (or negligible).

What are the relative charges of a proton, neutron, and electron?

Proton: $+1$, neutron: $0$, electron: $-1$.

What is the overall charge of an atom?

Neutral or zero.

What is the overall charge of a nucleus?

Positive.

What is the approximate size of an atom?

$1 \times 10^{-10}\,m$.

What is the approximate size of a nucleus?

$1 \times 10^{-15}\,m$.

What is found between the nucleus and the electrons in an atom?

Empty space.

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

$A$ represents the nucleon number, and $Z$ represents the proton number (or atomic number).

Which number, $A$ or $Z$, defines which element an atom is?

$Z$ (the proton number / atomic number).

What is the definition of nucleon number?

The total number of protons and neutrons.

A neutral atom has equal numbers of which two particles?

Protons and electrons.

How do atoms become positive ions?

They lose electrons.

How do atoms become negative ions?

They gain electrons.

What is the magnitude of the charge on an electron or proton?

$1.60 \times 10^{-19}\,C$.

What is the mass of a nucleon?

$1.67 \times 10^{-27}\,kg$.

What is the mass of an electron?

$9.11 \times 10^{-31}\,kg$.

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

$\text{Number of nucleons} \times 1.67 \times 10^{-27}\,kg$ (no need to include electrons).

How do we calculate the charge of a nucleus in coulombs?

$\text{Number of protons} \times 1.60 \times 10^{-19}\,C$.

How do we calculate the charge of an ion in coulombs?

$\text{Relative charge} \times 1.60 \times 10^{-19}\,C$.

How is specific charge calculated?

$\text{Specific charge} = \frac{\text{charge}}{\text{mass}} = \frac{Q}{m}$.

What are the units for specific charge?

$C\,kg^{-1}$.

What are isotopes?

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

True or false: Isotopes have different chemical properties.

False.

True or false: Isotopes have different nuclear stability.

True.

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

It balances the electrostatic repulsion between positively charged protons and holds nucleons in an equilibrium position (stopping them from moving further apart or closer together).

Is the strong nuclear force associated with charge?

No - it acts equally between protons and neutrons.

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

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.

What type of nuclei normally undergo alpha decay?

Massive nuclei.

What is an alpha particle made up of?

$2$ protons and $2$ neutrons (a helium nucleus).

What is the general alpha decay equation?

$^A_Z X \rightarrow ^{A-4}_{Z-2}Y + ^4_2\alpha$.

What type of nuclei normally undergo beta minus ($\beta^-$) decay?

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

What is a beta minus particle?

An electron.

Describe the change in the nucleons during beta minus decay.

A neutron changes into a proton.

Name the extra particle emitted in beta minus decay.

Electron anti-neutrino.

Why did scientists hypothesise the existence of the electron anti-neutrino in beta minus decay?

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

Why was it difficult to detect the electron anti-neutrino?

It has no mass and no charge.

What is the general beta minus decay equation?

$^A_Z X \rightarrow ^A_{Z+1}Y + ^0_{-1}e^- + \bar{\nu}_e$.

What type of nuclei normally undergo gamma decay?

Nuclei that need to lose excess energy.

What is a gamma ray?

High energy EM wave.

Which radioactive decays lead to the formation of an atom of a different element, and why?

Alpha and beta minus decay, because the proton number changes.

Describe what is meant by the duality of EM radiation.

It can behave as a wave or a particle.

What is a photon?

A discrete packet/quantum of EM energy (has no mass and no charge).

What are the two equations used to calculate photon energy?

$E = hf = \frac{hc}{\lambda}$.

What units do these equations calculate energy in?

Joules

The energy of a photon is directly proportional to…

Frequency

The energy of a photon is inversely proportional to…

Wavelength

Give the definition for the electron-volt.

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

How do we convert eV to J?

Multiply by 1.6 x 10^-19

How do we convert J to eV?

Divide by 1.6 x 10-19

Give two similarities between particles and anti-particles.

Rest mass and rest energy

Give one difference between particles and anti-particles.

Charge

What is energy-mass equivalence?

- Energy can be converted into mass.

- Mass can be converted into energy.

- Calculated by E= mc^2

What happens in pair production?

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

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

Electron and positron as they have the lowest rest energy.

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

Highest energy

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

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

Use the data sheet to write down the rest energy of an electron/positron.

0.510999 MeV

How can you convert MeV into J?

x 10^6 x 1.6 x 10^-19

What happens in annihilation?

A particle meets its equivalent antiparticle.

Their mass is converted into energy in the form of two gamma photons.

Why are two gamma photons produced in annihilation?

They travel in opposite directions to conserve momentum.

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

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

Why is this the minimum energy of the photon?

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

Describe the role of exchange particles in particle interactions.

- Move between particles and transfer momentum.

- Due to conservation of momentum this produces a force between them.

Name the four fundamental forces from strongest to weakest.

- Strong nuclear force (or strong interaction)

- Electromagnetic force

- Weak nuclear force (or weak interaction)

- Gravity

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

Gravity as it is so weak – negligible effect.

Give the exchange particle for the strong nuclear force.

Pions (π)

Give the exchange particle for the electromagnetic force.

Virtual photons (ϒ)

Give the exchange particle for the weak nuclear force.

W+ and W- bosons

Give the particles affected by the strong nuclear force.

Hadrons

Give the particles affected by the electromagnetic force.

Charged particles

Give the particles affected by the weak nuclear force.

All particles

Give the range of the strong nuclear force.

10^-15 m

Give the range of the electromagnetic force.

Infinite

Give the range of the weak nuclear force.

10^-18 m

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

Larger mass -> shorter range.

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

Draw a Feynmann diagram for the electromagnetic repulsion between two electrons.

Draw a Feynmann diagram for beta minus decay.

Draw a Feynmann diagram for beta plus decay.

Draw a Feynmann diagram for electron capture.

Draw a Feynmann diagram for electron-proton collision.

Draw a simple family tree for particle classification.

Describe two differences between hadrons and leptons.

- Hadrons experience the strong interaction but leptons do not.

- Hadrons are made up of quarks but leptons are fundamental.

Give two examples of baryons.

Protons and neutrons.

Give the quark structure of baryons.

3 quarks

Name the only stable baryon.

Proton

Give the baryon number of protons and neutrons.

+1

Give the baryon number of antiprotons and antineutrons.

-1

Data sheet: Give the quark combination for a proton.

uud

Data sheet: Give the quark combination for a neutron.

udd

Why do neutrons have a higher mass than protons?

d quark has a higher mass than u quark

Give two examples of mesons.

Pions and kaons

Give the quark structure of mesons.

A quark and an antiquark

True or false: All mesons are unstable.

True

Name the most stable meson. Explain why.

Pions –> lightest –> lowest energy.

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

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

How are kaons produced?

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

How do kaons decay?

By the weak interaction -> decay into pions.

Data sheet: Give the quark combinations for: π+, π0 and π-

π+= ud̅ π0 = uu̅ or dd̅ π- = u̅d

Give the strangeness of the four kaons: K+, K-, K0, 𝐾0̅

K+= +1 K-= -1 K0= +1 𝐾0̅= -1

Why do kaons have a higher mass than pions?

s squark has higher mass than u and d quarks