Particle Physics

Give the relative mass of a proton, neutron and electron

P = 1

N = 1

E =Negligble

Give the relative charge of a proton, neutron and electron

P = +1

N = 0

E = -1

State the overall charge of an atom and why?

Neutral because atoms have an equal number of protons and electrons.

State the overall charge of a nucleus and why?

Positive as protons have a +1 charge and neutrons have no charge.

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

A is the nucleon number

Z is the proton/ atomic number

Give the definition of the nucleon number

The total number of protons and neutrons

How is the mass of an atom, ion, or nucleus worked out?

Number of nucleons x 1.67×10^ 27

How do we work out the charge of a nucleus?

Number of protons x 1.60×10 ^ -19

How do we calculate the charge of an ion?

Relative charge of ion x 1.60×10 ^ -19

How do we calculate specific charge?

Specific charge = charge/ mass

What are isotopes?

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

Describe the role of the strong nuclear force (SNF) in nuclear stability

Balances out the electromagnetic repulsion between positively charged protons.

Holds nucleons in an equilibrium position - stopping them from moving further apart or closer together.

Is the SNF associated with charge?

No, it acts equally between protons and neutrons

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

Below 0.5fm the force is repulsive to stop nucleons from collapsing into a point.

Between 0.5fm and 3.0fm the force is attractive to bind the nucleons together and balance the electromagnetic repulsion between protons

After 3.0fm the force is zero which prevents nucleons from different atoms being attractive.

What type of nuclei undergo alpha decay?

Large unstable nuclei

What is an alpha particle made up of?

A Helium nucleus (2 protons, 2 neutrons)

Write a general equation for alpha decay

A A - 4 4

X —>. Y + a

Z. Z - 2. 2

What type of nuclei undergo beta minus decay?

Neuton rich nuceli, too many neutrons to protons

What is the beta minus decay particle?

An electron (e-)

Describe the change during beta minus decay

A neutron changes to a proton

What exchange particle is emitted?

Electron anti-neutrino

What type of nuclei normally undergo beta plus decay?

Proton rich nuclei (too many protons to neutrons)

What is a beta plus particle?

A positron (e+)

Describe the change in the nucleus for beta plus decay

A proton changes to a nucleus

What exchange particle is emitted?

Electron neutrino

What type of nuclei undergo gamma decay?

Nuclei in an excited state that have excess energy they need to lose

What is a gamma ray?

A high speed electromagnetic wave

Which decay leads to the formation of an atom of a different element?

Alpha and beta minus decay, as the proton number changes

How did scientists hypothesise the existence of exchange particles?

Beta minus particles emitted with a continuous range of energies up to a maximum.

Total energy after the decay seemed less than the energy before.

Missing energy must be carried away by another particle to conserve energy.

Why was it difficult to detect the extra particle?

It has no mass nor charge.

Describe what is meant by the duality of EM radiation

Can behave as a wave or particle

What is a photon and what is the mass and charge of a photon?

A discrete packet or quantum of electromagnetic energy.

It has no mass nor charge.

What are the two equations for photon energy?

E = hf

E = hc/ lander

The energy of a photon is directly proportional to…

Frequency

The energy of a photon is inversely proportional to…

Wavelength

Define an electron volt

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

How do you convert from eV to J and J to eV?

EV to J = x1.6×10 ^ -19

J to eV = /1.6×10 ^ -19

What is the same between particles and anti particles?

Rest energy and rest mass

What’s 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 using E =mc²

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 particles are most likely to be created and why?

Electron and positron as they have the lowest rest energy.

Why does gamma need to be present for pair production?

It has the highest energy

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

E(min) =2x rest energy of particle/anti particle

How can you convert MeV into J?

X1.6 × 10 ^-13

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?

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 E(min) = 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

They move between particles and transfer momentum.

Due to the conservation of momentum this gives rise to a force between the particles.

Name the 4 fundamental forces from strongest to weakest.

SNF/ strong interaction

Electromagnetic force

WNF/ weak interaction

Gravity

Give the exchange particle for each fundamental force

SNF = pions

EM force = Virtual photons

WNF = W+ and W- bosons

Give the particles affected by each fundamental forces

SNF = Hadrons

EM force = Charged particles

WNF = All particles

What are the ranges of each fundamental forces?

SNF = 10 ^ -15 m

Em force = infinite

WNF = 10 ^ -18 m

Describe and explain the relationship between mass of the exchange particles and the range of the force

Large mass = shorter range

Because it requires more energy to create so only exists for a shorter time and travels a shorter distance

What is the graph of electromagnetic repulsion?

What is the graph of beta minus decay/ decay of a free neutron?

What is the graph for beta plus decay?

Define electron capture

When a proton in the nucleus captures an inner shell electron

What is the graph for electron capture?

Define electron-proton collision

When a free electron and free proton collide

What is the graph for electron-proton collision?

How are particles classified?

Particles are either Hadrons or Leptons

Hadrons can either be Baryons or Mesons

Give 2 differences between Hadrons and Leptons

Hadrons experience strong interaction, Leptons do not.

Hadrons are made up of quarks, Leptons are fundamental

What particles are Baryons?

Protons and Neutrons

What is the quark structure of Baryons?

3 quarks

What Baryon is stable?

Proton

Give the Baryon number of protons and neutrons, and the Baryon number of antiprotons and antineutrinos

Protons and Neutrons = +1

Antiprotons and Antineutrinos = -1

What is the quark structure of a proton?

UUD

What is the quark structure of a neutron?

UDD

Why do neutrons have a higher mass than protons?

A down quark has a higher mass than an up quark

What particles are Mesons?

Pions and Kaons

What is the quark structure of Mesons?

Mesons are made up of a quark and antiquark

Which Meson is stable and why?

No Mesons are stable.

However, Pions are the most stable Meson because they are light, so they have lower energy.

What Meson is strange?

Kaons, they contain one strange or anti strange quark

How are Kaons produced?

By the strong interaction, they are produced in pairs of strange particles.

How do Kaons decay?

They decay by the weak interaction into pions.

Give the quark combinations for Pions

Pion+ = up and anti down

Pion0 = up and anti up or down and anti down

Pion- = anti up and down

Give the strangeness of the four Kaons

K+ = +1 strangeness

K- = -1 strangeness

K0 = +1 Strangeness

Anti K + = -1 strangeness

Give the quark combinations of the 4 Kaons

K+ = up and anti strange

K- = strange and anti up

K0 = down and anti strange

Anti K0 = anti down and strange

Why do Kaons have a higher mass than Pions?

Strange quarks have a higher mass than up and down quarks

What are the three Leptons?

Electrons, Muons, and Neutrinos

Compare Electrons and Muons

Same charge, but Muons are heavier.

Electrons are stable, so Muons decay into Electrons

What is the mass an charge of neutrinos?

0 mass and 0 charge

What is the Lepton Electron and Lepton Muon number of each Lepton?

Lepton Electron +1 = Electrons and Electron neutrinos

Lepton Electron -1 = Positron and Anti electron neutrino

Lepton Muon +1 = Muons and muon neutrinos

Lepton Muon -1 = Anti muons and Anti muon neutrinos

What are the 4 particle conservation laws?

Baryon number = always conserved

Charge = always conserved

Lepton number = Lepton Electron and Lepton Muon number is always conserved

Strangeness = always conserved in the strong interactions, but in weak interaction it can change by +1, -1 or 0

What other quantities are always conserved?

Energy and momentum

Which conservation laws explain why strange particles are produced in pairs?

Strange particles produced by the strong interactions, mean that strangeness must be conserved

So, the pair must have equal and opposite strangeness so they cancel out to zero.

In which interaction can quark structure change?

ONLY in weak interaction

What is the quark change in beta plus and beta minus decay?

BETA MINUS = down quark to up quark

BETA PLUS = up quark to down quark

Define quark confinement

It is not possible for quarks to exist in isolation.

This is because the energy needed to try separate a quark would cause pair production, resulting in another quark and anti quark pair being produced.

Why does particle physics research require collaborative efforts from international teams?

Particle accelerators are very expensive, so collaboration helps to spread the cost.

Many skills and disciplines are required.

There is lots of data to process so it takes a lot of time.