Particle Physics

Everything particle physics related

What is an exchange particle?

What is an exchange particle?

A virtual particle that lets a force act between 2 particles in an interaction.

Are strange particles more massive than u or d quarks?

Yes, resulting in the being heavier.

If the reactants combined rest energy is less than the products combined rest energy, what has occurred? (2 marks)

Kinetic energy of the reactants is greater than the kinetic energy of the products. This kinetic energy is then used in the rest energy of the products.

Why wont microwave waves not ionise neutral atoms?

Since its wavelength is very big, it has little energy.

Why would a nucleus undergo electron capture?

Because it is proton rich. It wants to convert protons to neutrons.

What is the difference between electron capture and electron-proton collisions?

In electron capture, a proton within a nucleus captures an electron from the atom, turning into a neutron and also emitting a neutrino.

In electron-proton capture, a free electron is fired at a free proton and collides with it, producing a neutron and a neutrino.

What is the exchange particle for electron capture, and what particles are produced?

W+ boson.

Neutron and an electron neutrino.

How many quarks does a meson have?

2

How many quarks does a baryon have?

3

What special property do strange particles have?

They are always produced in pairs

In what type of interaction do strange particles decay?

Weak interaction

In what type of interaction is strangeness conserved?

Strong interaction only.

What properties are always conserved in particle interactions?

Charge (Q), Baryon Number (B), Lepton Number (Le and Lu), Energy, Mass & Momentum

What is specific charge?

The specific charge of a particle is the ratio of its charge to its mass, given in Ckg-1

Describe the role of B decay in the prediction of the existence of the neutrino.

It appeared that in B decay, energy was not being conserved. The neutrino was hypothesised as a particle that had no mass (as it hadn’t been detected before) and had no charge (to conserve charge) but allowed energy to be conserved.

A proton and an antiproton are produced by a proton-proton collision. Name this process.

Pair production

An antiproton and a proton interact. Name the process and state what is produced.

Annihilation, two gamma ray photons

What is the quark combination of K+?

up, anti-strange

What is the quark combination of K-?

strange, anti-up

What is the quark combination of K0?

EITHER:

down, anti-strange

strange, anti-down

What is the quark combination of π+?

up, anti-down

What is the quark combination of π-?

down, anti-up

What is the quark combination of π0?

EITHER:

up, anti-up

down, anti-down

strange, anti-strange

What interaction creates strange particles?

Strong interaction

What interaction must strangeness be conserved?

Strong interaction

How much can strangeness change by during the weak interaction?

0,-1 or +1

State what roles exchange particles can play in an interaction

Transfers: energy, momentum, force and sometimes charge

An electron collides with a neutral atom and ionizes it. What are the particles present after the collision?

2 electrons and a positive ion

Artificial radioactive nuclides are manufactured by placing naturally-occurring nuclides in a nuclear reactor. They are made radioactive in the reactor as a consequence of bombardment by what particle?

Neutrons.

What is the specific charge of an electron?

• -1.60×10-19C

What term means 'per unit mass' when describing a physical quantity?

• Specific

What are the letters form both Nucleon Number and Proton Number?

Nucleon number: A

Proton number: Z

What is the approximate radius of a nucleus relative to the atom?

1×10-5

How are the electrons in an atom organised?

• In orbitals (shells)

Which subatomic particle has a relative atomic mass of 1/2,000?

• Electrons

What are the units of specific charge?

• C/kg

What is a nuclide?

• A nuclide refers to a specific nucleus that contains a certain number of protons and neutrons. (A nuclide is a specific isotope of an element)

Explain how radioactive carbon-14 can be used to find the age of a fossil. (3 marks)

• All living organisms have the same amount of carbon-14 atoms as a percentage of all carbon isotopes.

• Once the organism dies, it no longer absorbs carbon from the atmosphere.

• Carbon-14 is radioactive and so will decay over a known half life.

• (The older the fossil is, the fewer carbon-14 isotopes it will contain and the less radiation it emits.)

What property of fossils are determined by using carbon isotopes?

• Age

The distance at which the strong nuclear force becomes repulsive is about what?

• 0.5fm and under

When does alpha decay occur?

In very large nuclei (containing more than 82 protons)

When does Beta minus decay occur?

When a nuclei has too many neutrons.

Why was the Antineutrino hypothesised? (5 marks)

• When scientists first observed beta decay, they thought that neutrons were decaying into a proton and an electron only.

• They noticed that the energy of the neutron before the decay was larger than the energy of the proton and electron after the decay: energy was not being conserved.

• To account for this, scientists hypothesised that a new type of particle was being produced and carrying away some energy.

• This particle must have zero (or almost zero) mass and must be electrically neutral (to obey charge conservation).

• This particle was then called a neutrino but we now know it to be an antiparticle called an antineutrino.

Which subatomic particle is not affected by the strong nuclear force?

• Electrons

What would happen to a nucleus without the strong nuclear force?

• Break apart

What is meant by the AZ​X notation for atoms?

The AZ​X notation is used in decay equations to represent different isotopes of an element X

A represents the nucleon number

Z represents the proton (atomic) number

What is Molecule labelling?

• Molecule labelling uses radioactive isotopes to track mechanisms of specific molecules.

  • A regular atom is swapped out for an isotope, which behaves exactly the same due to the proton number being the same.

  • The isotope is detectable due to its differing number of neutrons.

Why might carbon dating not be so reliable in the future?

• Carbon isotope ratio is being altered by humans.

What are the products of Annihilation? (2 marks)

• A pair of gamma photons

• The energy carried aa must equal the total energy of the particles to begin with (kinetic energy + rest mass energy)

• (Each gamma photon must carry away at least the rest mass energy of one particle)

What are the products of Pair production? (2 marks)

• Particle-Antiparticle pair

• Energy of the photon with spontaneously turns into the pair must have at least the total rest mass energy of the pair it creates.

What is the weak nuclear force responsible for? (3 marks)

• The weak nuclear force is responsible for beta-plus and beta-minus decay, as well as electron capture interactions.

Which fundamental force is responsible for contact forces?

• Electromagnetic force

What is the exchange particle for the strong nuclear force?

Gluon/pion

What is the exchange particle for the electromagnetic force?

Virtual photon (called “virtual” as they only exist for a very short time)

What are the 3 exchange particles for the weak nuclear force?

• W+

• W-

• Z0

What are exchange particles sometimes also called?

• Gauge bosons

What are the two types of Hadrons?

• Baryons - containing 3 quarks. (Protons, neutrons)

• Mesons - containing 2 quarks (Pions, kaons)

Where can Mesons be found? (2 marks)

• Cosmic rays

• Particle accelerators

What are Leptons made up of?

• Nothing, they are fundamental particles (Electrons, Muons, Neutrinos)

Do Leptons feel the SNF?

NO!

What are Muons? (2 marks)

• Heavier than electrons

• Unstable and always decay into electrons

Where are Muons found? (1 mark)

• Cosmic Rays.

What are Neutrinos? (2 marks)

• Leptons that are massless with 0 charge

What are the 2 types of Lepton numbers?

• Electron lepton number (Le)

• Mon lepton number (Lu)

What is the only interaction where strangeness is conserved?

• Strong interaction (SNF)

What interaction are strange particles produced and what interaction decays them?

• Strong interaction produces strange particles (Kaons are always produced in pairs)

• Weak interaction decays strange particles (Strangeness can change by -1,0 or +1 only)

What type of number are lepton and baryon numbers? (1 mark)

• Quantum numbers

Which photons have the most energy? (1 mark)

• Gamma

What kind of photon is produced in annihilation? (1 mark)

• Gamma

Can exchange particles both push particles together & pull particles apart?

Yes.

What is the antiparticle for π⁰

π⁰

^(itself)

What mesons contain strange quarks?

ONLY Kaons.

How can quarks change type?

• Through the weak nuclear force

How many quarks can change at one time in a weak interaction?

• 1 quark

Why do scientists need to work collaboratively in particle physics? (3 marks)

• Particle physics experiments create massive amounts of data.

• Particle physics experiments are also very expensive to run.

• Large teams working collaboratively are needed to validate new knowledge in particle physics.

Why is an anti-electron neutrino produced in beta-minus decay?

• In order for Lepton number to be conserved.

e- = Le = 1

Anti electron neutrino = Le -1

As we had no leptons at the start, now lepton number is balanced

Why is a neutrino produced in beta-plus decay?

• In order to conserver Lepton number.

A positron is produced (Lepton number -1)

An electron neutrino is also produced (Lepton number +1)

Therefore Lepton number is conserved.

What particle is NOT affected by the weak interaction? (1 mark)

• Photon

Is the electron neutrino a fundamental particle?

Yes.

Is the energy of a photon directly proportional to the frequency of the radiation?

Yes

What photons have the highest frequency?

• Gamma photon

Which photons have the lowest frequency?

• Radio photons

Why are Kaons always produced in pairs?

• Kaons are produced via the strong interaction

• Strangeness is conserved in the strong interaction

• Therefore, kaons must be produced in pairs to cancel out the strangeness value (-1 +1 =0)

Can forces act instantaneously?

No

What is the exchange particle of the strong nuclear force between quarks?

Pion/Gluon

What is the only interaction that can change quarks “flavour”?

• Weak interaction

What are the two types of lepton numbers that need to be conserved separately?

• Lepton electron number

• Lepton muon number

What is the electron lepton number of a muon antineutrino?

• 0

What is the difference between strong force and weak force?

• Strong force occurs when hadrons interact

• Weak force occurs when a quark changes, and there is a decay

What is the photon theory of light?

• One photon emits one electron if the photon is above the threshold frequency.

What property defines a hadron?

• Experiences the strong nuclear force

Explain the process of pair production. (3 marks)

• Proton interacts with electrons/nucleus

• Energy of photon used to create particle antiparticle pair

• To conserve momentum, photon needs to interact with interacting particle.

How can you work out the quark composition of mesons?

• Charge for a start needs to add up

• Mesons are a quark antiquark pair

• Pions do NOT contain strangeness (except for pi 0)

• Kaons have to contain strangeness

What are exchange particles?

• Acts as a force carrier between the particles.

What do kaons decay into and by what interaction?

• Pions

• Weak interaction with the W+ boson.

What do muons decay into?

• Electrons

Through what interactions are strange particles created and then decayed?

• Created via the strong interaction

• Decayed by the weak interaction.

Do quarks have baryon numbers?

• Yes

What is the baryon number for all types of normal quarks?

• + 1/3

What is the baryon number for all types of antiquarks?

• - 1/3