Particles and interactions AYr1

Specific charge definition

the charge to mass ratio of a particle

Specific charge equation and units

charge/mass = Ckg^-1

nucleons definition

particles in the nucleus of an atom e.g. protons and neutrons

isotopes definition

an element with the same number of protons and electrons but different number of neutrons

SNF range attractive

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SNF range repulsive

0.5-3fm (femto metres)

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0-0.5fm

Strong nuclear force (SNF)

• Fundamental force that binds nucleons together

• counteracts electrostatic force of repulsion (between protons)

• Strongest of the fundamental forces

• Has both repulsive and attractive range to stop the nucleus collapsing in on itself

• Strangeness completely conserved

Beta minus decay equation

n → p + β⁻ + ν_e/

Alpha decay equation

Alpha particles are made of two protons and two neutrons. So 4 is nucleon number, 2 is proton number.

Antiparticle definition

A particle that has the same mass and rest energy of another particle, but all other properties are opposite (like charge) e.g:

• proton and antiproton

• electron and positron

• neutron and antineutron

Photons

packets of electromagnetic energy

Annihilation

When a particle and antiparticle collide converting all of their mass into energy in the form of two photons

Equation for annihilation

E = mc² where c is the speed of light in vacuo

Pair production

• Where a single photon is converted into an equal amount of matter and antimatter.

• The energy of the photon has to be greater than the total rest energy of the particle and antiparticle

• The excess energy is converted into kinetic energy

Fundamental forces (in order of strength)

• Strong nuclear force

• Weak nuclear force

• Electromagnetic force

• Gravity

Exchange particle

• Also known as a virtual particle

• Transmits the fundamental forces that hold nucleons, nuclei and atoms together

• size of the exchange particles determines the range of the force

Exchange particle for (in spec only):

• SNF

• WNF

• Electromagnetic (EMG)

• Gravity

• Pion (SNF)

• W+ and W- (WNF)

• Photon (EMG)

• Graviton

Weak nuclear force (WNF)

• Fundamental force that acts on all particles

• Small range (10^-18)

• Responsible for beta radiation (decay of neutrons into protons and electrons)

• Responsible for nuclear fusion

• strangeness conserved within +- 1

Electromagentic force

• holds atoms together

• Acts between all charged particles

• Infinite range

• Strength of interaction decreases with distance

• Can be attractive or repulsive

Gravity

• Weakest of the fundamental forces

• Infinite range

• Negligible on the atomic and nuclear scale

What are pions?

Exchange particles of the strong nuclear force

What is a kaon?

A particle decays into (only) pions

What is the quark structure of a K⁰ ?

K⁺?

K^–?

• down, anti-strange OR anti-down, strange

• up, anti-strange

• anti-up, strange

What is the quark structure of a π⁺?

π^–?

π⁰?

• up, anti-down

• anti-up, down

• up, anti-up OR down, anti-down

How are strange particles produced?

Produced through the strong interaction, they are always created in pairs

How do strange particles decay?

Weak interaction (e.g. kaons)

What is the only stable (free) baryon?

The proton is the only stable baryon into which other baryons eventually decay

What interactions do Hadrons decay by?

Strong, weak and electromagnetic. Leptons only decay by weak (and electromagnetic?).

Draw electron capture diagram and explain it.