Particles - AQA A Level Physics

Nucleon

A proton or a neutron in the nucleus

Nucleon number/mass number

The total number of protons and neutrons in an atom.

Proton number/atomic number

The total number of protons in an atom

Specific charge

The ratio of charge to unit mass of a particle

Strong nuclear force

The force that holds the nucleus together by countering the electrostatic force of repulsion between the protons.

Range of strong nuclear force

• Attractive from 3-4fm down

• Repulsive below 0.5fm

Unstable nuclei

Nuclei with either too many protons, neutrons or both causing the SNF to not be able to counter the electrostatic repulsion.

Alpha decay equation (A/Z X →)

A-4/ Z-2 Y + 4/2 He

Beta minus decay equation (1/0 n →)

1/1 p + 0/-1 β + ̅ν_e

Beta plus decay equation (A/Z X →)

A/Z-1 Y + 0/+1 n + 0/+1 β + ν

Beta minus decay

A neutron in the unstable nucleus transforms into a proton, emitting an electron and an electron antineutrino.

Beta plus decay

A proton in the unstable nucleus transforms into a neutron, emitting a positron and an electron neutrino.

Gamma decay

Emission of a high energy gamma ray photon.

What does gamma decay usually accompany and why?

Alpha and beta radiation in order to “de-excite” the daughter nucleus.

Electromagnetic Waves

Electric and magnetic waves that oscillate at right angles to each other.

Photons

Packets that EM waves travel in.

Planck’s equation (photon energy = )

planck’s constant (h) * frequency (f)

What did Dirac propose about antiparticles? (3)

• They have the same rest mass as their particle equivalent

• They have the opposite charge of their particle equivalent

• They will annihilate when they meet their particle equivalent

Antiparticle

Subatomic particle with the same rest mass as it’s matter counterpart but with the opposite charge.

Pair production

The process in which a photon converts into a particle-antiparticle pair.

Annihalation

The process in which a particle and it’s corresponding antiparticle meet and their total mass is converted into energy, typically in the form of 2 photons.

What is the minimum energy of the photon in pair production equal to?

The total rest mass of the particle-antiparticle pair.

What does extra energy become in pair production?

Kinetic energy in the particles

Four fundamental forces

• Strong force

• Weak force

• Electromagnetic force

• Gravitation

weak nuclear force

The force responsible for beta decay, which transforms one type of subatomic particle into another by changing their quark types and charges.

W boson

Carrier of the weak nuclear force. W bosons have non-zero rest mass and can be positive or negative.

Electron capture

A proton in a nucleus captures an inner-shell electron, transforming the proton into a neutron and emitting an electron neutrino. Involves W⁺ boson.

Electron-proton collision

An electron collides with a free proton at high speed, transforming the proton into a neutron and emitting an electron neutrino. Involves W^- boson.

Cosmic rays

High energy particles that travel through space from stars.

What happens when cosmic rays enter the atmosphere?

A shower of other short-lived particles and antiparticles is created.

Hadron

Particles/antiparticle that can interact through the strong interaction.

Lepton

Particles/antiparticle that cannot interact through the strong interaction.

Baryon

Hadron consisting of 3 quarks.

Meson

Hadron consisting of a quark and an antiquark.

Quark

What makes up hadrons.

Electron volt

(=1.6×10^-19J) Work done when an electron is moved through a p.d. of 1V.

Exchange particles

Virtual particles that mediate the fundamental forces.

Pion quark structure (+, -, 0)

u/anti d, d/anti u or u/ anti u or d/ anti d

Kaon quark structure (+)

u/anti s, s/ anti u, d/anti s or s/anti d

proton quark structure

uud

neutron quark structure

udd

Beta minus decay in terms of quarks

One of the down quarks in the neutron transforms into an up quark, forming a proton.

Beta plus decay in terms of quarks

One of the up quarks in the proton transforms into a down quark, forming a neutron.

What is conserved in particle interactions? (6)

• Energy

• Mass

• Charge

• Lepton number

• Strangeness number

• Baryon number