Physics - Particles

specific charge

Q/m
a particle’s charge to mass ratio

isotope

atoms of the same element with the same number of protons

use of carbon-14

it is radioactive to we use it to find the age of organic matter through carbon dating - calculate the % of C-14 remaining in an object and use the half life to therefore calculate age

strong nuclear force (SNF)

keeps nuclei stable by counteracting electrostatic repulsion

attraction and repulsion of SNF

repulsive up to 0.5fm
attractive from 0.5fm to 3fm
after 10fm, force becomes zero

unstable nuclei

have either too many protons or neutrons so SNF can’t keep them stable, therefore they decay to become more stable

alpha decay

large nuclei with too many protons and neutrons

beta-minus decay

occurs in neutron-rich nuclei

discovery of the antineutrino

at first scientists through beta minus decay only emitted an electron but observations of the energy of the beta particle emitted showed variation therefore another particle had to be emitted. Beta particles had a range of kinetic energies so another particle was emitted to conserve energy

antiparticles

every particle has an antiparticle of the same rest energy and mass but all other properties are opposite

pair production

a photon interacts with a nucleus/atom, creating a photon and it’s antiparticle

the minimum energy of the photon, hf_min = 2E_o (rest energy)

annihilation

when matter and antimatter meet, their mass is converted into 2 photons

the minimum energy of each photon, hf_min = E_o (rest energy)

uses of annihilation

PET scanners use positron emitting isotopes inside the patient that annihilate existing electrons, emitting gamma photons that can be easily detected

electromagnetic radiation

travels in packets called photons

E = hf = hc/λ

EM radiation emittance

emitted when electrons move shells, slow down, stop or change direction

laser beams

photons of the same frequency

power of beam = no. photons passing a point per second x f

four fundamental forces

gravity, electromagnetic, weak nuclear and strong nuclear

cause of fundamental force

exchange particles / bosons

strong nuclear interaction

• exchange particle: gluon (between quarks) or pion (between nucleons)

• relative strength: 1

• range: 3×10^-15m

  • acts on: hadrons

weak nuclear interaction

• exchange particle: W boson - W⁺, W^- , W^o

• relative strength: 10^-5

• range: 10^-18 m

• rest mass: 81, 81, 93

• acts on: all particles

electromagnetic interaction

• exchange particle: virtual photon

• relative strength: 10^-2

• range: infinite

• acts on: charged particles

gravitational interaction

• exchange particle: graviton

• relative strength: 10^-38

• range: infinite

• acts on: particles with mass

electron capture

electron-proton collision

neutron-neutrino collision

proton-antineutrino collision

beta plus decay

beta minus decay

leptons

e.g. electrons, muon neutrino

fundamental so don’t experience strong interaction as have no quarks