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3.2 Particles and radiation - Coggle Diagram
3.2 Particles and radiation
3.2.1.1 constituents of the atom
an atom is formed of protons, neutrons and electrons
Specific Charge = charge/mass
the specific charge of a particle is the charge-mass ratio
isotopes are atoms with the same number of protons but different numbers of neutrons
AZX notation where z is the proton number and A is the nucleon number
3.2.1.2 stable and unstable nuclei
the strong nuclear force keeps nuclei stable as it counteracts the electrostatic force of repulsion. it acts in a very short range
unstable nuclei
unstable nuclei are those which have too many protons or neutrons or both
the SNF is not strong enough to keep them stable so the nuclei will decay to become stable
alpha decay
occurs in large nuclei with too many proton and neutrons
the proton number decreases by 2
the nucleon number decreases by 4
beta-minus decay
occurs in large nuclei with too many neutrons
the proton number increases by 1
the nucleon number stays the same
an anti neutrino is also produced to account for energy conservation
3.2.1.3 particles, antiparticles and photons
for every type of particle, there is a corresponding antiparticle
the antiparticles have the same mass and rest energy but opposite charges
antiparticles
electron - positron
proton - antiproton
neutron - antineutron
neutrino - antineutrino
photons
electromagnetic radiation travels in packets called photons, which transfer energy and have no mass
E=hf = hc/l where h is the planck constant
annihilation
where a particle and its corresponding antiparticle collide
the particles masses are converted into energy
the energy is released in the form of 2 photons moving in opposite directions therefore conserving momentum
pair production
when a photon is converted into an equal amount of matter and antimatter
this only occurs when the photon has an energy greater than the total rest energy of both particles
any excess energy is conserved into kinetic energy of the particles
3.2.1.4 Particle interactions
fundamental forces
gravity
acts on particles with mass
infinite range
electromagnetic
virtual photon
acts on all particles with charge
infinite range
weak nuclear
acts on all particles
limited to beta decay, electron capture and electron-proton collisions
strong nuclear
gluon
acts on hadrons
range is 3 fm
exchange particles
these carry energy and momentum between the particles experiencing the force and each fundamental force has its own exchange particle
equations
electron capture: p+e- ----> n + ve Exchange particle: W+ boson
electron-proton collision: p+e- --> n + ve Exchange particle: W- boson
beta-plus decay: p --> n + e+ + ve Exchange particle: W+ boson
beta-minus decay: n --> p + e- + ve- Exchange particle: W- boson
3.2.1.5 Classification of particles
matter and antimatter
hadrons
baryons
mesons
leptons
hadrons
experience strong nuclear force
formed of quarks
baryons
formed of 3 quarks or 3 anti-quarks
the baryon number is always conserves in particle interactions
the proton is the only stable baryon, to which all other baryons decay to
mesons
formed of a quark and an antiquark
leptons
fundamental particles
don't experience the strong nuclear force
lepton number is always conserved in particle interactions
a muon decays to an electron
strange particles
particles produced by the strong nuclear interaction but decay by weak interaction
strangeness is a property of particles which is only conserved in strong interactions
can increase or decrease by 1 in weak interactions
3.2.1.6 Quarks and antiquarks
types of quarks
down
e
strange
charge: -1/3 e
baryon number: + 1/3
strangeness: -1
mesons
3.2.1.7 Application of conservation laws
properties to be conserved
energy and momentum
charge
baryon number
lepton number
strangeness in strong interactions
3.2.2.1 The photoelectric effect
where photoelectrons are emitted from the surface of metal after light above a certain frequency is shone on it. the certain frequency is different for different types of metals known as the threshold frequency
photon model of light
EM waves travel in discrete packets called photons
each electron can absorb a single photon so a photoelectron is only emitted if the frequency is above the threshold frequency
if the intensity of light is increased, is the frequency is above the threshold , more photoelectrons are emitted per second
the work function of a metal is the minimum energy required for electrons to be emitted from the surface of a metal
the stopping potential is the potential difference you would need to apply across the metal to stop the photoelectrons with the maximum kinetic energy. KE max = e x stopping potential
3.C
3.2.2.2 Collisions of electrons with atoms
electrons in atoms can only exist in discrete energy levels
excitation
if an electron becomes excited, it will quickly return to its original energy level, and therefore release the energy it gained in the form of a photon
if electrons gain enough energy from collisions, the can be removed from the atom entirely, known as ionisation
ionisation occurs if the energy of the free electron is greater than the ionisation energy
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