AS - Particles And Radiation Flashcards
Equilibrium point for strong nuclear force
0.5 fm
Maximum attraction for strong nuclear force
2 fm
Nucleus Diameter
3 - 4 fm
Alpha Decay
4 He 2 nucleus
decays to give out mass
short range (5cm in air)
Beta - Decay
0 e -1 fast moving electron
Decays to change n -> p
Releases an antineutrino (takes away energy and momentum)
Beta + Decay
0 e +1 fast moving positron
Decays to change p -> n
Releases a neutrino (takes away energy and momentum)
Gamma Decay
Has no mass or charge (it’s a wave)
Decays to give out energy
Neutrinos
Conserves energy in beta decays
Has no charge and almost no mass
1930 - Wolfgang Pauli found the neutrino
1955 - Neutrino was observed
Atomic Structure
A Na Z
A = p + n (nucleon number)
Z = p = e (proton number)
Isotopes
Same proton number, different nucleon number
Same number of protons, different number of neutrons
Specific Charge
Specific Charge (C/kg) = Charge (C) / Mass (kg)
Proton Charge and Mass
p+
- 6x10-19 C
- 67x10-27 kg
Neutron Charge and Mass
n
0 C
1.67x10-27 kg
Electron Charge and Mass
e-
- 1.6x10-19 C
9. 11x10-31 kg
Photons Equations
EM radiation exists as photons
Energy (J) = Planck’s Constant (Js) x Frequency (Hz)
Energy (J) = Planck’s Constant (Js) x Speed (m/s) / Wavelength (m)
Proton and Antiproton Rest Energy
938MeV
Neutron and Antineutron Rest Energy
939MeV
Electron and Positron Rest Energy
0.511MeV
Neutrino and Antineutrino Rest Energy
0MeV
J to eV and eV to J
J to eV - divide by 1.6x10-19
eV to J - multiply by 1.6x10-19
eV is the work done when an electron moves through a pd of 1V
Pair Production
E min = hf min = 2E
1 photon : 1 particle
Produces particle and antiparticle
Energy (photon) -> mass (e+ and e-)
Annihilation
E min = hf min = E Produces energy (photons) Mass (e+ and e-) -> Energy (2 x photons)
Electron Capture
p+ + e- -> n + Ve
W+ boson
Arrow from proton to electron
Electron - Proton Collisions
e- + p+ -> n + Ve
W- boson
Arrow from electron to proton
Electromagnetic Force
Virtual photon
Affects all charged particles
Infinite range
Weak Nuclear Force
W+ and W- bosons
Affects all particles
Short range
Strong Nuclear Force
Pions
Affects hadrons only
Short range
Gravitational Force
Graviton
Affects anything with mass
Infinite range
Up Quarks
Charge = 2/3
Strangeness = 0
Baryon number = 1/3
Anti Up Quarks
Charge = -2/3
Strangeness = 0
Baryon number = -1/3
Down Quarks
Charge = -1/3
Strangeness = 0
Baryon number = 1/3
Anti Down Quarks
Charge = 1/3
Strangeness = 0
Baryon number = -1/3
Strange Quarks
Charge = -1/3
Strangeness = -1
Baryon number = 1/3
Anti Strange Quarks
Charge = 1/3
Strangeness = 1
Baryon number = -1/3
Lepton Rules
Lepton number must be conserved
e- can only produce Ve
Muon- can only produce Vmuon
Conservation Rules
Energy and charge must be conserved (all reactions)
Lepton numbers must be conserved
Strangeness must be conserved (strong force reactions)
Baryon numbers must be conserved
Hadrons
Strong force
Baryons and mesons
Baryons
QQQ
Proton (uud)
Neutron (udd)
Mesons
Qq
Pion
Kaon
Leptons
Fundamental Weak force Muon Electron Tau Neutrinos
Stopping Potential
Minimum V needed to stop electron emission (Vs)
At Vs, Ek = 0
Ek max = eVs
e = electron charge
Vacuum Photocell
When f > f min in incident light, electrons from cathode are attracted to anode
Ammeter measures photoelectric current
I is proportional to electrons per second
Number of electrons = I / e
Photoelectric Effect In A Photocell
Each photo electron can only absorb one photon
Intensity = number of photons
Ek max = hf - ø
Work Function (ø)
Electrons can leave a metal’s surface if E > ø
f min = ø / h
Excess energy = Ek
Power of a beam P = nhf
Photoelectric Effect Conditions
Incident EM radiation must have f > f min
Frequency depends on metal (f = c / wavelength)
Intensity does not affect electron emission (no delay)
Ionisation
p =/= e
Adding electrons = -
Removing electrons = +
Excitation
Energy is absorbed from colliding electrons without electrons leaving the atom
Energy levels are discrete and only happens at those values
Excitation energy < ionisation energy
Energy Levels
Lowest = ground state Energy = energy level value E of emitted photon = E1 - E2 Uses E from incoming photon Electrons de excite (fall down energy levels) and release a photon
Fluorescent Tubes
Tube contains mercury vapour at low pressure
Power supply => mercury atoms collide and cause ionisation and excitation
Mercury releases UV photons, they’re absorbed by coating and excite
UV de excites to release visible photons
Line Spectra
Every atom has a different composition
Each line of colour corresponds to an energy level
Wave - Particle Duality
Wave - diffraction (spreads out in waves)
Particle - photoelectric effect (1:1 with immediate emission)
De Broglie Wavelength
Wavelength = h / mv
Electron diffraction - electrons are fired through a thin foil slit and spread out producing circles on a screen
pd + = v + = rings - = wavelength - = diffraction -
Electrons diffract by the same amount at the same angle
