Particles and radiation Flashcards
Isotopes
Same proton number but different nucleon number
Atomic structure
Protons and neutrons in nucleus
Electrons in orbit
Charge of Proton
1.6 x 10^-19
Charge of neutron
0
Charge of electron
-1.6 x 10^-19
Mass of proton
1.673 x 10^-27
Mass of neutron
1.675 x 10^-27
Mass of electron
9.11 x 10^-31
Relative charge of Proton, Neutron and Electron
+1 , 0 , -1
Relative mass of Proton, Neutron and Electron
1, 1, 0.0005
Specific charge
Charge/mass = Ckg^-1
Use of strong nuclear force?
Glues the nucleus together
Stronger than electrostatic force (repulsion)
What is alpha decay?
Parent nucleus turns from one nucleus to a daughter nucleus and emits an alpha particle (Helium 4)
Rest energy is conserved
What is beta decay?
A neutron turns into a proton and electron emitted
Releases another nucleus with new atom and higher proton number
Process is meant to conserve energy but beta particles which are emitted have less KE ==> Energy not conserved
Neutrinos is the third particle missing
What are anti-particles?
Every particle has a corresponding antiparticle with the same mass but opposite charge
Anti particle of an electron?
Positron
Antiparticle of a proton?
Antiproton
Antiparticle of a neutron and neutrino
Antineutron and antineutrino
What is rest energy?
The energy a particle with any amount of mass has even while stationary
Measured in MeV
Antiparticle has the same rest energy as their corresponding particle
What is a photon?
A quantum of EM radiation
Quanta (discrete packets of energy)
No mass
How to calculate energy of a photon?
E = hf
E = energy carried (Joules)
h = Planck’s constant
f = frequency
What is Planck’s constant?
6.63 x 10^-34
Wave speed in this case?
C = f x wavelength
f = c/wavelength
E=hf or
E=h c/wavlength
Annihilation
Conversion of a particle and antiparticle into a pair of gamma ray photons where the rest energy of the particle and antiparticle is converted into the energy of the photons
Photons travel in opposite directions
Total energy when annihilation occurs at rest?
2 x rest energy of particle
Total energy when annihilation occurs when moving
(rest energy of particle + KE of particle) + (rest energy of antiparticle + KE of antiparticle)
What is pair production?
Defined as the process in which a photon is converted into a particle and its own particle in the presence of matter where the energy of the photon is converted to rest energy of particle and anti particle
What is the path in pair production
Curved away from each other as in the presence of a magnetic field they have opposite charge
Energy in pair production
Energy of photon is converted to rest energy of particle and antiparticle
Excess energy goes to KE
Min energy required for pair production = 2 x rest energy of electron
Four fundamental forces
Electromagnetic
Weak nuclear (Nuclear decay)
Strong nuclear (holds the nucleus)
Gravity (ignored in PP)
Gravity
Infinite range
Acts on anything with mass
So weak it can be ignored in PP
Electromagnetic
Force between all charged particle
Infinite range
Examples -> Annihilation and repulsion of 2 electrons
Strong nuclear force
Only acts between hadrons and not leptons
Strongly attractive between 0.5fm and 3fm
Repulsive at less than 0.5 fm
Non existent at great than 3fm
How much is one fm?
1 x 10^-15
Weak nuclear force
Responsible for beta decay and decay of muons and strange hadrons
Acts on all hadrons and leptons
Conserves charge, baryon and lepton numbers
Charge including neutrino must be weak
Exchange particles
Also known as gauge bosons
Known as virtual particles as they are short lived and cant be caught
Definition of exchange particles?
Virtual particles which may exist for only a short amount of time and are the mediators of a force by transferring energy and momentum between particles
Exchange particle for electromagnetism?
Virtual photon
Electron orbits a proton and exchange virtual photons
Photons have no mass and no charge
Exchange particle for weak nuclear force?
Weak boson
Two types (W+ and W-)
Have the same mass and a relative charge of +1 and -1
Acts on all particles
Exchange particle for strong nuclear force
Pions
pi +, pi - and pi 0
Exchange particle for gravity
Only hypothetical gravitons
Never been indirectly or directly observed
Use of Feynman diagram
Way to visualise how these particle interact
How Feynman diagram works
Lines at the bottom represent the starting
Those at the end represent the ending particles
Squiggly line drawn crossing is the exchange particle
Angle and direction don’t mean anything
Time flows from bottom to top
Electromagnetic interactions
No change in particles
Normally between proton and electron
e- + p –> e- + p
Virtual photon emitted by both particle and exchanged
Strong nuclear interactions
Between a proton and a neutron
p + n –> p + n
Emit and exchange virtual pions
Nuclear minus beta decay
Neutron turns into a proton
n –> p +e- + antineutrino
W- boson is emitted turning into an electron and anti neutrino
Nuclear plus beta decay
Proton into a neutron, positron and neutrino
p –> n + e+ + neutrino
W + boson emitted
Electric charge conserved
Hadrons
Particles that experience the strong nuclear force
What are the two classifications of hadrons?
Baryons and Mesons
What are baryons
Heavier hadrons like protons and neutrons
Proton is he only stable baryone
Have a baryon number of +1 (anti have -1)
Contains 3 quarks
What are mesons
Lighter hadrons like pions and kaons
Comprise of a quark and anti-quark
Lightest hadron and mesons are the pions
pi + and pi - are particle and antiparticle duo
Kaons decay into pions
What are leptons?
Particles which don’t interact with strong nuclear force
Electrons, muons, electron nuetrino and muon neutrino
Lepton number of +1 and -1
Muons decay into electron and both neutrinos –> same charge as electron
What are strange hadrons?
Hadrons heavier than the pions - produced by strong nuclear force
K+, K-, K0
Strangeness can be from -3, to +3
K+ has +1 strangeness and K- has -1 strangness
Strangness is conserved in electromagnetic and strong interactions
Not conserved when they decay by weak nuclear
What are quarks?
Fundamental particles which make up the old fundamental particles
Have charges of + or - 2/3 and + or - 1/3
What are the three types of quarks and their relative charge?
Up +2/3
Down -1/3
Strange -1/3
What is the strangeness of all 3 quarks?
Up - 0
Down - 0
Strange - -1
What is heavier, strange quarks or up and down quarks?
Strange quarks
Explains the difference in mass of strange and normal hadrons
Baryon number of quarks and anti-quarks
+1/3
-1/3
Quark composition of proton and neutron
Proton - uud
Neutron - udd
Quark composition of antiproton and antineutron
Anti-p = anti uu and anti d
Anti-n = anti u and anti dd
Quark composition of mesons (Pion and kaon)
Pion - u and anti d
Kaon - u and anti s
All interactions obey the conservation of?
Energy and momentum
Interactions by one of the four fundamental forces conserve?
Charge
Baryon number
Lepton number
Electromagnetic and strong nuclear force always conserve?
Strangeness
However, strangeness can decay during interactions mediated by the weak nuclear force
What happens to the quarks during beta minus decay
Neutron turns into a proton
Down quark changes to an up quark
What happens to quarks during beta plus decay?
Proton turns into a neutron
Up quark changes to a down quark
Photoelectric effect
When a metal surface is illuminated by electromagnetic radiation above a certain frequency, the delocalised electrons are liberated from the metal
Electrons are known as photo electrons
What is the kinetic energy of these photoelectrons?
Can vary from 0 to a maximum
What is the threshold frequency of a metal
The minimum frequency required of EM radiation for photoelectrons to be emitted from the metal
Energy is needed to overcome electrostatic forces of attraction of ions
What is the work function?
The minimum energy needed for electrons to escape the metal
What happens when EM radiation is below the threshold frequency?
No photoelectrons are emitted
Increased intensity does not lead to the emission of photoelectrons
What happens to EM radiation above the threshold frequency?
Some photoelectrons emitted instantaneously
The intensity has no effect on the kinetic energy
Increasing frequency increases the number of photoelectrons emitted
Why is there a threshold frequency?
It is a one to one effect where a single electron absorbs a single photon
Equation in photoelectric effect?
hf = ϕ + Ek(max)
h = Planck’s Constant
f = frequency (Hz)
hf = energy of a photon (J)
ϕ = Work function (J)
E = Maximum kinetic energy of the emitted photoelectrons
When the energy of the photon is equal to the work function …
The kinetic energy of the emitted photoelectron will be 0
Work function is then h x f
Where f is the threshold frequency
Graph of Maximum KE against frequency
Ek Max = hf - work function
y = mx + c
Planck’s constant is the gradient
Negative of the work function is the y intercept
Threshold frequency is the x-intercept
Excitation
The process of an atomic electron absorbing a discrete amount of energy and moving from a lower energy level to a higher energy level
The energy absorbed must be equal to the difference in energy between energy levels
When does excitation occur?
When a single electron absorbs a single photon or kinetic energy during a collision with a charged particle
De-excitation
When atomic electron moves from higher energy level to lower energy level, emitting a photon of EM radiation
Excited state is unstable and so de-excitation occurs
Ionisation
When an electron absorbs sufficient energy to be removed from an atom, creating a positive ion and a free electron
Ionisation energy
Minimum energy required to remove an electron from its ground state in an atom
= to magnitude of the ground state energy of electron
Electron Volt
eV = 1.6 x 10^-19 J
MeV = 10^6 x 1.6 x 10^-19J
De Broglie’s Hypothesis
Light behaved as both a particle and a wave
So any particle can exhibit wave-like properties and behaviour
De Broglie’s wavelength
wavelength = h/mv
Wavelength is inversely proportion to momentum of the particle
Electron diffraction
Electrons pass through tin foil and diffract
Produce regions of constructive and destructive interference
Pattern of rings with different intensities
Individual particles still detected
Emission line spectra
A series of discrete wavelengths of light
Each element has its own distinct spectrum
How to figure out frequency of light during de-excitation?
Difference in energy between the levels
hf = E2-E1
What happens in fluorescent tubes?
Electric current flows through - freely moving electrons with KE
Collide with electrons in the atoms of the low pressure gas
Collide and KE is transferred so atomic electrons excite and deexcite and emit photons of UV light
UV photons absorbed by the electrons in the coating o the tube causing them to be excited
Atomic electrons de-excite ad emit photons of visible light
How can electrons de-excite?
Can de-excite in various waves causing a line spectrum
Can jump energy levels or go one by one
Energy of the photons emitted are ..?
Low than those o the UV photons absorbed so the frequency are lower and thus similar to visible light
