Particles and Radiation Flashcards
Imported 07/03
Charge of a proton/electron
1.6x10^-19
Mass of proton/neutron
1.67x10^-27
Mass of electron
9.11x10^-31
Specific charge formula
Charge/mass
What are isotopes
Atoms with the same number of protons but diff number of neutrons
What is carbon dating
Calculating percentage of carbon-14 remaining in object, using known starting value (same for all living things) and half life to calculate approximate age
What is the strong nuclear force
Keeps nuclei stable, counteracts electrostatic force, only acts on nucleons, very short range, attractive up to 3fm, repulsive below 0.5fm
What is an unstable nuclei
Has too many protons, neutrons or both, strong nuclear force not enough to keep them stable, nueclei will decay to become stable
Where and how does alpha decay occur
Large nuclei, too many protons AND neutrons, 2 protons, 2 neutrons
Where and how does beta minus decay occur
When too many neutrons, proton number increases by 1, lose 1 electron
What did observation of energy levels in beta decay lead to
The discovery of the neutrino
Particles and antiparticles common properties
Rest energy and mass
How does electromagnetic radiation travel
In photons
What is the energy of photons directly proportional to
Frequency
Energy and planck constant formulas
E = hf = hc/?
What is annihilation
Particle and corresponding antiparticle collide, masses converted to energy, 2 photons moving in opposite directions are released to conserve momentum
Application of annihilation
PET scanner - 3D images of inside body taken, introducing positron emitting radioisotope into patient, positrons annihilate, releases gamma photons which can be easily detected
What is pair production
Photon collides with matter (to conserve momentum) and is converted into equal amount of matter and antimatter, only occurs when photon has energy > total rest energy of both particles, any excess energy is converted to kinetic
What are the 4 fundamental forces
Gravity, electromagnetic, weak nuclear force, strong nuclear force
What are forces between particles caused by
Exchange particles
What are exchange particles
Carry energy and momentum between particles - ball vs boomerang analogy
Exhange particle for strong force
Gluon
Range of strong force
3fm
What does strong force act on
Hadrons
Exhange particle for weak force
W boson (+ or -)
Range of weak force
10^-18
What does weak force act on
All particles
Exhange particle for electromagnetic force
Virtual photon (?)
Range of electromagnetic force
Infinite
What does electromagnetic force act on
Charged particles
Exhange particle for gravity
Graviton (theoretical)
Range of gravity
Infinite
What does gravity act on
Particles with mass
Examples of what the weak force is
responsible for
Beta decay, electron capture, electron-proton collisions
What causes beta decay, electron capture and electron-proton collisions
Weak force
Electron capture formula
p+e=n+Ve
Electron-proton collision formula
p+e=n+Ve
Exchange particle in electron capture
W+
Exchange particle in electron-proton collision
W-
Direction of arrow in electron capture
p to e (left to right)
Direction of arrow in electron-proton collision
e to p (right to left)
Beta plus decay formula
p = n + e^+ +Ve
Beta minus decay formula
n = p + e + Ve(anti)
Exchange particle in beta plus decay
W+
Exchange particle in beta minus decay
W-
Direction of arrow in beta plus decay
p to Ve (left to right)
Direction of arrow in beta minus decay
n to Ve (left to right)
What are leptons
Fundamental particles - do not experience strong nuclear force
What are hadrons
Formed of quarks, experience strong nuclear force
What are the classifications for fundamental or non-fundamental particles
Hadrons and leptons
Subcategories for hadrons
Baryons, antibaryons and mesons
What are baryons
Type of hadron, formed from 3 quarks
What are antibaryons
Type of hadron, formed from 3 antiquarks
What are mesons
Type of hadron, formed from a quark and an antiquark
Examples of leptons
Electron, muon, electron neutrino, muon neutrino, (and their antiparticles)
Examples of baryons
Proton or neutron
Examples of mesons
Pion, kaon
Baryon number
1 if baryon, -1 if antibaryon, 0 if not a baryon, conserved in particle interactions
What is the only stable baryon
Proton
What are special about protons as baryons
Only stable one
Why is it important that protons are the only stable baryon
All baryons eventually decay into protons
Lepton number
1 if lepton, -1 if antilepton, 0 if not a lepton, 2 types, electron lepton and muon lepton, lepton number always conserved in particle interactions
What are muons
Known as heavy electrons, decay into electrons
Production and decay of strange particles
Produced by strong nuclear interaction, decay by weak interaction
Strange particles example and decay
Kaons decay into pions via the weak interaction
Conservation of strangeness
Strange particles must be created in pairs as strangeness must be conserved in strong interactions, in weak interactions, strangeness can change by -1, 0 or 1
Investigation of particle physics
Particle accelarators can be used, expensive to build and run, produce huge amounts of data, scientific investigations rely on collaboration of scientists internationally
Properties of quarks
Charge, baryon number, strangeness
3 types of quarks
Up, down, strange
Charge of up
+2/3 e
Baryon number of up
+1/3
Strangeness of up
0
Charge of down
-1/3 e
Baryon number of down
1/3
Strangeness of down
0
Charge of strange
-1/3 e
Baryon number of strange
+1/3
Strangeness of strange quark
-1
How do the charge, baryon number and strangeness of a quark change for antiquarks
Opposite sign
Quark combination for ?0
u(anti)u or d(anti)d
Quark combination for ?+
u(anti)d
Quark combination for ?-
(anti)ud
Quark combination for k0
d(anti)s or (anti)ds
Quark combination for k+
u(anti)s
Quark combination for k-
(anti)us
Charge for ?0
0
Charge for ?+
1
Charge for ?-
-1
Charge for k0
0
Charge for k+
1
Charge for k-
-1
Strangeness for ?0
0
Strangeness for ?+
0
Strangeness for ?-
0
Strangeness for k0
+/- 1
Strangeness for k+
1
Strangeness for k-
-1
Equation for neutron decaying into proton
n = p + e + Ve(anti)
What properties must always be conserved in particle interaction
Energy and momentum, charge, baryon number, electron lepton number, muon lepton number
When is strangeness conserved
During strong interactions
What doesn’t have to be conserved during decay
Strangeness
Why are beta minus and plus decay caused by weak interaction
Because there is a change of quark type
Change of quark in beta minus decay
D into U
Change of quark in beta plus decay
U into D
What is the threshold frequency
Minimum frequency that needs to be shone on a metal for photoelectrons to be emitted from the surface
How does the photoelectric effect contradict the wave theory
Wave theory says that any frequency of light should cause photoelectric emission as energy absorbed would gradually increase with each wave
How does the photon model of light explain the photoelectric effect
Each electron can absorb a single photon, so photoelectron only emitted if frequency is above the threshold frequency (E=kf), as intensity increases, more photoelectrons are emitted per second
What is the work function of a metal
Minimum energy required for electrons to be emitted from the surface of a metal, ?
What is the stopping potential
Potential difference that would need to be applied across the metal to stop the photoelectrons with the max kinetic energy
What can finding the stopping potential do
Allows you to find the max kinetic energy of the released photoelectrons, E(max kinetic) = eVs - e = charge of electron and Vs = stopping potential
Photoelectron equation
E = hf = ? + E(max kinetic)
How does the energy of electrons in atoms work
Discrete energy levels
What is it called when an electron moves up an energy level
Excitation
How can electrons gain the energy to move up an energy level
Via collisions with free electrons
What happens when an electron in an atom gain energy
Excitation or being removed from the atom entirely
What is it called when an electron is removed from the atom
Ionisation
What condition has to be met for ionisation to occur
Energy of free electron > ionisation energy
What happens after an electron gets excited and moves up a level
Quickly returns to original energy level (ground state), so releases energy it gained in the form of a photon
Example of a practical use of excitation
In a fluorescent tube to produce light, tube filled with mercury vapour, high voltage applied across it, voltage accelerates free electrons through tube, collide with mercury atoms which become ionised, releasing more free electrons, cause mercury atoms to become excited, when they de-excite they release photons, mostly within UV range, fluorescent coating on inside of tube absorbs the photons and so electrons in atoms of coating become excited and de-excite releasing photons of visible light
Units for small values of energy
Electron volt
What is an electron volt
Energy gained by one electron when passing through a potential difference of 1 volt
How many joules are in an electron volt
1.6 x 10^-19
What is bigger, electron volt or joule
Joule
How to convert from electron volt to joule
x by 1.6x10^-19
How to convert from joule to electron volt
Divide by 1.6x10^-19
What happens when pass a light from fluorescent tube through diffraction grating or prism
Get a line sprectrum
What does each line in a line sprectrum represent
A diff wavelength
Is the line spectrum for a fluorescent tube continuous or discrete
Discrete
How is a discrete line spectrum evidence for discrete energy levels
The photon energies emitted will correspond to the wavelengths, so evidence that atoms can only transition between discrete energy levels
What happens when you pass white light through a cooled gas
Line absorption spectrum
How to get a line absorption spectrum
Pass white light through a cooled gas
What does a line absorption spectrum look like
Continuous spectrum of all possible wavelengths with black lines at certain wavelengths
What do the black lines on a line absorption spectrum represent
Possible differences in energy levels - atoms can only absorb photons of an energy equal to exact difference between two energy levels
Change in energy formula using discrete energy lines
?E = E1 - E2 where E1 and E2 are energy levels so hf = E1 - E2
What 2 properties can light be shown as having
Wave and particles
Examples of light acting as a wave
Diffraction, interference
Example of light acting as a particle
Photoelectric effect
De Broglie’s equation linking momentum and wavelength
wavelength = h/mv
What happens to the wavelength and diffraction when the momentum is increased
Both decrease
What happens to the wavelength and diffraction when the momentum is decreased
Both increase
How does knowledge and understanding of any scientific concept change over time
In accordance to the experimental evidence gathered by scientific community
Does knowledge and understanding of scientific concepts change over time
YES
What must happen to experimental evidence before it is accepted
Be published to allow for peer-review by scientific community to become validated
Why is the weak force responsible for decay
Change of quark
