Particles and Radiation Flashcards
What is a nucleon?
A particle in the nucleus (protons and neutrons)
What is the relative mass of an electron?
1/1840
What is the proton number?
Number of protons in the nucleus
What defines what an element is?
The number of protons
What do an element’s reactions and chemical behaviour depend on?
Number and arrangement of electrons
What is the mass number?
Number of protons and neutrons in the nucleus
In physics, what does ‘specific’ mean?
Per unit mass
What is the specific charge of a particle?
The ratio of its charge to its mass
What is the SI units of specific charge?
C kg^-1
What is the equation for specific charge?
Specific charge = Charge / Mass
What is a fundamental particle?
A particle that cannot be split up into anything smaller, such an electron
What is an isotope?
An atom of an element with the same number of protons, but a different number of neutrons
What does changing the number of neutrons of an atom affect?
The stability of the nucleus
In general, the greater the number of neutrons compared with the number of protons…?
The more unstable the nucleus is
What do unstable nuclei do?
Decay to make themselves more stable
What isotopic data?
The relative amounts of isotopes in a substance
What is the electromagnetic force?
A fundamental force that causes interactions between charged particles
What does the electromagnetic force cause in the nucleus?
The positively charged protons to repel each other
What does the gravitational force in the nucleus cause?
All the nucleons in the nucleus to attract each other due to their mass
Which is a bigger force in the nucleus, the repulsion from the electromagnetic force or attraction from the gravitational force?
The repulsion from the electromagnetic force
What is the strong nuclear force?
A fundamental force with a short range which is attractive at short separations, but repulsive at very small separations
What is the strong nuclear force responsible for?
The stability of the atom
What are interactions that use the strong nuclear force called?
Strong interactions
What separation of nucleons is the strong nuclear force repulsive for?
Less than 0.5 fm (5x10^-16 m)
Describe the strong nuclear force once the nucleon separation has increased past 0.5 fm?
The strong nuclear force becomes attractive, reaching a maximum attractive value, the falling rapidly to zero after about 3 fm (3x10^-15)
What is nuclear decay?
When unstable nuclei will emit particles to become more stable
What is an alpha particle?
The nucleus of a helium atom
Alpha decay can only happen in…?
Very large atoms with more than 82 protons
Why are very large atoms, such as uranium, very unstable?
Because they’re so big that the strong nuclear charge can’t keep them stable
How do very large atoms become more stable?
They release an alpha particle from their nucleus
What happens to the proton number when an alpha particle is released from the nucleus?
The proton number decreases by 2
What happens to the mass number when an alpha particle is released from the nucleus?
The mass number decreases by 4
Describe the range of an alpha particle in air
Only a few cm
What does a Geiger Counter do?
Measure the amount of ionising radiation
How does a Geiger counter work?
The counter consists of a tube filled with an inert gas that becomes conductive of electricity when it is impacted by a high-energy particle. When a Geiger counter is exposed to ionizing radiation, the particles penetrate the tube and collide with the gas, releasing more electrons
What is beta-minus decay?
The emission of an electron from the nucleus along with an antineutrino particle
What does beta decay normally occur with?
Isotopes that are ‘neutron rich’ (have to many neutrons compared to protons)
What happens when the nucleus ejects a beta particle?
One of the neutrons in the nucleus turns into a proton
Which has a greater range, alpha or beta particles?
Beta particles can travel a few metres in air
What is the evidence that the electron wasn’t the only particle to be emitted in beta-minus decay?
The energy of the particles before the beta decay was less than the energy before, which goes against the principle of the conservation of energy
What did Wolfgang Pauli suggest about beta decay in 1930?
That another particle was being emitted that carried away the missing energy
What would have to be 2 characteristics of the other particle that Pauli suggested was emitted in beta decay?
Neutral (or charge won’t be conserved)
Almost zero mass (as it had never been detected)
What is the other particle that is emitted in beta decay called?
Electron Antineutrino ( ̅νe)
What is the electromagnetic (EM) spectrum?
A continuous spectrum of all the possible frequencies of EM radiation
What are the 7 different types of EM radiation (in order of increasing wavelength)
Gamma X-Ray UV Visible Light Infrared Microwave Radio
Which has a bigger wavelength, gamma rays or radio waves?
Radio waves
Which has a bigger frequency, UV or visible light?
UV
Which has a bigger frequency, gamma rays or radio waves?
Gamma rays
The higher the frequency of the EM radiation, the…?
Greater its energy
What are photons?
Packets of EM radiation
How suggested that EM waves only existed in discrete packets called photons?
Einstein
What is the equation for the energy of a photon (in J)?
E = hf
In the equation for the energy of a photo, what does the h mean?
Planck’s constant (6.63x10^-34 Js)
In the equation for the energy of a photo, what does the f mean?
Frequency of light, Hz
What equation links the energy of a photon, Planck’s constant, wavelength and speed of light in a vacuum?
E = (hc) / λ
What is an antiparticle?
A particle with the same rest mass and energy as its corresponding particle, but an equal and opposite charge
What is an antiproton?
A negatively charged particle with the same mass as a proton
What is matter?
Name given to all particles
What is antimatter?
Name given to all antiparticles
What is pair production?
A process of converting energy to mass in which a gamma ray photon has enough energy to produce a particle-antiparticle pair
What do you get when energy is converted into mass?
Equal amounts of matter and antimatter
Pair production can only happen if there is enough of what?
If there is enough energy to produce the masses of the particles
Why do you need a large amount of energy to fire 2 protons at each other to make them collide?
Because they’re both positively charged, so they repel each other
If a photon has enough energy, what can be produced from 2 photons being fired into each other?
An electron-positron pair
When does an electron-positron pair most commonly get produced?
When a photon passes near a nucleus
What is the minimum amount of energy needed for pair production?
The total of the rest energy of the particles that are produced
What is rest energy?
The amount of energy that would be produced if all the particle’s mass was converted to energy
What is the minimum amount of energy need for pair production equal to?
2 x rest energy of particle (Emin = 2Eo)
How do you convert MeV to J?
Multiply by 1.60 x10^-13
Why do you normally get electron-positron pairs produced, rather than any other pair?
Because they have a relatively low mass, so less energy is need for pair production to happen
What is it called when a particle meets its antiparticle?
Annihilation
What is annihilation?
The process when a particle and antiparticle meet and their mass gets converted to energy in the form of a pair of gamma ray photons
What happens in annihilation to conserve momentum?
The 2 gamma ray photons travel in opposite directions
What is the equation for the minimum energy of photon produced during annihilation?
Emin = Rest energy of particle produced
What does PET scanner stand for?
Positron Emission Tomography scanner
How does a PET scanner work?
In hospitals they’ll put a positron-emitting isotope into the bloodstream, then detect the gamma rays that are produced by the annihilation that occurs
In a PET scanner, what detects the radiation?
A scintillator
How does a scintillator work?
Contains scintillation crystals which produce a flash of light when a gamma ray hits them. These flashes of light can be detected and used to form an image
What are hadrons?
Particle made up of quarks that is affected by the strong nuclear force
Are hadrons fundamental particles or not?
They’re not fundamental, because they’re made up of smaller particles called quarks
What are the 2 types of hadron?
Baryons
Mesons
Give 2 examples of a baryon
Proton
Neutron
What can be said about the stability of baryons?
All baryons except a free proton, can be unstable meaning they decay to become other particles
What baryon doesn’t decay, and therefore is stable?
Proton (and anti-proton)
What do all baryons, except a proton, decay into?
A proton
Give 2 examples of anti-baryons
Anti-proton
Anti-neutron
Why don’t you find anti-baryons in normal matter?
Because they’re annihilated by their corresponding particle
What is the baryon number?
The number of baryons
What can be said about the baryon number?
It is a quantum number that is conserved
What is a quantum number?
A number that represents a property of a particle that must be conserved in all interactions
What is the baryon number of protons and neutrons?
+1 (because they’re both baryons)
What is the baryon number of anti-baryons?
-1
What baryon number is given to particles that aren’t baryons?
0
The total baryon number in any particle interaction…?
Never changes
What is formed when a neutron decays?
Proton + electron + antineutrino
How do mesons interact with the baryons?
Via the strong force
What can be said about the stability of mesons?
All of them are unstable
What is the baryon number of all mesons?
0 (because they’re not baryons)
Which is the lightest type of meson?
Pion (π+, π0, π-)
What is the antiparticle of π+?
π-
What is the antiparticle of π0?
Itself
Which force are pions the exchange particle for?
Strong nuclear force
Compare Kaons (K+, K0, K-) with the pions?
Kaons are heavier and more unstable
What do kaons decay into?
Pions
What are cosmic rays?
Radiation in the form of charged particles that come from Space and hit Earth
What are cosmic ray showers?
Lots of high-energy particles that are produced from cosmic rays interacting with molecules in the atmosphere
What are leptons?
Fundamental particles that don’t feel a strong nuclear force
Name a stable lepton
The electron
Give 2 examples of leptons
Electrons
Muons
How do leptons interact with other particles?
Via the weak interaction (as well as gravitational potential and electromagnetic if they’re charged)
What is a muon?
A heavier electron that is very unstable
What do muons decay into?
Electrons
What is the neutrino of the electron?
Electron neutrino (ν e)
What is the neutrino of the muon?
Muon neutrino (ν μ)
What is the mass and charge of neutrinos?
Almost zero mass and zero charge
What is the antiparticle of the electron?
Positron
What is the antiparticle of the muon?
Antimuon
What is the lepton number?
A quantum number that is the number of leptons
What is the lepton number of the leptons?
+1
What is different about the lepton number of the electron compared to the muon?
They have to be counted separately as L e for electron lepton number and L μ for muon lepton number
What is the lepton number of the corresponding anti-particles of the leptons?
-1
In all particle interactions, what must be conserved?
Lepton number and Baryon number
How do you check to see if a particle interaction can occur?
See if baryon number and lepton number are conserved
How are strange particles created?
Via the strong interaction, in which strangeness is conserved
What is strangeness?
A property which particles that contain strange quarks have. Strange particles are always produced in pairs
Why are strange particles always produced in pairs?
Because of the conservation of strangeness
Describe the stability of the strange quark (and antiquark)
Very unstable
What do strange quarks decay into?
An up quark, electron and an electron antineutrino
What is the strangeness value of leptons?
0
In a strong interaction, what 4 things are conserved?
Baryon number
Strangeness
Total number of quarks
Type of quark
In a weak interaction, what 2 things are conserved?
Total number of quarks
Baryon number
In a weak interaction, what 2 things are not conserved?
Strangeness
Type of quark
If strangeness is conserved, which type of interaction will it always be?
Strong interaction
In any particle interaction, the total charge after the interaction must equal what?
The total charge before the interaction
How is the conservation of charge shown in the pair production of a photon?
A photon with enough energy will produce an electron-positron pair. It couldn’t produce just one of them, because the charge before the interaction is 0, so the charges need to cancel out (+1 -1)
In any particle interaction, the baryon number after the interaction must equal what?
The baryon number before the interaction
When a proton is produced in pair production, how is the conservation of baryon number shown?
Proton has a baryon number of +1, so an anti-proton is produced as well, with a baryon number of -1
What are baryons made of?
3 quarks
What are mesons made of?
1 quark and 1 anti-quark
What is the symbol equation for proton-antiproton pair production?
p + p —> p + p + p̄ + p
Are the electron and muon lepton numbers conserved?
Yes
What type of interaction is the only interaction where strangeness is conserved?
Strong interaction
What is the only way to change the type of quark?
Via a weak interaction
What are the 3 types of quark?
Up quark (u) Down quark (d) Strange quark (s)
What are the 2 types of quark you need to make a nucleon?
Up and down quark
What is the quark composition of a proton?
duu
What is the quark composition of a neutron?
ddu
What do the properties of a particle depend on?
Properties of the quark that make it up
What are the 3 types of anti-quark?
anti-proton
anti-neutron
anti-strange
What are the properties of anti-quarks compared to quarks?
Opposite
What are anti-baryons made of?
3 anti-quarks
What is the quark composition of leptons?
Leptons aren’t made of quarks as they’re fundamental particles
What is the quark composition of π 0?
ŪU, d̅ d or SŠ (all 1 quark and 1 anti-quark)
What is quark confinement?
The idea that quarks can’t be isolated
What is the equation for beta-plus decay?
p —> n + e+ + Ve
What type of interaction is beta-minus decay?
Weak interaction
How do we know that beta-minus decay is a weak interaction?
Because of the quark composition
n —> p
u —> u
d —> u type of quark is not conserved so weak
d —> d
What is a quark changing into another quark known as?
Changing the quark’s character
What are all forces caused by?
Particle exchange
What are gauge bosons?
A virtual particle which allows forces to act in a particle interaction. They’re known as exchange particles
What is an exchange particle?
A virtual particle which allows forces to act in a particle interaction. They’re also known as gauge bosons
What is a virtual particle?
A particle that only exists for a small amount of time
What is the electrostatic force of repulsion between 2 protons caused by?
By the exchange of virtual photons (the exchange particles of the electromagnetic force)
What is the gauge boson of the strong nuclear interaction?
Pions
What particles are affected by the strong nuclear interaction?
Hadrons only
What is the gauge boson of the electromagnetic force?
Virtual photon
What particles are affected by the electromagnetic force?
Charged particles only
What is the gauge boson of the weak nuclear interaction?
W+, W- bosons
What particles are affected by the weak nuclear force?
All types of particle
What are the 4 fundamental types of interaction?
Strong
Weak
Electromagnetic
Gravity
What determines the range of a force?
The size of the exchange particle
Describe the range, and therefore the range of the force, of a heavier exchange particle
Heavier exchange particles have a shorter range, so the force has a shorter range
Why does the weak interaction have a very short range?
Because W bosons are around 100 times as heavy as a virtual photon, and they use so much energy they can’t exist for very short time and can’t travel far. All this means that the weak interaction has a short range
Why does the electromagnetic force have an infinite range?
Because virtual photons have almost zero mass, so it doesn’t use much energy and can travel further
In Feynman Diagrams, what do squiggly lines represent?
Exchange particles
In Feynman Diagrams, what do straight lines represent?
Particles (not exchange particles)
What are the 4 rules for drawing Feynman diagrams?
- Time starts at the bottom and works up (so incoming particles start at bottom)
- Baryons stay on one side of diagram and leptons stay on other side
- The W bosons carry charge from one side of diagram to the other
- A W- particle travelling left is the same as a W+ particle travelling right
What is beta-minus decay?
When a neutron decays into a proton, electron and antineutrino
What is electron capture?
The process of a proton-rich nucleus capturing an electron to turn a proton into a neutron, emitting a neutrino
What is the formula for electron capture?
p + e- —> n + Ve
How is an electron-proton collision Feynman diagram different to that of electron capture?
Has a W- boson coming from the electron, because the electron is acting on the proton, whereas in electron capture it’s a W+ boson from the proton because the proton is acting on the electron
