Particles Flashcards
What is the nucleon number
Number of protons and neutrons and tell you atoms mass (mass number)
What is the equation for specific charge
SC = charge/mass
What is specific charge and what is it measured in?
This is the ratio of the charge of a particle to it mass and its measured in Ckg-1
What is an isotope?
Atoms with the same number of protons but different number of neutrons
What does changing number neutrons effect and doesn’t effect?
- doesn’t effect chemical properties
- effects nucleus’ stability ( more neutrons compared to protons = more unstable)
- may be radioactive and decay to become more stable
What is isotopic data?
This is the relative amounts of different isotopes of an elements in a substance
why is most of the atom empty space?
Electrons orbit at large distances
What is mass and charge of particles measured in?
Charge = coulombs Mass = kilograms
What does chemical behaviour and element reactions depend on?
Number of electrons in the atom
- Describe alpha decay
- describe alpha particle and what to use to measure the,
- happens in big atoms ( more than 82 protons) - nucleus’ are too big for the strong force
- to make themselves stable they emit an Alpha particle from the nucleus
- LEARN THE EQUATION
- alpha particles have a short range (few cm in air)
- observed using cloud chamber/ Geiger or spark counter
- spark measures ionisation amounts
- describe beta decay
- describe beta particle
- it’s the emission of an electron from the nucleus along with an antineutrino
- when nucleus ejects beta particle, a neutron from nucleus is changed to a proton
- LEARN THE EQUATION
- happens in neutron rich isotopes
- antineutrino carries away some energy and momentum
- range is several metres in air
Describe the hypothesis of neutrinos
- 1930, Wolfgang Pauli said that another particle was emitted and carried the missing energy ( had to be neutral so charge was conserved and had to have zero or almost no mass as it would be hard to detect)
- other discoveries led to the neutrino being accepted and detected 25 years later
Describe why Wolfgang Pauli thought there was another particle emitted in beta decay
- originally it was thought that the only particle emitted in beta was an electron
- observations showed energy was lost which didn’t fit conservation of energy
What is the electromagnetic force?
Causes positive protons to repel each other
What is the gravitational force?
Causes all nucleons in nucleus to attract each other due to their mass
What is the strong force and its range?
- Works equally between all nucleons
- at very small separations it’s repulsive (stops it crushing the nucleus)
- to hold nucleus together must be attractive force stronger than electromagnetic
- has very short range, only holds nucleons when separated by a few femtometers (strength falls after this)
Learn the diagram that shows how the strong force and electromagnetic force interact
Please do it
What is a femtometer?
1 fm = 1x10^-15 (size of nucleus)
What is annihilation?
This is when a particle meets its antiparticles, all mass is converted to energy, in the form of 2 gamma ray photons
How do you calculate minimum energy of the photon in annihilation?
- Min energy of photon = rest energy of particle annihilated in MeV (Emin=Eo)
- between particle-antiparticle which have rest energy Eo. The 2 photons have total energy of 2Eo for energy to be conserved,
- 2Emin = 2Eo
What does a PET scanner do? And how do they work?
- work by putting a positron emitting isotope into a bloodstream and detecting the gamma rays produced by electron-positron annihilation
- gamma rays produced in pairs moving in opposite directions, so easy to distinguish from other gamma rays
- radiation is detected by a scintillator
How did Planck and Einstein come up with photons?
- Planck suggested EM waves can only be released in discrete packets or quanta
- Einstein suggested that EM waves and their energy only exist in discrete packets (photons)
What is the equation for energy?
E = hf h = Planck's constant (6.63x10^-34 Js) f = frequency is Hz
How are frequency, wavelength and SOL related?
E = hf
f = c/wavelength
So E = hc/wavelength
What is frequency and what does it mean about energy?
Frequency is the number of complete waves passing a point per second, higher frequency means greater energy
What is the electromagnetic spectrum and what is it split into?
- It’s a continuous spectrum of all possible frequencies of EM radiation
- split into 7 types based on frequency and properties
What is wavelength?
The distance between two adjacent crests of a wave
What is an antiparticle?
- A particle made of antimatter
- Each particle has one
- they have the same mass and rest energy but different charge
What happens when energy is converted to mass?
You get equal amounts of matter and antimatter
When does pair production happen?
- When there is enough energy to produce masses of the particles
- must produce a particle and its antiparticle because quantities must be conserved
What does the particle-antiparticle pair both have? And what does this mean?
- Rest energy, Eo so min energy needed is 2Eo for there to be enough energy to produce particles (energy conserved)
- So, Emin = 2Eo
What is rest energy?
Amount of energy produced if all mass was transformed into energy
What happens if a photon has enough energy?
Can produce electron-positron pair. This happens when a photon passes near the nucleus
Why does particles produced in a detector curve away from each other in opposite directions?
Because they are in an applied magnetic field and have opposite charges
Why is a electron-positron pair usually produced in pair production?
Because they have a low mass which means a low rest energy is needed for pair production to occur
What can hadrons feel and leptons cant?
the strong nuclear force
What are hadrons made of?
Quarks (they arent fundamental particles)
What are the 2 types of hadrons?
Baryons and Mesons
What is the only stable baryon?
Proton (all others usually decay to protons)
Why dont you find antibaryons?
They are usually annihilated as soon as they are formed
What is baryon number?
Number of baryons (has to be conserved)
Proton = +1, Antiproton = -1 etc
What do mesons interact with baryons via?
The Strong nuclear force
What are mesons?
- They are a type of hadron that are unstable (baryon number = 0)
- They have 2 quarks
- found in cosmic showers
What are the 2 types of mesons?
Pions and kaons
Pions?
- lightest meson
- Can have +, - or 0
- They are the exchange particle of the SNF
Kaons?
- Heavier and more unstable
- can have +, - or 0
- Shorter lifetime than pions
- Have 2 quarks one of which is a strange quark
how can you detect mesons?
Use 2 geiger counters separated by absorbing lead, if they both detect at same time = cosmic ray shower
What do leptons react via?
Weak interaction (with a bit of gravitational/electromagnetic)
What are muons?
heavy electrons that are unstable and decay to normal electrons
What do electrons and muons have?
There own neutrinos (electron neutrino and muon neutrino) - have lepton number of +1
What are strange particles created in?
Strong interaction (strangeness has to be conserved, so they’re created in pairs)
What is the strangeness of leptons?
0
What do strange particles decay via?
The weak interaction (strangeness not conserved in weak)
What properties are conserved in all interactions?
Momentum, energy, charge, baryon number, lepton number, strangeness (except not always conserved in weak)
When can type of quarks change?
in weak interaction
Baryon quark structure?
qqq
Quark confinement?
Can’t get a quark on its own even if energy is applied
Quark structure of mesons?
Quark and an antiquark (kaons have a strange quark)
Beta minus decay and quarks?
Neutron to proton ( down to up - weak interaction )
Beta plus and quarks?
Proton to a neutron (up to down)
What is an exchange particle?
Virtual particle which allows forces to act in a particle interaction ( determines a forces range, heavier = shorter )
Why does the weak interaction have a short range?
W boson is heavier than a proton
Exchange particle of strong interaction?
Pion (hadrons affected)
Exchange particle of Electromagnetic?
Virtual photon (these have 0 mass so infinite range)
Exchange particle of weak interaction?
W+/W- boson
Electron capture and electron-proton collision?
Same equation ( p + e- --> n + electron neutrino) but different particle acting Electron capture = w+ Electron proton collision = w-
Feynman diagrams
Exchange particle always comes from the particle that is acting
