Particles and Radiation Flashcards
What is specific charge?
Charge/ mass
What is an isotope?
Isotopes are atoms of the same element with different masses due to differing numbers of neutrons in their nucleus
What is the strong nuclear force?
Force only experienced by hadrons
Exchange particles are gluons
Force is responsible for keeping protons and neutrons in the nucleus together
Attractive between 0.5 and 3 Fm and repulsive under 0.5 Fm
What is Alpha decay?
Where a nucleus becomes stable by emitting an alpha particle. This consists of 2 protons and 2 neutrons
What is beta minus decay?
Where a neutron turns into a proton. It emits an electron and an antineutrino
What is beta plus decay?
Proton turns into a neutron. A positron and neutrino are emitted
How was the existence of the neutrino hypothesised? Why is it needed?
Neutrino has no charge and negligible mass
Its existence was hypothesised to account in order to account for the conservation of energy in beta decay
Beta particles have a continuous range of energies. This is because the energy released in beta decay is shared between the beta particles (electron/ position) and the neutrino. There is a fixed amount of total energy for the decay, so the energy difference must be carried away by another particle
What is a photon?
Fundamental particles that make up all forms of electromagnetic radiation
Photon is a mass less packet of electromagnetic energy
This means that energy is not transferred continuously but as discrete packets of energy
What happens when a matter and anti-matter collide?
They annihilate each other to produce 2 photons which travel in opposite directions, in order to conserve momentum
What are the four fundamental interactions?
gravity-
electromagnetic
strong nuclear
weak nuclear
What are exchange particles?
When forces interact between two bodies, an exchange particle is passed between them. The exchange particle acts as the force carrier. It exists only for a few moments
Describe the electromagnetic force
Acts on particle with charge. Infinite range. Virtual photons are the exchange particle.
Describe the weak interaction
Limited to Beta plus/minus decay, electron capture and proton-electron collisions. W+ and W- bosons. Range 10*-18m
Describe the strong interaction
Only affects hadrons. Pion is the exchange particle
What are the two classes of hadrons? Give examples of each
Baryons- proton/neutron, and Anti-baryons (anti-proton/ anti neutron)
Mesons- pion, kaon
What do all baryons decay into?
Proton
What must be conserved in interactions?
Baryon number
Charge
Electron lepton number and muon lepton number
Energy and Momentum
Strangeness must be conserved in strong interactions, but can change by -1,0,+1 in weak interactions
What do kaons decay into?
Pions
Lepton examples
electrons, muons, neutrinos and their antiparticles
Describe strange particles
Strangeness occurs if a particle contains a strange quark and is there to reflect strange particles are always produced in pairs.
Strange particles are produced through the strong interaction and decay through the weak interaction
How to neutrons decay?
neutron to a proton, also produces electron and anti-neutrino
Change of quark character in beta minus/plus decay
beta minus- down to up
beta plus- up to down
What is the threshold frequency?
The minimum frequency of incident electromagnetic radiation required to remove a photoelectron from the surface of a metal.
What is the work function?
The minimum amount of energy needed for an electron to be emitted
What is the stopping potential?
The p.d. required to stop photoelectric emission from occurring. KeMax= eVs
What is ionisation?
When an electron gains enough energy to be removed from the atom
What is excitation?
When an electron moves to a higher energy level. This could be caused by:
Absorbing energy from collisions with other atoms/electrons
Absorbing a photon
A physical source, such as heat
Explain how fluorescent tubes work?
A beam of electron flows from one end to another
These free electrons collide with orbital electrons in the mercury atoms
The orbital electrons gain energy and are excited to a higher energy level
They then return to ground state and UV photons are released
The electrons within the phosphorus coating absorb these photons are excited, then release visible light photons when they return to a lower energy level
Line spectra
Line spectra is a phenomenon which occurs when excited atoms emit light of certain wavelengths which correspond to different colours
The emitted light can be observed as a series of coloured lines with dark spaces in between
Each element produces a unique spectra
Emission spectra
emission spectrum contains a set of discrete wavelengths, represented by coloured lines on a black background
Absorption spectra
white light passes through a cool, low pressure gas it is found that light of certain wavelengths are missing
An absorption spectrum consists of a continuous spectrum containing all the colours with dark lines at certain wavelengths
These dark lines correspond exactly to the differences in energy levels in an atom
What shows that particles have wave like properties
Electron diffraction
What shows that EM waves have particle like properties
Photoelectric effect.
How and why does the amount of diffraction change when the momentum of the particle is changed?
Using deBroglie equation, when the momentum increases, wavelength decreases. This will mean the amount of diffraction decreases, and so the concentric rings of the interference pattern are closer together. (and vice versa)
