Particles & radiation Flashcards
What is the specific charge of a particle?
charge-mass ratio
What are isotopes?
Atoms with the same number of protons but different number of neutrons.
What is the strong nuclear force?
keeps the nuclei stable by counteracting the electrostatic force of repulsion between protons in the nucleus.
What is the range of strong nuclear force?
-attractive up to 3fm
-repulsive below 0.5 fm
What happens to the numbers in alpha decay?
-proton number decreases by 2
-nucleon number decreases by 4
What is beta-minus decay?
Beta minus decay occurs in nuclei which are neutron-rich.
What happens to the numbers in beta minus decay?
-proton number increases by 1
-nucleon number stays the same.
What are photons?
EM radiation that travels in packets which transfer energy and have no mass.
What is the equation of the energy of a photon?
E=hf
What is Planck’s constant (h)?
6.63^10^-34
What is annihilation?
It is where a particle and its corresponding anti-particle collide and their masses are converted into energy.
-Energy (including KE of particles) is released in the form of two photons which travel in opposite directions.
Why do the photons travel in opposite directions in annihilation?
To conserve momentum?
Give one example of annihilation as an application?
PET scanner- introduce positron emitting radioisotope into patient where positrons are released and annihilate with electrons that are already in the patient, which emit gamma photons which can easily be detected.
What is pair production?
Where a photon is converted into matter and its corresponding anti-matter
What is the condition that pair production must occur in?
Energy of photon>total rest energy of both particles
What happens to the excess energy from pair production?
Any excess energy is converted into kinetic energy of the particles.
What force is responsible for beta plus decay?
Weak force
What force is responsible for beta minus decay?
Weak force
What is the general equation for beta-minus decay?
n–p+beta minus particle+anti-neutrino
What is the general equation for beta-plus decay?
p–n+beta plus particle+neutrino
What do unstable particles do?
They emit a particle and break down into a new nucleus and the nucleus transitions to a lower energy state to become more stable
What are the 4 fundamental forces?
gravity, electromagnetic, strong nuclear force, weak nuclear force
What are exchange particles?
They carry energy and momentum between particles
What is the exchange particle for a SNF?
gluon
What is the range of SNF?
3^10^-15m
What does SNF act on?
Hadrons
What is the exchange particle for weak force?
W boson (+/-)
What is the range of the weak force?
10^-18m
What does the weak force act on?
All particles.
What is the exchange particle for electromagnetic force?
Virtual photon
What is the range of the electromagnetic force?
Infinite
What does the electromagnetic force act on?
charged particles
What is the exchange particle for gravity?
Graviton
What is the range for gravity?
Infinite
What does gravity act on?
Particles with mass.
What is responsible for electron capture and electron-proton collision?
Weak nuclear force
What is the equation for electron capture and electron proton collision?
e^-+p–>n+Ve
electron+proton–>neutron+neutrino
What is difference between electron-proton collision and electron capture?
Electron-proton uses W^- exchange particle whereas electron capture uses W^+ exchange particle
What is a fundamental particle?
They are particles that cannot be broken down into smaller particles and do not experience the SNF.
What is the difference between hadrons and leptons?
Leptons are fundamental particles and hadrons are not.
What are hadrons split into?
Baryons, anti-baryons and mesons.
What is a baryon made up of?
Made from three quarks
What is the quark make-up of a proton?
uud
What is the quark make-up of a neutron?
udd
What is the only stable baryon?
Proton- therefore all other baryons will eventually decay into a proton
Which are heavier–> baryons and mesons or leptons?
baryons and mesons are heavier than leptons
What are the 6 leptons?
-electron
-electron neutrino
-muon
-muon neutrino
-tauon
-tauon neutrino
What is the lepton number for the 6 leptons?
+1
What is the charge for any neutrino?
0
What conservation laws must be obeyed for particle interactions to take place?
-charge
-baryon no
-lepton no
-strangeness
What doesn’t have to be conserved in weak interactions?
strangeness
What must have a strangeness of zero?
leptons
How were muons discovered?
through the study of cosmic rays
What is an electron’s anti-particle?
positron
What do muons decay into?
electron
How are strange particles produced and how do they decay?
Strange particles are produced via SN interaction but decay via the weak interaction.
What do kaons decay into?
Pions, via the weak interaction.
What are quarks?
Quarks are fundamental particles which make up hadrons.
What are the 6 different quarks?
-up
-down
-strange
-charm
-top
-bottom
What is the standard model?
It describes the fundamental particles & 3/4 fundamental forces that exist (not gravity).
-classifies ALL known particles.
What is the photoelectric effect?
It is where photoelectrons are emitted from the surface of a metal after light above the threshold frequency is shone on it
What is the threshold frequency?
The lowest frequency of light that has enough energy to emit photoelectrons.
What is the work function?
It is the minimum energy required for electrons to be emitted from the surface
What’s the difference between UV and visible light?
UV has a higher frequency hence more energy
How can an electron gain energy to reach the work function?
Electrons can be given the energy through photons because when a photon collides with an electron it transfers all its energy to the electron.
What happens if a photon has more energy than the work function?
The electron ionises and escapes but any excess energy is converted into the photoelectron’s KE.
What happens if the photon has less energy than the work function?
The electron will not be able to ionise and escape but it may be excited to a higher energy level.
What is the difference between electrons closer/further away from the metal surface?
Electrons closer to the metal surface will need less energy to escape than those deeper in the metal.
What does increasing the intensity of the radiation incident on a metal surface do?
It increases the number of electrons emitted per second
- Increasing intensity=more photons bring emitted every second.
-hence more photons are hitting the surface of the metal hence more electrons are knocked off every second.
What is max KE of emitted electrons dependent on/independent of?
Dependent on frequency
Independent of intensity
-More energy photon has, more it can transfer to the photoelectron as KE.
What would the wave theory expect of the photoelectric effect?
-the trapped electrons would keep gaining energy from light as if it was acting as a wave-longer the light was shone, the more energy electron would gain.
-therefore low intensity/low frequency light would still eject electrons but would just take longer
-THIS HOWEVER DOESN’T HAPPEN SO WAVE THEORY IS WRONG!
