Particles Flashcards
What are the three constituents of the atom?
Protons, neutrons and electrons
How do you calculate specific change?
Charge/Mass
What is the symbol for proton number?
Z
What is the symbol for atomic number?
A
What is the definition of an isotope?
Atoms with the same number of protons but different number of neutrons
What is carbon dating?
calculating the percentage of carbon-14 remaining in the object and using the known starting value of carbon-14 and its half life to calculate its age
What is the strong nuclear force?
Keeps nuclei stable by counteracting the electrostatic force of repulsion between protons in the nucleus.
What are the only constituent of the atom that experience the strong nuclear force?
Nucleons
What is the range of the strong nuclear force?
Attractive up to 3fm but repulsive below 0.5fm
What is an unstable nucleus
A nucleus with too many protons, neutrons or both causing the strong nuclear force to not be enough to keep them stable therefore they will decay
When does alpha decay occur?
In large nuclei with too many of both protons and neutrons
What changes occur after alpha decay?
-2 protons -2 neutrons
When does Beta minus decay occur?
In a neutron rich nucleus
Why did physicists hypothesise neutrinos?
Because after beta-minus decay the energy levels before and after showed that energy was not conserved and energy has to be observed so therefore they hypothesised neutrinos
Compare a particle and its antiparticle
Same mass, same magnitude of change but opposite charge
How does electromagnetic radiation travel?
In packets called photons which transfer energy and have no mass
What is te energy of photons directly proportional to?
The frequency of electromagnetic radiation
What is Annihilation?
When a particle and its antiparticle collide and as a result their masses are converted into energy.
How is the energy from annihilation released?
In the form of 2 photons that move in opposite directions (to conserve momentum) and kinetic energy
How can annihilation be used for medical imaging?
In PET scanners by introducing positron emitting radioisotopes into the patelence and these positrons annihilate with electrons already in their system emitting gamma photons which can be detected to produce and image
What is pair production?
when a photon is converted into an equal amount of matter and antimatter.
When can pair production occur?
When the photon has an energy greater than the energy of both particles. Any excess is converted to kinetic energy
What are the four fundamental forces?
Gravity, electromagnetic, strong nuclear and weak nuclear
How are forced between particles caused?
Exchange particles
What are exchange particles?
They carry momentum between the particles experiencing the force
What is the exchange particle for the strong force?
Gluon/pion
What is the exchange particle for the weak nuclear force?
W+ and W- bosons
What is the exchange particle for the electromagnetic force?
The virtual photon
What does the weak nuclear force act on?
All particles
What does the electromagnetic force act on?
Charged particles
What particles does Gravity act on?
Particles with mass
What is the range of the electromagnetic force?
Infinite
What is the range of gravity?
Infinite
What is the range of the strong nuclear force?
3fm
What is the range of the weak nuclear force?
10^-18
What is the equation for electron capture? And what is the exchange particle?
P+ e- ~> n+ Ve
W+ boson
What is the equation for electron-proton collision? And what is the exchange particle?
P+ e- ~> n +Ve
W- boson
What is the equation for beta-plus decay? And what is the exchange particle?
p ~> n+e+ +Ve
W+ boson
What is the equation for beta-minus decay? And what is the exchange particle?
__
n ~> p+ e- + Ve
W-boson
What are leptons?
Fundamental particles which means they can’t be broken down even more and do not experience the strong nuclear force
What are hadrons?
particles made of quarks (which are fundamental) that experience the strong force
What is a baryon?
Something made up of 3 quarks
What is a meson?
A particle made up of a quark and an antiquark?
Name some mesons?
Pions, kaons
What is the baryon number of a baryon?
+1
Is baryon number conserved in interactions?
Yes
What is the only stable baryon?
The proton
All baryons will eventually decay into a proton
What is the lepton number of a lepton?
+1
Is lepton number conserved in interactions?
Yes
What is a muon?
A lepton which decays into electrons
What are strange particles?
Kaons which decay to pions. Particles which are produced by the strong nuclear nuclear interaction but decay by the weak interaction.
What is strangeness?
A property of particles which show that strange particles must be created in pairs as strangeness must be conserved in strong interactions.
Does strangeness have to be conserved?
Yes in strong interactions
And not necessarily in weak interactions
Why does particle physics need international collaboration?
Particle accelerators are very expensive and it produces huge amounts of data and evidence must be peer-reviewed by a community
What is the quark combination and strangeness of a neutral pion?
_ _
uu or dd
strangeness=0
What is the quark combination and strangeness of a positive pion?
_
ud
Strangeness =0
What is the quark combination and strangeness of a negative pion?
_
ud
Strangeness=0
What is the quark combination and strangeness of a neutral kaon?
_ _
ds or ds
Strangeness=+1 or -1
What is the quark combination and strangeness of a positive kaon?
_
us
Strangeness=+1
What is the quark combination and strangeness of a negative kaon?
_
us
Strangeness=-1
What properties must always be conserved in particle interactions?
- Energy and Momentum
- Charge
- Baryon number
- Lepton number
What interaction does beta decay occur by?
Weak as there is a change of quark type
What is the photoelectric effect?
When photoelectrons are emitted from the surface of a metal after light above a certain frequency is shone on it.
What is the threshold frequency of a metal?
The minimum frequency required for photoelectrons to be emitted
Why is there a threshold frequency?
Because each electron can absorb a single photon therefore a photoelectron is only emitted if the frequency is above the threshold frequency
What happens when you increase the intensity of the light that it incident on the metal?
More photoelectrons are emitted
What happens when you increase the frequency of the incident light?
The photoelectrons have more kinetic energy
What is the work function?
The minumum energy required for electrons to be emitted from the surface of a metal
What is the stopping potential?
The potential difference you would need to apply across the metal to stop the photoelectrons with the maximum kinetic energy
How can you use stopping potential to find the maximum kinetic energy of the released photoelectrons?
Stopping potential x charge of an electron
Where do electrons exist?
In discrete energy levels (quantised)
What is excitation?
When electrons gain energy from collisions with free electrons which cause them to move up an energy level
What is ionisation?
When electrons gain so much energy from collisions with free electrons that they can be removed from the atom entirely. This only occurs when the energy of the free electron is greater than the ionisation energy.
What is de-excitation?
when an electron becomes excited it will quickly return to its original energy level (ground state) and release the energy it gained in the form of the photon
What happens in a fluorescent tube?
It is filled with mercury vapour, across which a high voltage is applied. This voltage accelerates free electrons through the tube, which collide with the mercury atoms causing them to be ionised, releasing more free electrons. The free electrons collide with mercury atoms causing them to become excited. when they de-excite they release UV photons which are absorbed by fluorescent coating on the inside of the tube. The electrons in the coating therefore become excited and de-excite to produce visible light.
What is an electron volt?
The energy gained by one electron when passing through a potential difference of 1 volt
How do you get a line spectrum and what does each line represent?
You create one by passing light from a fluorescent tube through a diffraction grating or prism. Each line in the spectrum represents a different wavelength of light emitted by the tube.
Is a light spectrum continuous or non-continuous?
Non continuous as it contains discrete values of the wavelength.
How do we know electrons can only transition between discrete energy levels?
As the only photon energies emitted will correspond to the wavelengths shown on the line spectrum
How do you get a line absorption spectrum?
By passing white light through a cooled gas
What does an absorption spectrum look like?
A continuous spectrum with black lines at certain wavelengths.
What do the black lines in an absorption spectrum represent?
The possible differences in energy levels as the atoms in the gas can only absorb photons of an energy equal to the exact difference between two energy levels.
What experiments show the wave nature of light?
Diffraction and interference
What experiments show the particle nature of light?
The photoelectric effect
What experiment shows that electrons have a wavelength?
Electron diffraction
