Chapter 1: Particle Physics Flashcards
What are the three forces acting on the nucleons in the nucleus?
- electrostatic repulsion of +ve protons
- strong nuclear force- attractive force that holds the nucleus together
- gravitational force-causes all nucleons to attract to each other due to their masses (but its a lot weaker than electrostatic forces)
What is the strong nuclear force?
a force that acts on all nucleons that is attractive up to a range of 3fm and repulsive below a range of about (0.5fm), it is responsible for the stability of a nucleus
(overcomes the electrostatic repulsion of protons)
What is the shape of a graph to represent strong nuclear force?
-maximum attractive force is at 1fm
-force becomes 0 at 3fm
-until 0.5fm, repulsion is never zero because no two masses can ever be in the exact same place in the universe
(should be able to draw graph and with a comparison for electrostatic force!!!!!!!!!!!)
What is the range for the strong nuclear forces?
attractive - up to 3fm
repulsion - below 0.5fm
What is nuclear decay?
when unstable nuclei emit particles to become more stable
From what type of particles are alpha particles decayed from?
large nuclei because they are too big for the strong nuclear force to keep them stable
too many protons/neutrons/both
What is alpha decay and what is its formula?
-helium nucleus (2 protons and 2 neutrons)
ᴬzX——- ᴬ-⁴z-₂X + ⁴₂α
In what type of particles does beta decay occur?
nuclei with too many neutrons
What is beta-minus decay?
emission of an electron with an antineutrino
a neutron turns into a proton and an electron is emitted
antineutrino particle carries away some energy and momentum
What is the formula for beta-minus decay?
ᵃzX——–> ᵃz+₁W + ⁰₁β + ̅νe
What is beta plus decay?
a proton turns into a neutron and a positron and an electron neutrino are released
What is frequency?
the number of complete waves that pass a point per second
What is wavelength?
the distance between two adjacent crests of a wave
What is the EM spectrum
longest wavelength—shortest wavelength
radio waves micro-waves infrared visible light ultraviolet X-rays gamma rays
What is a photon?
a packet of EM radiation that has a specific (discrete) amount of energy, it transfers energy and has no mass
What is the formula for the speed of light?
c = f * λ
c=3x10⁸
What is the formula for photon energy? (two versions)
E= h * f or E= h*c/λ
What is h?
planck’s constant
6.63x10⁻³⁴
What can a beam of photons be related to?
a beam of photons can be related to generating a POWER
What is the formula for power (in terms of photons)
P=nhf
n=number of photons per second
P=power-W
What is an electron volt?
an eV is the energy required to increase an electron’s energy through one volt (V=E/Q)
energy in joules = charge of an e⁻ x 1V
What is 1 eV and 1 Mev in Joules?
1 eV=1.6x10⁻¹⁹J
1 MeV= 1.6x10⁻¹³J
What is antimatter and three properties?
a particle that has opposite properties to its corresponding matter
- same rest mass and rest energy
- has opposite charge
- will destroy its counterpart
What is annihilation?
when a particle meets its corresponding antiparticle, ALL of the matter is converted to two gamma ray PHOTONS that move in opposite directions to conserve momentum (draw the diagram)
Describe the way photons travel after annihilation?
they move in opposite directions and perpendicular to matter/antimatter to conserve momentum
What is pair production?
when energy is converted into mass, then you get equal amounts of matter and antimatter
it always produces a particle and its corresponding antiparticle
What condition is required for pair production to occur?
it only happens if there is enough energy to produce the masses of the particles
What is the minimum energy required for pair production?
the total rest energies of the particles that are produced
Eₘᵢₙ=2E₀
E₀ is the rest energy of particle type produced
What is usually produced from pair production?
electron-positron pairs
because they have relatively low mass
low mass means low rest energy so less energy is required for the pair production to happen
What is an example of an isotope and how is it used?
Carbon-14 (radioactive isotope)
It can be used to find the approx. age of an object containing organic material. You calculate the % of C-14 in the object and using the known starting value of carbon (which is the same for all living things) and its half-life to calculate its approx. age
Why do nuclei decay to become more stable?
they decay to emit radiation because they have too many protons/neutrons which causes the SNF to not be strong enough to keep them stable
How were neutrinos discovered?
they were first hypothesised because when analysing the energy levels of the particles before and after beta minus decay, they were not the same, so the neutrino was hypothesised to make up for that difference in energy, then they were later discovered
What is a neutrino?
it is a lepton with no charge and (almost) zero mass
What is the value of planck’s constant and the speed of light?
- 63 x 10⁻³⁴ Js =h
3. 00 x 10⁸ ms⁻¹ = c
If photon has more than twice the rest energy of a particle during pair production, then what happens to the remaining energy?
it is used as kinetic energy of the particles
What are the 4 fundamental forces?
gravity
electromagnetic
strong nuclear force
weak nuclear force
What are exchange particles?
particles that carry momentum and energy between particles experiencing a force
(forces between particles are caused by exchange particles)
What is the analogy for describing repulsion?
two people on an ice-rink throwing a heavy ball (facing each other)
as the ball is being thrown, it carries momentum which causes the 2nd person to move back
What is the analogy for describing attraction?
two people on an ice-rink facing away from each other and one throws a boomerang
the boomerang carries momentum to the other person and pushes them both closer together
What is the exchange particle for the strong nuclear force and its range ?
What particles does the SNF act on?
exchange particle: gluon
range: 3 x 10⁻¹⁵m
acts on: hadrons
What is the exchange particle for the weak nuclear force and its range ?
What particles does the WNF act on?
exchange particle: W boson (W⁺ or W⁻)
range: 10⁻¹⁸m
acts on: all particle
What is the exchange particle for electromagnetism and its range ?
What particles does electromagnetism act on?
exchange particle: virtual photon (γ)
range: infinite
acts on: all charged particles
What is the exchange particle for gravity and its range?
What particles does gravity act on?
exchange particle: graviton (but its not on the spec)
range: infinite
acts on: all particles that have a mass
What interactions is the weak nuclear force responsible for? (3)
- beta decay
- electron capture
- electron-proton collisions
What is electron capture (and draw its Feynman diagram)?
when a nucleus captures one of the orbiting electrons and a proton changes into a neutron
Feynman diagram: W+ boson (from proton to neutron/ left to right)
proton and electron at bottom
neutron and neutrino at top (respectively)
What is the general term for an exchange particle?
boson
Draw the Feynman diagram for beta minus decay?
neutron at bottom
proton on top
W- boson
e and antineutrino on right top
What 2 categories can all particles be placed in?
hadrons and leptons
What are leptons?
List 3 examples
they are a type of fundamental particle
does NOT experience strong force
e.g- electrons and neutrinos and muons
What does it mean to be a fundamental particle?
cannot be broken down into anything smaller
What are hadrons?
List 4 examples
- are made up of quarks (not fundamental particles)
- experience the strong nuclear force
- this group can be further divided into baryons or anti baryons or mesons
e. g- protons, neutrons, pions, kaons
What are baryons?
- made up of 3 quarks/antiquarks
- decays into protons
- protons, neutrons
What are mesons?
- made up of a quark and antiquark
- does not decay into a proton
- e.g- pion, kaon
What are baryon numbers?
it is a property of a particle that shows whether it is a baryon (1) or an antibaryon (-1) or not a baryon at all (0)
the baryon number is always CONSERVED in particle interactions
What is the only stable baryon and what happens to the other particles?
a proton
all other baryons eventually decay into a proton
What is are lepton numbers?
shows whether a particle is a lepton (1), an antilepton (-1) or not a lepton at all (0)
lepton numbers are always CONSERVED in particle interactions
2 types of lepton numbers: electron neutrino, muon neutrino
What are the two types of lepton numbers?
electron lepton numbers
muon lepton numbers
What is a muon?
it is a lepton, a heavy electron
-1 charge but x200 the mass of an electron
they decay into electrons
What are strange particles and an example?
they are produced by the strong force but they decay by the weak interaction
e.g- kaons
What is strangeness?
a property of particles
strange particles must be produced in pairs
strangeness is conserved in strong interactions
in weak interactions, strangeness can change by 0, +1 or -1
How can particles be investigated?
cloud chambers particle accelerators (but they are very expensive)
Draw the Feynman diagram for:
- beta minus decay
- beta plus decay
- electron capture
- electrostatic repulsion
- electron-proton collision
see wall for answers 5. proton (bottom left) electron (bottom right) exchange particle= W- neutron= top left electron neutrino= top right
What happens to a positron straight after pair production?
it will meet its antiparticle (electron) and it will annihilate
What particle is responsible for mass?
Higgs boson
