3.2.1 Particles Flashcards
What force keeps the nucleus stable?
Strong nuclear force
What is the range of strong nuclear force at which it is; repulsive, attractive and COMPLETELY ineffective
Below 0.5fm, between 0.5-3fm, above 3fm
Why was the neutrino first hypothesised?
and what is it?
.To account for the change in energy during beta decay
.It is a particle with no mass or charge but has KE therefore conserving energy
Describe pair production
a gamma photon with sufficient energy(roughly 2x the rest energy of the particle it’s trying to pair produce) is near the nucleus.
This creates a particle and its antiparticle (to conserve charge) dependant on the energy of the photon.
Any excess energy is converted to KE and distributed evenly
What is required for alpha decay to occur?
And why is this required?
.The nucleus must be large e.g. radium
.This is required so that the SNF can’t keep the nucleus stable
What is required for beta minus decay?
And why is this required?
.The nucleus must be neutron rich
.this is so that a neutron can change into a proton
What is emitted in alpha decay?
A helium nucleus
/
2 protons and 2 neutrons
What happens in beta decay?
A neutron changes into a proton
An electron is emitted from the nucleus
An electron anti-neutrino is also emitted
What are the two types of neutrinos?
Electron neutrino
Muon neutrino
What is needed for gamma decay to occur?
A nucleus with excess energy(normally after alpha or beta decay)
What are gamma rays made of?
High energy EM waves that don’t change the nucleus at all
What is the anti particle of:
Proton, electron, neutron, neutrino
Antiproton, positron, antineutron, antineutrino
What can EM radiation behave as?
A wave or a particle
Known as wave particle duality
Define a photon
A packet of EM radiation with no mass or charge
Antiparticle and particle (opposite or same):
Mass
Charge
Rest energy
Same
Opposite
Same
Describe one application of annihilation
PET scanners
Used in medicine to detect cancerous tumours as if you inject a tracer that emits positrons annihilation will occur with the electrons found naturally in the body. Cancer cells will absorb this tracer at a faster rate and so this area will emit more photons as a result of annihilation. Therefore the location of the tumour can be detected by scamners
What are the four fundamental forces?
Strong nuclear force, gravity, electromagnetic force, weak nuclear force)
What are the 2 requirements for particle interaction?
One of the four fundamental forces
An exchange particle
What is the other name for an exchange particle?
Gauge boson
What is an exchange particles purpose?
It moves between two particles using momentum and so gives rise to a force between the particles.
What is the ;exchange particle, particles affected, range and strength of strong nuclear force
Virtual Pions,hadrons,10 to the -15m, strongest
What is the exchange particle, particles affected ,range and strength of electromagnetic force?
Virtual photon (y), any with a charge, infinite, 2nd strongest
What is the exchange particle, particles affected ,range and strength of weak nuclear force?
W+ and W- bosons, everything, 10^-18m, 3rd strongest
What is the exchange particle, particles affected ,range and strength of gravity?
Graviton(theoretical), any with mass, infinite, weakest
What is the rule of mass and range for exchange particles
The larger the mass the shorter the range
(Inversely proportional)
What is the Feynman diagram for beta minus decay?
Click me link
What is the Feynman diagram for beta plus decay?
Click me link
What is the Feynman diagram for electron capture?
Click me link
What is the Feynman diagram for electron-proton collisions?
Click me link
What are leptons key characteristics
They don’t experience snf
They are fundamental particles
Name 2 leptons
Electrons
Muons
What are the key characteristics of hadrons
They experience snf
They are made up of quarks
What defines the sub groups of hadrons
Baryons have 3 quarks
Mesons have a quark antiquark pair
Name 2 baryons
Protons
Neutrons
Name 2 mesons
Pions
Kaons
What must be conserved in particle interactions?
Baryon number
Lepton number
Strangeness (only in strong nuclear interactions)
Charge
Energy
Momentum
Why do kaons have a strange property and what does this cause
They have a longer lifetime than expected
This causes them to only be produced in pairs of strange particles
How can strangeness change in weak interactions?
-1, 0, +1
How much mass and charge do neutrinos have?
Zero or almost zero
Zero
What are the three types of quarks (excluding antiquarks)
Up, down and strange
Which quark has greater mass
Strange and anti strange quarks
What is the quark composition of a proton?
UUD
What is the quark composition of a neutron?
UDD
What is the quark composition of a pion?
U(U)
D(D)
() = anti
What is the quark composition of a kaon?
K+ u(s)
K- (u)s
K0 d(s) / (d)s
/ = or
() = anti
What is the strangeness of k+ and Ko
+1
What is the strangeness of K- and (Ko)?
() = anti
-1
How does quark character change in B+ decay?
An up quark changes into a down quark
How does quark character change in B- decay?
A down quark changes into a up quark
Describe nuclide notation
a
X
z
Where
a = nucleon number(mass number)
X = the chemical symbol of the element
z = atomic number(proton number)
Define isotopes
Atoms of the same element (defined by the number of protons) but different numbers of neutrons
Describe annihilation
When a particle meets its equivalent anti particle they are both destroyed and all their mass is converted to energy in the form of (at least) two gamma ray photons which move apart in opposite directions to conserve momentum
What does exchange particles being virtual mean?
They only exist for a short time and cannot be detected
What do all baryons eventually decay into?
Protons
What do mesons decay into?
Pions
What do leptons decay into?
Electrons
How are strange particles produced/ decay
Produced: strong interaction
Decay: weak interaction
Why does particle physics rely on large teams?
Peer review
Describe mass energy conservation
If there is a decrease in mass during an interaction there must be an increase in energy to compensate for this (and vice versa).
Why must pair production occur near the nucleus?
So that momentum is conserved by the nucleus recoiling opposite to the direction of the particle anti-particle pair.
Why must strange particles be produced in pairs?
Strange particles are produced during the strong interaction which requires the strange number to be conserved.
Therefore particles must be produced in pairs and these particles must have opposite strangeness (1/-1) to ensure strangeness remains constant throughout the reaction
Describe quark confinement
It’s impossible for quarks to exist in isolation because as you supply enough energy to split the quarks apart there would first be enough to pair produce a meson which would use up the energy making it impossible to reach the energy required to free a quark.
