1. Particle Physics Flashcards
What makes up an atom?
a nucleus and electrons
What makes up the nucleus?
protons and neutrons
What are protons and neutrons?
nucleons
What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
1/2000
What is the mass of a proton?
1.67 x 10^-27 kg
What is the mass of a neutron?
1.67 x 10^-27 kg
What is the mass of an electron?
9.11 x 10^-31 kg
What is the relative charge of a proton?
+1
What is the relative charge of a neutron?
0
What is the relative charge of an electron?
-1
What is the charge of a proton?
+1.60 x 10^-19 C
What is the charge of a neutron?
0 C
What is the charge of an electron?
-1.60 x 10^-19 C
What is nuclide notation?
how information on elements is displayed on the periodic table
What is an isotope?
at atom with the same number of protons but a different number of neutrons
What happens when you change the number of protons in an atom?
create a new element
What happens when you change the number of neutrons in an atom?
create an isotope
What happens when you change the number of electrons in an atom?
create a new ion
What does isotopic data mean?
the relative amounts of the different isotopes of an element present in a substance
What happens to unstable nuclei over time?
they decay into more stable nuclei over time
How can you estimate a material’s age?
by looking at the amount of isotopes in the material
What is specific charge?
the amount of charge an object has per kilogram
What three things could you be asked to find the specific charge of?
- a single particle
- a nucleus
- an ion
How do you calculate the specific charge?
total charge/total mass
What is specific charge measured in?
Ckg^-1
What is meant by the relative mass of an atomic constituent?
relative mass is the mass relative to a proton’s mass, as opposed to the actual mass
In nuclide notation, what does ‘A’ represent?
nucleon number
In nuclide notation, what does ‘Z’ represent?
proton number
In nuclide notation, what does ‘X’ represent?
element symbol
What does isotopic data mean?
the relative amounts of the different isotopes of an element present in a substance
What are the four fundamental forces?
- gravity
- electromagnetic
- strong nuclear
- weak nuclear
Outline gravity
all objects with mass are attracted to each other
Outline the electromagnetic force
all objects with charge are either attracted to or repelled from each other
Outline the strong nuclear force
responsible for holding the nucleus of atoms together and responsible for the decay and creation of particles
Outline the weak nuclear force
responsible for the decay and creation of particles
What is the name of the force that holds nucleons together inside the nucleus?
strong nuclear force
Why must the strong nuclear force exist?
the repulsion of protons due to the electromagnetic force is much greater than the gravitational attraction, so there must be another attractive force to hold the nucleus together
Which particles does the strong nuclear force affect?
both nucleons (protons and neutrons)
What type of force is the SNF?
can either be attractive or repulsive
What does the type of SNF depend on?
distance between particles
What range does the SNF have?
very short range
When is the SNF repulsive?
if nucleons are 0-0.5fm apart
When is the SNF attractive?
if nucleons are 0.5-3fm apart
When does the SNF have no effect?
if nucleons are beyond 3fm apart
Why do nuclei emit alpha and beta particles?
because they are unstable
What are the three main reasons for a nucleus being unstable?
- too much mass
- imbalance of protons and neutrons
- too much energy
How can a nucleus with too much mass become more stable? What is this called?
eject some particles (alpha decay)
How can a nucleus with an imbalance of nucleons become more stable? What is this called?
weak nuclear force can change the particle type (beta +/- decay)
How can a nucleus with too much energy become more stable? What is this called?
release some energy (gamma decay)
What is an alpha particle?
2 protons and 2 neutrons (helium nucleus)
When is an alpha particle emitted?
when a particle undergoes alpha decay
In what type of nucleus does alpha decay usually occur?
very heavy nuclei
What is the proton number of an alpha particle?
2
What is the nucleon number of an alpha particle?
4
In what type of nucleus does beta-minus decay usually occur?
neutron-rich
What happens during beta-minus decay?
a neutron turns into a proton via the weak nuclear force, emitting a beta-minus particle and an anti-neutrino
Which particle is a beta-minus particle identical to?
electron
Name three pieces of equipment which could be used to detect alpha and beta radiation
- geiger counter
- spark counter
- cloud chamber
How did observations of beta-minus decay lead to the prediction of the neutrino?
- the total energy of the particles emitted in beta-minus decay was less than the energy before
- this energy couldn’t be accounted for by the recoil of the nucleus
- therefore there must be another particle carrying away the missing energy
What are photons?
described as ‘packets’ of electromagnetic waves
What are the similarities and differences between photons?
they can have different frequencies, wavelengths and energies, but they all travel at the speed of light
What is the speed of light?
3.00 x 10^8 m/s
How is the energy of a photon related to its frequency?
directly proportional
What is the value of Planck’s constant?
6.63 x 10^-34 (m^2kg/s)
State the equation linking energy of photons (E), Planck’s constant (h) and frequency (f)?
E = hf
State the equation linking the energy of photons (E), Planck’s constant (h), speed of light (c) and wavelength (λ)?
E = (hc)/λ
What is annihilation?
when a particle and its corresponding antiparticle meet and their mass (and kinetic energy) is converted into two photons, travelling in opposite directions to conserve momentum
What is pair production?
when a photon with enough energy converts its energy into a particle and its corresponding antiparticle pair
What is anti-matter?
particles which have identical mass as their corresponding matter particle, but every other property is opposite
What is the charge and mass of a proton?
- charge: +1.60 x 10^-19 C
- mass: 1.67 x 10^-27 kg
What is the charge and mass of an anti-proton?
- charge: -1.60 x 10^-19 C
- mass: 1.67 x 10^-27 kg
What is the charge and mass of a neutron?
- charge: 0 C
- mass: 1.67 x 10^-27 kg
What is the charge and mass of an anti-neutron?
- charge: 0 C
- mass: 1.67 x 10^-27 kg
What is the charge and mass of an electron?
- charge: -1.60 x 10^-19 C
- mass: 9.11 x 10^-31 kg
What is the charge and mass of a positron?
- charge: +1.60 x 10^-19 C
- mass: 9.11 x 10^-31 kg
What unit is used to measure energy at this scale?
electron volt (eV)
What is an electron volt?
the kinetic energy gained by an electron if it passes through a potential difference of 1V
What is 1 eV in Joules?
1.60 x 10^-19 J
What is 1 MeV in Joules?
1.60 x 10^-13 J
What is rest energy?
the energy stored in an objects mass
What is the rest energy of a proton and an anti-proton?
938.257 MeV
What is the rest energy of a neutron and an anti-neutron?
939.511 MeV
What is the rest energy of an electron and a positron?
0.511 MeV
What is energy released as during annihilation?
two identical photons
Why are the photons emitted in opposite directions during annihilation?
to conserve momentum
What does E0 stand for?
rest energy
What does Emin stand for?
energy of photon
In pair production, what can be produced when you have a more energetic photon?
- heavier particles
- particles with extra kinetic energy
- lots of smaller particles
What formula is used to calculate the energy released in annihilation?
E0 = Emin
What formula is used to calculate the energy needed for pair production?
2E0 = Emin
What are the four main groups of particles?
- hadrons
- leptons
- baryons
- mesons
What are the two main groups of all matter and anti-matter?
hadrons and leptons
What is a hadron?
a particle which experiences the strong nuclear force and can be broken up into smaller particles (quarks)
What is a lepton?
a type of fundamental particle which does not experience the strong nuclear force
What are the two types of hadrons?
baryons and mesons
What is the difference between a baryon and a meson?
a baryon is made up of 3 quarks whereas a meson is made up of 2 quarks
Which is the most stable baryon?
proton
Which baryon will all baryons eventually decay into?
proton
State three examples of baryons
- protons
- neutrons
- sigmas
State two examples of anti-baryons
- anti-protons
- anti-neutrons
What are quantum numbers?
fundamental properties that must always be conserved
What are the typical values of quantum numbers?
+1, 0, -1
State the four quantum numbers
- relative charge
- baryon number
- lepton electron number
- lepton muon number
What is the baryon number of a baryon?
+1
What is the baryon number of an anti-baryon?
-1
What is the baryon number of leptons and mesons?
0
Are mesons stable or unstable?
unstable
What are the two main groups of mesons?
pions and kaons
What three types of mesons are there?
positive, neutral and negative
Which forces are felt by leptons?
- gravity
- electromagnetism (if charged)
- the weak nuclear force
What is the criteria for a lepton to feel electromagnetism?
the lepton must be charged
What is a muon?
a big unstable electron, which will eventually decay into an electron
What is a neutrino?
a very low mass particle that interacts very weakly with other matter
What are the two types of quantum number that a lepton may have?
- lepton electron number
- lepton muon number
What are the only values of both types of lepton number?
+1, 0, -1
What is the lepton electron number and lepton muon number of an electron?
- lepton electron = +1
- lepton muon = 0
What is the lepton electron number and lepton muon number of a positron?
- lepton electron = -1
- lepton muon = 0
What are the 6 mesons on the spec?
- pion plus
- pion zero
- pion minus
- kaon plus
- kaon zero
- kaon minus
What gives baryons and mesons their overall properties?
quarks and anti-quarks
What is the quark composition of a baryon?
3 quarks (qqq)
What is the quark composition of a meson?
1 quark and 1 antiquark
What is the baryon number of a quark?
+1/3
What is the baryon number of an antiquark?
-1/3
What are the 6 quarks and antiquarks on the spec?
- up
- down
- strange
- anti-up
- anti-down
- anti-strange
What is the charge of an up quark?
+2/3
What is the charge of a down quark?
-1/3
What is the charge of a strange quark?
-1/3
What is the charge of an anti-up quark?
-2/3
What is the charge of an anti-down quark?
+1/3
What is the charge of an anti-strange quark?
+1/3
What is the structure of a proton?
up, up, down
What is the structure of an anti-proton?
anti-up, anti-up, anti-down
What is the structure of a neutron?
up, down, down
What is the structure of an anti-neutron?
anti-up, anti-down, anti-down
What are the four meson rules?
- must contain a quark and an anti-quark
- the charge must add up to either +1, 0 or -1
- if the strangeness = 0, it is a pion
- if the strangeness does not = 0, it is a kaon
What is meant by the term “quark confinement”?
it is not possible to get a quark by itself
What would happen if you tried to split a meson in two? What is this called?
the amount of energy needed actually creates a quark and an anti-quark (pair production)
What three things happen when a nucleus undergoes beta minus decay?
- an electron is emitted
- an anti-electron neutrino is emitted
- a neutron turns into a proton
In a nucleus, what is responsible for a neutron turning into a proton? What is this called?
the weak nuclear force, weak interaction
What is the key difference between beta MINUS decay and beta PLUS decay?
in beta PLUS decay, a positron and a normal neutrino are produced whereas in beta MINUS decay, an electron and an anti-electron neutrino is produced
What does it mean when a property is conserved throughout an interaction?
the value of that property before is the same as the value of that property after
State six properties that are always conserved
- energy
- momentum
- charge
- baryon number
- lepton electron number
- lepton muon number
Is strangeness always, sometimes or never conserved?
sometimes
What property is never conserved?
mass
What property do particles such as kaons have?
strangeness
What are the values of strangeness?
+1, 0, -1
In which interaction is strangeness always conserved?
the strong interaction (when SNF acts between baryons and mesons
In which interaction is strangers not always conserved?
the weak interaction (when WNF acts)
What is the strangeness of a kaon plus?
+1
What is the strangeness of a kaon zero?
+1
What is the strangeness of an anti-kaon zero?
-1
What is the strangest of a kaon minus?
-1
How do we know an interaction is strong? What does this mean for strangeness?
- can’t involve leptons
- only involves hadrons
- strangeness is conserved
How do we know an interaction is weak? What does this mean for strangeness?
- will probably involve leptons
- usually 1 particle decaying into 2
- strangeness is probably not conserved
Via which interaction are strange particles created?
strong interaction
Via which interaction do strange particles decay?
weak interaction
By what amount(s) can strangeness change in the strong interaction?
0
By what amount(s) can strangeness change in the weak interaction?
+1, 0, -1
What special property do strange particles have?
strangeness
What is the role of an exchange particle in an interaction?
exchange particles transmit forces between particles by exchanging momentum and energy
What are exchange particles sometimes called?
gauge bosons
What is the exchange particle of the electromagnetic force?
virtual photon
Why is the virtual photon virtual?
because ‘seeing’ it would stop the force transmitting
What are the exchange particles of the weak nuclear force?
W+ and W- bosons
What is the exchange particle of the strong nuclear force?
pions - force between nucleons
& gluons - force between quarks
What is the exchange particle of gravity?
graviton (not yet observed)
What is the mass, charge and range of a virtual photon?
0 mass, 0 charge, infinite range
What is the mass, charge and range of W+ and W- bosons?
has mass, has charge, very short range
What is the mass, charge and range of pions (& gluons)?
has mass, has charge, very short range
What is the mass, charge and range of a graviton?
0 mass, 0 charge, infinite range
What diagram did Richard Feynman develop?
a simple and elegant system called Feynman diagrams
What are the rules for a Feynman diagram?
- before interaction at the bottom
- after interaction at the top
- baryons on the left
- leptons on the right
What is the relationship between the mass of an exchange particle and its range?
inversely proportional - the heavier the exchange particle, the shorter the range
What are the five Feynman diagrams you need to know?
- beta MINUS decay
- beta PLUS decay
- electromagnetic repulsion
- electron capture
- electron proton collision
What is the only difference between electron capture and electron proton collision?
the type and direction of the exchange particle
