Particles Flashcards
Give the relative mass of a proton, neutron and electron.
Proton = 1
Neutron = 1
Electron = 1/2000 OR negligible
Give the relative charge of a proton, neutron and electron.
Proton = +1
Neutron = 0
Electron = -1
Give the overall charge of an atom.
Neutral/Zero
Give the overall charge of a nucleus.
Positive
Give the approximate size of an atom.
1 X 10^-10 metres
Give the approximate size of a nucleus
1 x 10^-15
What is found between the nucleus and electrons?
Empty Space
In A-Z nuclide notation, what do A (one on top) and Z (one on bottom) represent?
A = Nucleon number
Z = Proton number/atomic number
In A-z nuclide notation, what defines which element it is?
Z, proton number as it changes the electronic configuration of the element
Give the definition of a nucleon number
Total number of protons and neutrons
Complete: Atoms have an equal number of … and …
Protons and electrons
How do atoms become positive ions?
By losing electrons
How do atoms become negative ions?
By gaining electrons
What is the magnitude of charge of an electron/proton?
1.6 x 10^-19 C
What is the mass of a nucleon?
1.67 x 10^-27 kg
What is the mass of an electron?
9.11 x 10 ^-31 kg
How do we work out the mass of an atom, ion or nucleus in kg?
Number of nucleons X 1.67 X 10^-27 (dont need to include electrons)
How do we work out the charge of a nucleus in coulombs?
Number of protons x 1.6 x 10^-19
How do we work out the charge of an ion in coulombs?
Relative charge x 1.6 x 10^-19
How do we calculate specific charge?
Charge/Mass
What are the units for specific charge?
Ckg^-1
What are isotopes?
Atoms with the same number of protons but a different number of neutrons
True or false: isotopes have different chemical properties.
False
True or false: isotopes have different nuclear stability
True
Describe the role of the strong nuclear force in nuclear stability
- Balances the electrostatic repulsion between positively charged protons.
- Holds nucleons in an equilibrium position (stops them moving further apart or closer together).
Is the strong nuclear force associated with charge?
No - acts equally between protons and neutrons
Describe how and explain why the strength of the nuclear force varies with nuclear separation.
Below 0.5 fm -> repulsive –> stops nucleons collapsing into a point.
Between 0.5 – 3.0 fm -> attractive –> binds nucleons.
Beyond 3.0 fm -> zero -> prevents nucleons in different atoms being attracted.
What type of nuclei normally undergo alpha decay?
Massive nuclei
What is an alpha particle made up of?
2 protons and 2 neutrons (a helium nucleus)
What is the general alpha decay equation in A-Z notation?
(A)(Z) X —-> (A - 4)(Z - 2) Y + (4)(2)a
What type of nuclei normally undergo beta minus decay?
Neutron rich nuclei
What is a beta minus particle?
An electron
Describe the change in the nucleons during beta minus decay
A neutron changes into a proton to achieve a more stable neutron to proton ratio
Name the extra particle emitted in beta minus decay
Electron anti-neutrino
Why the scientists hypothesise an additional particle in beta minus decay?
- Total energy after the decay was less than the total energy before.
- Missing energy must be carried away by another particle to conserve energy.
Why was it difficult to detect the additional particle in beta minus decay?
It has no mass and no charge
Write the general beta minus decay equation
(A)(Z) X —-> (A)(Z + 1) Y + (0)(-1) e- + Ve- (electron anti neutrino)
What type of nuclei normally undergo gamma decay?
Nuclei that need to lose excess energy
What is a gamma ray?
High energy EM wave
Which decay leads to the formation of an atom of a different element and why?
- Alpha and beta minus decay
- As the proton number changes
Describe the duality of EM radiation
Can act as a wave or a particle
What is a photon?
A quantum of EM energy with no mass or charge
What are the two equations for photon energy?
E = hf = hc/lambda
What units are the equations for photon energy calculating energy in?
Joules
What is the constant ‘h’ and what is it’s value?
- Planck’s constant
- 6.63 x 10^-34
What is the constant ‘c’ and what is it’s value?
- Speed of light
- 3 x 10^8
What is the energy of a photon directly proportional to?
- Frequency
- As E = hf
The energy of a photon is inversely proportional to?
- Wavelength
- As E = hc/lambda
Give the definition for the electron volt
The energy gained by an electron that is travelling through a potential difference of 1 volt
How do you convert from eV to J?
multiply by 1.6 x 10^-19
How do you convert J to eV?
Divide by 1.6 x 10^-19
How do you convert from MeV to J?
Multiply by 1.6 x 10^-19
What is one similarity between particles and anti particles?
- Mass
- Rest Energy
What is one difference between particles and anti particles?
Charge
What is the energy-mass equivalence?
- Energy can be converted into mass.
- Mass can be converted into energy.
- Calculated by E= mc^2
What happens in pair production?
A gamma photon interacts with a nucleus and the energy of the photon is used to create a particle and anti-particle pair.
In pair production, which pair of particles is most likely to be created?
Electron and positron as they have the lowest rest energy
Why does it need to be a gamma photon for pair production to occur?
Highest energy EM wave
How can we calculate the minimum energy of the photon required for pair production?
E(min) = 2 x rest energy of particle/anti particle
What happens in annihilation?
A particle meets its equivalent antiparticle.
Their mass is converted into energy in the form of two gamma photons.
Why are two gamma photons produced in annihilation?
They travel in opposite directions to conserve momentum
How can we calculate the minimum energy of one of the photons produced in annihilation and why is this the minimum energy of the photon?
- E(min) = rest energy of particle
- The particle and anti-particle may have additional kinetic energy
Describe the role of exchange particles in strong interactions
- Move between particles
- Give rise to the force between them
Name the four fundamental forces from strongest to weakest?
- Strong nuclear force (or strong interaction)
- Electromagnetic force
- Weak nuclear force (or weak interaction)
- Gravity
Which of the four dunamental forces do particle physicists normally ignore and why?
- Gravity
- So weak that it has a negligible effect
Give the exchange particle for the strong nuclear force
Pions
Give the exchange particle for the electromagnetic force
Virtual photons
Give the exchange particle for the weak nuclear force
W+ (when a particle gains electric charge) and W- (when a particle loses electric charge) bosons
Give the particles affected by the strong nuclear force
Hadrons
Give the particles affected by the electromagnetic force
charged particles
Give the particles affected by the weak nuclear force
All particles
Give the range of the strong nuclear force
1 x 10^-15
give the range of the electromagnetic force
infinite
give the range of the weak nuclear force
1 x 10^-18
Describe and explain the relationship between the mass of the exchange particle and the range of the force.
Larger mass -> shorter range.
Requires more energy to create -> only exists for shorter time -> shorter distance.
Draw a Feynmann diagram for the electromagnetic repulsion between two electrons.
e- on both top and bottom left and right mediated by a virtual photon
Draw a Feynmann diagram for beta minus decay.
n on the bottom left, proton on the top left, electron anti neutrino on the bottom right, e- on the top right, mediated by the W- boson going right
Draw a Feynmann diagram for beta plus decay
p on the bottom left, n on the top left, electron neutrino on the bottom right, e+ on the top right, mediated by the W+ boson going right
Draw a Feynmann diagram for electron capture.
p on the bottom left, n on the top left, mediated by the W+ boson going right, e- on the bottom right, electron neutrino on the top right
Draw a Feynmann diagram for electron-proton collision.
p on the bottom left, n on the top left, mediated by the w- boson going left, e- on the bottom right and electron neutrino on the top right
Draw a family tree for particle classification
Hadrons —> split into Baryons and Mesons
Leptons
Describe two differences between hadrons and leptons
- Hadrons experience the strong interaction but leptons do not.
- Hadrons are made up of quarks but leptons are fundamental.
Give two examples of baryons
- Protons
- Neutrons
Give the quark structure of baryons
3 quarks or anti quarks
Name the only stable baryon
Proton
Give the order of mass of quarks from greatest to smallest
- Greatest mass: strange quarks
- down quark
- Lowest Mass: up quark
Give two examples of mesons
Pions and kaons
Give the quark structure of mesons
A quark and antiquark
Are all mesons unstable?
Yes
What is the most stable meson and why?
Pions, lightest and therefore lowest energy
Name the strange meson, what does it’s strangeness tell you about it’s quark structure
Kaons -> contain a strange or anti-strange quark
How are kaons produced?
By the strong interaction -> produced in pairs of strange particles
How do kaons decay?
By the weak interaction -> decay into pions
Does the neutral pion and anti neutral pion have the same quark configuration?
No, can be up anti-up or down anti-down
Give the strangeness of the four kaons
K+ = +1
K- = -1
K0 = +1
anti K0 = -1
Does the neutral kaon and anti neutral kaon have the same quark configuration?
No, neutral is down anti-strange while anti neutral is strange and anti-down
Give three examples of leptons
Electrons, muons and neutrinos
Compare electrons and muons
- Same charge.
- Muons are heavier than electrons.
- Electrons are stable, but muons decay into electrons.
Give the mass and charge of neutrinos
Zero mass and zero charge
Describe the four particle interactions interaction conservation laws
- Baryon number: always conserved
- Charge: always conserved
- Lepton electron and lepton muon always conserved
- Strange: alwas conserved in strong interaction, in weak interaction can change by +1, -1 or 0
What six quantities need to be conserved in all interactions?
- Baryon number
- Charge
- Lepton electron and lepton muon number
- Strangeness (if mediated by the strong interaction)
- Energy
- Momentum
Why are strange particles produced in pairs?
Strangeness must be conserved as they are produced via the strong interaction, pair have equal and opposite strangeness so cancel to zero
In what type of interaction can quark character change?
Weak interaction only
What is the change in quark in beta minus decay?
down -> up
What is the change in quark in beta plus decay?
up -> down
What is quark confinement?
- Not possible for quarks to exist in isolation.
- The energy supplied to try separate a quark would cause pair production of another quark and anti-quark pair.
Why does particle physics research rely on the collaborative efforts of large teams of scientists and engineers?
- Particle accelerators are very expensive -> collaboration helps to spread the cost.
- Many skills and disciplines required.
- Lots of data to process.
- Results of experiments must be independently peer reviewed before confirmed.
What are the products when a free neutron decays?
proton + electron + electron anti-neutrino
Give the quark combination for a proton
uud
Give the quark combination for a neutron
udd
