Studied by 16 people
What is an exchange particle?
A virtual particle that lets a force act between 2 particles in an interaction.
What is an application of annihilation?
PET scanners
How do PET scanners work?
A positron emitting isotope is injected into the blood stream
The scanner then detecets the gamma rays produced from the electron-positron annihilation that occurs.
The graph shows that the electrons have a range of kinetic energies. If the only 2 particles emitted were the electrons and neutrons, then the kinetic energies of the electrons would be the same. Therefore, there must be another particle carrying the “missing energy” away.
Why are scientific models only adopted over a period of time and not instantly?
Rigorous testing through experiments must be done before a model can be accepted. If the results cannot be repeated, then the model is wrong.
The model must also be peer reviewed to evaluate the research.
What is another term for exchange particles?
Gauge bosons.
What are A and Z in the atom?
A = Number of nucleons
Z = Number of Protons (And Electrons)
What element’s vapour is contained in a florescent tube?
Mercury vapour.
What property defines a hadron?
Particles that experience the strong nuclear force
Are strange particles more massive than u or d quarks?
Yes, resulting in the being heavier.
How can you tell whether it is a Strong or Weak interaction?
If leptons involved and/or strangeness not conserved = WEAK
If hadrons & strangeness conserved = STRONG
If the reactants combined rest energy is less than the products combined rest energy, what has occurred? (2 marks)
Kinetic energy of the reactants is greater than the kinetic energy of the products. This kinetic energy is then used in the rest energy of the products.
In terms of collisions, are both photons and electrons fully absorbed?
NO!
Photons ARE absorbed. They must lose all their energy or will not be absorbed at all.
Electrons are NEVER absorbed, and can lose any amount of its kinetic energy.
(there was a question on this!)
Why would a nucleus undergo electron capture?
Because it is proton rich. It wants to convert protons to neutrons.
What is the difference between electron capture and electron-proton collisions?
In electron capture, a proton within a nucleus captures an electron from the atom, turning into a neutron and also emitting a neutrino.
In electron-proton capture, a free electron is fired at a free proton and collides with it, producing a neutron and a neutrino.
What is the exchange particle for electron capture, and what particles are produced?
W+ boson.
Neutron and an electron neutrino.
How many quarks does a meson have?
2
How many quarks does a baryon have?
3
What special property do strange particles have?
They are always produced in pairs
In what type of interaction do strange particles decay?
Weak interaction
In what type of interaction is strangeness conserved?
Strong interaction only.
What properties are always conserved in particle interactions?
Charge (Q), Baryon Number (B), Lepton Number (Le and Lu), Energy, Mass & Momentum
What is specific charge?
The specific charge of a particle is the ratio of its charge to its mass, given in Ckg-1
Describe the role of B decay in the prediction of the existence of the neutrino.
It appeared that in B decay, energy was not being conserved. The neutrino was hypothesised as a particle that had no mass (as it hadn’t been detected before) and had no charge (to conserve charge) but allowed energy to be conserved.
A proton and an antiproton are produced by a proton-proton collision. Name this process.
Pair production
An antiproton and a proton interact. Name the process and state what is produced.
Annihilation, two gamma ray photons
What is the quark combination of K+?
up, anti-strange
What is the quark combination of K-?
strange, anti-up
What is the quark combination of K0?
EITHER:
down, anti-strange
strange, anti-down
What is the quark combination of π+?
up, anti-down
What is the quark combination of π-?
down, anti-up
What is the quark combination of π0?
EITHER:
up, anti-up
down, anti-down
strange, anti-strange
What interaction creates strange particles?
Strong interaction
What interaction must strangeness be conserved?
Strong interaction
How much can strangeness change by during the weak interaction?
0,-1 or +1
State what roles exchange particles can play in an interaction
Transfers: energy, momentum, force and sometimes charge
An electron collides with a neutral atom and ionizes it. What are the particles present after the collision?
2 electrons and a positive ion
Artificial radioactive nuclides are manufactured by placing naturally-occurring nuclides in a nuclear reactor. They are made radioactive in the reactor as a consequence of bombardment by what particle?
Neutrons.
What is the specific charge of an electron?
-1.60×10-19C
What term means 'per unit mass' when describing a physical quantity?
Specific
What are the letters form both Nucleon Number and Proton Number?
Nucleon number: A
Proton number: Z
What is the approximate radius of a nucleus relative to the atom?
1×10-5
How are the electrons in an atom organised?
In orbitals (shells)
Which subatomic particle has a relative atomic mass of 1/2,000?
Electrons
What are the units of specific charge?
C/kg
What is a nuclide?
A nuclide refers to a specific nucleus that contains a certain number of protons and neutrons. (A nuclide is a specific isotope of an element)
Explain how radioactive carbon-14 can be used to find the age of a fossil. (3 marks)
All living organisms have the same amount of carbon-14 atoms as a percentage of all carbon isotopes.
Once the organism dies, it no longer absorbs carbon from the atmosphere.
Carbon-14 is radioactive and so will decay over a known half life.
(The older the fossil is, the fewer carbon-14 isotopes it will contain and the less radiation it emits.)
What property of fossils are determined by using carbon isotopes?
Age
The distance at which the strong nuclear force becomes repulsive is about what?
0.5fm and under
When does alpha decay occur?
In very large nuclei (containing more than 82 protons)
When does Beta minus decay occur?
When a nuclei has too many neutrons.
Why was the Antineutrino hypothesised? (5 marks)
When scientists first observed beta decay, they thought that neutrons were decaying into a proton and an electron only.
They noticed that the energy of the neutron before the decay was larger than the energy of the proton and electron after the decay: energy was not being conserved.
To account for this, scientists hypothesised that a new type of particle was being produced and carrying away some energy.
This particle must have zero (or almost zero) mass and must be electrically neutral (to obey charge conservation).
This particle was then called a neutrino but we now know it to be an antiparticle called an antineutrino.
Which subatomic particle is not affected by the strong nuclear force?
Electrons
What would happen to a nucleus without the strong nuclear force?
Break apart
What is meant by the AZX notation for atoms?
The AZX notation is used in decay equations to represent different isotopes of an element X
A represents the nucleon number
Z represents the proton (atomic) number
What is Molecule labelling?
Molecule labelling uses radioactive isotopes to track mechanisms of specific molecules.
A regular atom is swapped out for an isotope, which behaves exactly the same due to the proton number being the same.
The isotope is detectable due to its differing number of neutrons.
Why might carbon dating not be so reliable in the future?
Carbon isotope ratio is being altered by humans.
What are the products of Annihilation? (2 marks)
A pair of gamma photons
The energy carried aa must equal the total energy of the particles to begin with (kinetic energy + rest mass energy)
(Each gamma photon must carry away at least the rest mass energy of one particle)
What are the products of Pair production? (2 marks)
Particle-Antiparticle pair
Energy of the photon with spontaneously turns into the pair must have at least the total rest mass energy of the pair it creates.
What is the weak nuclear force responsible for? (3 marks)
The weak nuclear force is responsible for beta-plus and beta-minus decay, as well as electron capture interactions.
Which fundamental force is responsible for contact forces?
Electromagnetic force
What is the exchange particle for the strong nuclear force?
Gluon/pion
What is the exchange particle for the electromagnetic force?
Virtual photon (called “virtual” as they only exist for a very short time)
What are the 3 exchange particles for the weak nuclear force?
W+
W-
Z0
What are exchange particles sometimes also called?
Gauge bosons
What are the two types of Hadrons?
Baryons - containing 3 quarks. (Protons, neutrons)
Mesons - containing 2 quarks (Pions, kaons)
Where can Mesons be found? (2 marks)
Cosmic rays
Particle accelerators
What are Leptons made up of?
Nothing, they are fundamental particles (Electrons, Muons, Neutrinos)
Do Leptons feel the SNF?
NO!
What are Muons? (2 marks)
Heavier than electrons
Unstable and always decay into electrons
Where are Muons found? (1 mark)
Cosmic Rays.
What are Neutrinos? (2 marks)
Leptons that are massless with 0 charge
What are the 2 types of Lepton numbers?
Electron lepton number (Le)
Mon lepton number (Lu)
What is the only interaction where strangeness is conserved?
Strong interaction (SNF)
What interaction are strange particles produced and what interaction decays them?
Strong interaction produces strange particles (Kaons are always produced in pairs)
Weak interaction decays strange particles (Strangeness can change by -1,0 or +1 only)
What type of number are lepton and baryon numbers? (1 mark)
Quantum numbers
Which photons have the most energy? (1 mark)
Gamma
What kind of photon is produced in annihilation? (1 mark)
Gamma
Can exchange particles both push particles together & pull particles apart?
Yes.
What is the antiparticle for π0
π0
(itself)
What mesons contain strange quarks?
ONLY Kaons.
How can quarks change type?
Through the weak nuclear force
How many quarks can change at one time in a weak interaction?
1 quark
Why do scientists need to work collaboratively in particle physics? (3 marks)
Particle physics experiments create massive amounts of data.
Particle physics experiments are also very expensive to run.
Large teams working collaboratively are needed to validate new knowledge in particle physics.
Why is an anti-electron neutrino produced in beta-minus decay?
In order for Lepton number to be conserved.
e- = Le = 1
Anti electron neutrino = Le -1
As we had no leptons at the start, now lepton number is balanced
Why is a neutrino produced in beta-plus decay?
In order to conserver Lepton number.
A positron is produced (Lepton number -1)
An electron neutrino is also produced (Lepton number +1)
Therefore Lepton number is conserved.
What particle is NOT affected by the weak interaction? (1 mark)
Photon
Is the electron neutrino a fundamental particle?
Yes.
Is the energy of a photon directly proportional to the frequency of the radiation?
Yes
What photons have the highest frequency?
Gamma photon
Which photons have the lowest frequency?
Radio photons
Why are Kaons always produced in pairs?
Kaons are produced via the strong interaction
Strangeness is conserved in the strong interaction
Therefore, kaons must be produced in pairs to cancel out the strangeness value (-1 +1 =0)
Can forces act instantaneously?
No
What is the exchange particle of the strong nuclear force between quarks?
Pion/Gluon
What is the only interaction that can change quarks “flavour”?
Weak interaction
What are the two types of lepton numbers that need to be conserved separately?
Lepton electron number
Lepton muon number
What is the electron lepton number of a muon antineutrino?
0
What is the difference between strong force and weak force?
Strong force occurs when hadrons interact
Weak force occurs when a quark changes, and there is a decay
What is the photon theory of light?
One photon emits one electron if the photon is above the threshold frequency.
What property defines a hadron?
Experiences the strong nuclear force
Note 
Flashcard (108)