Nuclear and Particle Physics Flashcards
What is nucleon number?
The sum of the number of protons and neutrons in the nucleus
What is atomic number?
The total number of protons in the nucleus
Outline Rutherford’s alpha scattering experiment
- High speed alpha particles were fired at a very thin sheet of gold foil.
- The deflections of the particles were measured and conclusions were drawn
What was observed in the Alpha Scattering Experiment?
- Most of the alpha particles passed straight through the gold atoms
- Some of them were deflected
- A few of them were deflected backwards
What is thermionic emission?
Thermionic emission is the release of electrons due to heating
Explain why electrons are released from a heated filament?
- As the filament heats up, free electrons inside the metal gain kinetic energy.
- When the surface electrons gain sufficient energy, they are released from the surface
What will happen to a beam of electrons it is passed through a potential difference?
The beam of electrons will be accelerated since work is done by the potential difference
How do you calculate the energy transferred to an electron, when it is accelerated across a potential difference?
Energy = Charge X Potential difference
Energy = eV
What happens when a beam of electrons is directed into a magnetic field?
The electron beam will be deflected since magnetic fields apply forces on moving charges
What is the magnitude of the force experienced by a moving electron in a magnetic field?
Force = Magnetic Flux Density x Charge x velocity
F = Bev
if the electrons are moving perpendicular to the field lines, which direction will the magnetic force act?
The force will act perpendicular to both the electron and field directions
Describe the shape of the path of a beam electrons passing through a magnetic field
- The beam will produce a circular path since the magnetic force always acts perpendicular to the electrons’ motion.
- This means it acts as a centripetal force and produces a circular path
What is a cyclotron?
A cyclotron is a particle accelerator that uses magnetic fields to accelerate particles in circular paths.
This allows higher speeds to be reached, without the limitation of the accelerator’s length
Describe the basic composition of a cyclotron
Cyclotrons consist of two D-shaped paths which are separated by a small gap.
An alternating potential difference is applied across the gap
How does a cyclotron work?
- An electron beam is passed into the cyclotron
- it is deflected into a circular path by a perpendicular magnetic field
- When the beam reaches the gap, it is accelerated by a potential difference.
- This increases the speed of the beam, causing the radius of the path to increase
- This process repeats every half circle
State the equation used to calculate the circular path of an electron beam deflected in a magnetic field
Radius = mv/ BQ
What two equations must you combine to derive the radius equation?
- Centripetal force = mv^{2} / r
- Magnetic Force = BQv
Centripetal force = Magnetic force
State the mass-energy equation
E = mc^{2}
What is 1 MeV in joules?
(1.6 x10^{-19}) x 10^{6} = 1.6 x 10^{-13}
In the quark-lepton model, what are the four main categories of particles?
- Baryons
- Mesons
- Leptons
4.Photons
Describe the quark composition of a baryon
Baryons are made up of three quarks
Describe the quark composition of a meson
Mesons are made up of a quark and antiquark pair
Which category of particles are classed as fundamental particles?
Leptons
Give two examples of leptons
- Electrons
- Neutrinos
What category of particles do pions belong in?
Mesons
Give two examples of baryons
- Protons
- Neutrons
What did the symmetry of the quark-lepton model predict the existence of?
The top quark
What is an antiparticle?
An antiparticle is one that has the same mass but opposite charge and conservation charge numbers to its corresponding particle
What is the antiparticle of a proton?
An antiproton
What is the antiparticle of an electron?
A positron
Name four things that are always conserved in a particle interaction
- Mass/ Energy
- Baryon number
- Lepton number
- Charge
Describe the conservation of lepton number.
The Lepton number for each specific type of lepton must be the same before and after an interaction
What two processes can cause electrons to change energy levels?
Excitation and Ionization
What are the four scenarios in which an atom may become unstable?
- The atom having too many neutrons
- The atom having too few neutrons
- The atom having too much mass
- The atom having too much energy
How do unstable nuclei become more stable?
Unstable nuclei are radioactive so emit radiation in order to become more stable
The type of radiation they emit depends of what makes them unstable
What are the constituents of an alpha particles?
Two protons and two neutrons
What are penetration capabilities of alpha radiation?
Alpha particles are weakly penetrating and so are stopped by a few centimeters of air or sheet of paper
What does beta-minus radiation consist of ?
High-energy electrons
What does beta-plus radiation consist of?
High-energy positrons
What are the penetration capabilities of beta- minus radiation?
Beta-minus radiation has medium penetrative capabilities and is stopped by a few mm of aluminum or around 1 m of air
What are the penetration capabilities of beta-plus radiation?
Beta-plus radiation is almost instantaneously annihilated by electrons and so has virtually zero range
What is gamma radiation?
Gamma radiation is a form of high-energy electromagnetic radiation
What charge do gamma rays have
Gamma rays are a form of electromagnetic radiation and so don’t have a charge
Which type of radiation is most ionizing?
Alpha radiation
Which type of radiation is most weakly ionizing?
Gamma radiation
Which type of radiation travels the fastest and at what speed?
Gamma radiation travels the fastest since it is a type of electromagnetic radiation and so travels at the speed of light
Under what circumstance is alpha radiation emitted?
When nucleus has too much mass?
Under what circumstance is beta-minus radiation emitted?
Beta-minus radiation is emitted when a nucleus has too many neutrons
Under what circumstance is beta-plus radiation emitted?
Beta- plus radiation is emitted when a nucleus has too many protons
Under what circumstances is gamma radiation emitted?
Gamma radiation is emitted when a nucleus has too much energy
What are the penetrative capabilities of gamma radiation?
Gamma radiation is highly penetrative but is absorbed by several inches of lead or several meters of concrete
Explain the process of beta-minus decay
Beta-minus decay is where a neutron in the nucleus turns into a proton, and releases an electron and an electron antineutrino
Explain the process of beta-plus decay
Beta-plus decay is where a proton in the nucleus turns into a neutron, and releases a positron and an electron neutrino
How does the mass of a nucleus compare to the sum of the individual masses of its constituents?
The mass of the nucleus is always less the sum of the individual masses of its constituents
What is the name given to the difference in the mass of a nucleus and its individual constituents?
The mass defect
Explain why there is a mass defect in nuclei
The mass defect is a result of some of the mass being converted into energy used to hold the nucleus together
What is the name for the value of the energy required to hold a nucleus together?
binding energy
How can mass defect be used to calculate the binding energy of a nucleus?
By substituting the mass defect into Einstein’s mass energy equation
Why isn’t it useful to compare binding energies for different nuclei?
Different nuclei have different numbers of nucleons
What is a more useful measure used to compare the binding energies of different nuclei?
The binding energy per nucleon
State the equation used to calculate the binding energy per nucleon of a nucleus
Binding Energy per Nucleon = Binding energy/ The number of nucleons
What is the relationship between the stability of a nucleus and its binding energy per nucleon?
The large the binding energy per nucleon, the more stable the nucleus will be
What is the most stable nucleus?
iron
Name two nuclear processes that can be used to generate energy
- Nuclear fission
- Nuclear fusion
What are the two types of fission?
- Spontaneous fission
- Induced fission
Explain the basic process of induced fission
- A large nucleus absorbs a thermal neutron
- This causes it to split into two smaller nuclei
- This releases energy and at least one neutron
Explain the basic process of fusion
Two smaller nuclei join together to form a larger one, and releases energy in the process
Why is nuclear fusion not currently a feasible method of energy production?
- Nuclear fusion requires very high temperatures in order to overcome the electrostatic force between the nuclei
- This makes it hard to contain and means more energy must be inputted to heat the nuclei than is generated
Where does nuclear fusion constantly take place?
In stars ( the sun)
