Nuclear Flashcards
Alpha scattering conditions
Same speed alpha particles (or slower will be deflected more)
Vacuum or the alpha particles will be stopped
Long half life ( so later results not lower due to decay)
Lead shield to direct particles and give a columnated beam
Thin gold foil so only scattered once
Alpha
2 protons, 2 neutrons Range in air ≈ 100mm Very ionising 10^4 ions per mm in air Stopped by paper Deflected in magnetic and electric fields
Beta
Range in air ≈ 1 m
Stopped by ≈ 5mm aluminium
≈100 ions per mm in air
Deflected by magnetic and electric fields (more easily than alpha)
Gamma
Height frequency em radiation Intensity = k/d ^2 - inverse square law Not deflected in magnetic and electric fields Mildly ionising Very penetrating Stopped by several cm of lead
Sources of background radiation
Air, medical, ground and buildings, food and drink, cosmic rays, nuclear power, nuclear weapons, air travel
Randomness of decay
Cannot predict which nucleus in a sample will decay
Cannot predict when a nucleus in a sample will decay
Energy released per second
AE
Decay equations
N = No e^(- lambda t) A = Ao e^(- lambda t) A = lambda N
Half life equation
T1/2 = ln2/ lambda
Uses of isotopes
Carbon dating Argon dating Radioactive tracers Engine wear Thickness monitoring Power sources for remote devices
Why electrons are suitable for radius estimation
Can be accelerated
Have a de Broglie wavelength of ≈ 10^-15 which is similar to the diameter of the nucleus
Nuclear radius and atomic mass equation
R = ro A^1/3
ro = 1.05 fm
Energy and mass
E = mc^2
Energy transfer in beta decay
Energy released shared between beta particle, neutrino and nucleus
Beta particle has max Ek when neutrino has minimum
Max Ek beta particle is less than energy released due to conservation of momentum and the recoil velocity of the nucleus
Mass defect and binding energy
dm = mp + mn - m nuc
BE = dm c^2
Nuclear stability
Greater binding energy per nucleus = more stable
Most stable A= 50 to A=60
Why nuclei need to collide at high speeds for fusion
To overcome the electrostatic repulsion between the 2 nuclei
Come close enough to interact via the strong nuclear force
Advantages of fusion power
Releases more energy than fission per unit mass of fuel
Abundant fuel (deuterium in water)
Safer products of reaction ( less radioactive)
Fuel rods
Enriched uranium
U-238 and 2-3% fissionable U-235
Control rods
Usually boron ( has stable isotopes)
Absorb neutrons to control reaction
Keep number of neutrons in core constant
≈ 1 fission neutron per fission event goes on to induce further fission
Moderator
Water or graphite (will slow the neutrons but not absorb them)
Fission neutrons need to be slowed down so that they can go on to induce further fission
Slows neutrons down via multiple collisions with the moderator molecules
Cooling system
Needs to be under pressure
Prevent water evaporating (greater specific heat capacity as a liquid) or to increase the thermal capacity of CO2
Safety features
Reactor core is a thick steel vessel (to withstand heat and pressure) that will absorb alpha and beta and reduce gamma and neutrons
Building has thick concrete walls to absorb gamma and neutrons
Reactor has emergency shut down system- will insert control rods fully
Fuel rods inserted and removed via remote handling
High level waste
Spent fuel rods
Contain many radioactive isotopes (fission products, unused U-235)
Disposal of high level waste
Removed by remote control Cooled in water for many months Vitrification (sealed in glass) Put in a steel capsule and steel flask Transported carefully Stores for a long time
Intermediate level waste and disposal
Parts of the power station, radioactive materials with low activity, containers of radioactive materials
Sealed in drums encased in concrete
Stored in buildings with walls of reinforced concrete
Low level waste and disposal
Lab equipment, protective clothing
Sealed in metal drums and buried in large trenches
