Radioactivity Flashcards
Describe the plum pudding model of the atom
Positively charged sphere with negatively charged electrons embedded in it
Describe Rutherford’s model of an atom
Small, dense positively charged nucleus at the center surrounded by orbiting electrons
Describe Rutherford’s experiment
Alpha particles were fired at a thin gold foil and some particles were deflected or bounced back
What is the nucleon number (physics)
The total number of neutrons and protons
What is the proton number (physics)
The number of protons in an atom
Definition of isotope
Elements with different numbers of neutrons
What is a stable isotope?
Isotopes that don’t undergo radioactive decay
What is a radioactive isotope?
An isotope who’s nucleus is unstable and dcays to emit radiation
What is radioactive decay?
The spontaneous process where an unstable atomic nucleus loses energy by emitting radiation
What does “Radioactivity is a random process” mean?
It is impossible to predict when an individual nucleus will decay but you can make predictions on a much larger scale
What does “Radioactivity is a spontaneous process” mean?
You cannot control the process of radioactive decay
What are the 4 types of radioactive decay?
Alpha - α
Beta - β
Gamma - γ
Neutron - n
What is a daughter nucleus?
The nucleus that results from the radioactive decay of a parent nucleus
What is background radiation?
The naturally occuring radiation present in the environment
What are 4 sources of background radiation?
Radon gas
Cosmic rays
Rocks
Human activity (nuclear waste etc)
How does nuclear radiation cause ionisation?
Radiation knocks electrons out of atoms
Why is a more ionising particle less penetrating?
It loses energy faster as it travels so it doesn’t get as far
How can ionising radiation be detected (2 ways)
G-M detector
Photographic film
What kind of nucleus is an alpha particle
Helium nucleus
What is an alpha particle made up of
2 Neutrons
2 Protons
Rank the most penetrating radiation to least
- Gamma
- Beta
- Alpha
Rank the most ionising radiaton to least
- Alpha
- Beta
- Gamma
Why are alpha particles strongly ionising?
They are big, heavy and slow-moving
They collide with lots of atoms and knock lots of electrons out of them
What is the effect of electromagnetic fields on alpha particles?
Alpha particles have a positivecharge
They feel electromagnetic forces
What kind of particles are beta particles?
Fast moving electrons
How are beta particles emitted?
Emitted from nucleus when (high energy) neutron turns into a proton and electron
What is the size and speed of a beta particle?
Quite small
Quite fast
What is the size and speed of an alpha particle?
Large
Slow
What is the mass of a gamma ray?
No mass
What is the effect of electromagnetic fields on beta particles?
They are negatively charged
They feel electromagnetic forces
Why are gamma rays very penetrating
They are so small they tend to pass through atoms
What is the size and speed of a gamma ray?
No mass
Fast
When does gamma emission occur?
Always after beta or alpha decay
When a nucleus has excess energy
Never ALONE
What materials block alpha particles
paper
skin
a few cm of air
What materials block beta particles?
thin aluminium
What materials block gamma rays?
Thick lead
Very thick concrete
Why do we measure background radiation?
To work out how much radiation isn’t emitted by the source
What is an alpha particle in a nuclear equation?
⁴₂He
What is a beta particle in a nuclear equation?
⁰₋₁β
What is a gamma ray in a nuclear equation?
⁰₀γ
What is a neutron in a nuclear equation?
¹₀n
What is half-life
The time taken for half of a radioactive substance to decay or its activity to half
What is activity (physics)
The rate at which a radioactive source decays
How do you measure half-life with a graph?
Measure the time that it takes for activity to half
Repeat
Average
What kind of radiation do medical tracers use?
Why?
Beta and Gamma
Both will penetrate the skin
Both are not harmful in short exposure
What kind of half life should a medical tracer have?
Short (a few days)
So damage is not caused by over exposure
How is radiation used to treat cancer?
Radiotherapy kills cancer cells
What type of radiation is used in radiotherapy
Gamma
How can food and equipment be sterilised? (radioactivity)
Irradiated with gamma rays
How can radiation be used to detect leaks in pipes?
Gamma source flows down pipe
Detector above ground
It pools where leak is and higher count is detected
How is radiation used in thickness control?
Beta source points at paper
GM Counter
Thicker paper -> lower count
Thinner paper -> higher count
Rollers adjusted accordingly
Why does ionising radiation damage cells?
Radiation collides with molecules in cells
Can cause cell mutation or death
What is irradiation?
Objects exposed to radioactive radiation
What is contamination?
When radioactive particles are transferred to objects they should not be on
How can we prevent irradiation?
Lead-lined boxes
Protective clothing
Long tongs
etc
How can we prevent contamination?
Tongs
Gloves
Masks
etc
What is radioactive waste?
Items that are radioactive or contaminated by radioactive materials that have no further use
How can low-level radioactive waste be disposed of?
Burying in landfill
How can high-level radioactive waste be disposed of?
Sealed into glass blocks
Then sealed into metal canisters
Then buried deep underground
What is nuclear fission?
The splitting of an atom, which releases energy
Is nuclear fission spontaneous?
No - it can be controlled in a nuclear reactor
What isotope of uranium is used in a nuclear reactor?
Uranium-235
Describe the process of nuclear fission
- A slow-moving neutron is absorbed by uranium-235
- Nucleus splits into 2 daughter nuclei and 2/3 fast neutrons
- Energy is released
- Chain reaction
What is a fissile isotope?
A type of nucleus that can undergo nuclear fission when struck by a neutron
Why does nuclear fission produce radioactive waste?
The daughter nuclei of uranium-235 are usually radioactive
How does a nuclear reactor work?
Nuclear fission warms gas
Steam is produced
Turbine is driven
What material is the moderator in nuclear reactors?
Heavy water or graphite
What is the role of the moderator in nuclear reactors?
To slow down fast-moving neutrons so they can be absorbed by another uranium-235 atom
What is the material of fuel rods in nuclear reactors?
Uranium-235
What is the material of control rods in nuclear reactors?
Boron or Cadmium
What is the role of control rods in nuclear reactors?
They absorb some fast neutrons to control the rate of reaction
Can be raised/lowered
What radiation is released in fission?
Fast neutrons and gamma rays
What is the role of shielding around a nuclear reactor?
To absorb the ionising radiation produced in fission
What material is the shielding around a nuclear reactor made of?
Concrete
Don’t forget fusion is yet to be added to this deck
