Radiation Flashcards
What was the plum pudding model of an atom?
When Thomson, in 1897, discovered electrons could be removed from atoms, showing they have structure, he came up with the idea that matter was made up of positive spheres (atoms) with electrons stuck in them
What are the similarities of the plum pudding model to the modern day model of an atom?
- Have positive and negative charges
- Have electrons
- Spherical
What are the differences of the plum pudding model to the modern day model of an atom?
- No nucleus
- No neutrons
- Electrons in middle, not round outside
- No empty space
- Positively charged sphere, not nucleus
What was the Rutherford scattering experiment?
Alpha particles (2 protons and 2 neutrons) were fired at thin gold foil to try and prove or disprove the plum pudding model
What three things were discovered during the Rutherford scattering experiment?
- Most particles passed straight through, showing there is mainly empty space
- Very few particles were deflected straight back, showing the atom has a positive nucleus as the positive alpha particles were repelled
- This also showed that the concentrated mass in the nucleus is very small compared to the size of the atom, but contains most of the mass
What are two properties of radioactive substances?
- Radioactive substances give out radiation from the nuclei no matter what is done to them
- Radioactivity is entirely random, and unaffected by physical conditions such as temperature
What are isotopes?
Atoms with the same number of protons but a different number of neutrons
How many elements have isotopes?
Most elements have different isotopes, but there are usually only one or two stable ones
What happens to the isotopes which are less stable?
The others tend to decay into other elements and give out radiation
What are the three types of radiation?
Alpha (α), Beta (β), Gamma (γ)
What are alpha particles made from, what is their charge, mass and speed, what are they stopped by and how powerful are they at ionising and penetrating?
- Made from: two protons and two neutrons that have been kicked out of a nucleus
- Charge: +2
- Mass: 4
- Speed: slow
- Stopped by: a sheet of paper
- Ionising: strong, bash into atoms and knock off electrons
- Penetrating: low
What are beta particles made from, what is their charge, mass and speed, what are they stopped by and how powerful are they at ionising and penetrating?
- Made from: a fast moving electron
- Charge: -1
- Mass: 1/2000
- Speed: quite fast
- Stopped by: few mm of aluminium
- Ionising: moderate, bash into atoms and knock off electrons
- Penetrating: medium
What are gamma particles made from, what is their charge, mass and speed, what are they stopped by and how powerful are they at ionising and penetrating?
- Made from: very short electromagnetic waves
- Charge: 0
- Mass: 0
- Speed: speed of light
- Stopped by: few cm of lead
- Ionising: weak, tend to pass through rather than collide
- Penetrating: high
What is background radiation?
Radiation that is present at all times
What are some natural causes of background radiation?
-Cosmic rays
-Rocks and soil - give off radon
-Living things (plants absorb
radioactive materials from the soil and pass them up the food chain)
What are some artificial causes of background radiation?
- Waste from nuclear power stations
- Nuclear weapons testing
- Medical x-rays
What are some uses of radiation?
Smoke detector -Weak α radiation is put between 2 electrodes, causing ionisation and enabling a current to flow. In a fire, smoke absorbs the radiation, stopping current and sounding the alarm
Medical tracers -Certain isotopes are ingested and progress around the body is measured. All isotopes must be γ or β so radiation passes out of the body and have a short ½ life so radiation disappears
Radiotherapy -High doses of γ radiation is directed at cancer cells to kill them without damaging too many normal cells
Sterilisation of food and surgical equipment -High doses of γ rays kill all living cells, including microbes. The isotope has a long ½ life so doesn’t need to be replaced often
What is nuclear fission?
- Splitting up of a large atomic nucleus
- Energy released heats water, which turns into steam and drives a turbine, creating electricity
- A slow moving neutron is absorbed by uranium or plutonium nucleus, making it unstable and causing it to split. When it splits, 2 or 3 more neutrons are released to carry on the reaction
What are the pros and cons of nuclear fission?
Pros -Cheap fuel, give out lots of energy
Cons -Difficult waste disposal, high cost of power plant and decommissioning
What is nuclear fusion?
- Joining together of small atomic nuclei
- Energy in stars comes from fusion and lots of energy is released
What are the pros and cons of nuclear fusion?
Pros -Little radioactive waste, lots of fuel around
Cons -Only happens at very high temperatures (10,000,000°c), needs strong magnetic field to store it
