- Created by: abbiedye
- Created on: 29-07-18 11:04
What is an isotope?
- Atoms of an element with the same number of protons (same atomic number and charge of the nucleus) but a different number of neutrons (different mass number)
- All elements have different isotopes but only one or two are stable
- The others decay and give out radiation
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Current model of the atom
- Nucleus = tiny - most mass though, protons (positive, +1) and neutrons (neutral, 0) positive charge, 10,000 times smaller than the atom
- Electrons = relative charge (-1), give the atom the overall size, can move within or leave the atom, gain energy from EM radiation - higher energy levels
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How was the model of the atom developed?
- John Dalton - agreed with Democritus - atoms were tiny spheres - couldn't be broken
- JJ Thompson - plum pudding - positive 'dough' with a lot of negative electrons
- Rutherford - alpha particle scattering - deflected - concentrated mass in centre but mostly empty space
- Niels Bohr - a cloud of negative electrons - orbit in shells - nucleus = protons
- James Chadwick - neutron - nucleus
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What is alpha radiation?
- When an alpha particle is emitted from the nucleus. An alpha particle is two neutrons and two protons (helium nucleus)
- They don't penetrate very far and are stopped quickly. They can only travel a few cms in air and are absorbed by a sheet of paper
- Size - strongly ionising
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What is beta radiation?
- Fast moving electron released by the nucleus - no mass and a charge of -1
- Moderately ionising - penetrate moderately far into materials before colliding and have a range in air of a few metres - absorbed by a sheet of aluminium (5mm)
- For every beta particle emitted, a neutron in the nucleus has turned into a proton
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What is gamma radiation?
- Gamma rays are waves of electromagnetic radiation released by the nucleus
- Penetrate far into materials without being stooped and will travel a long distance through the air - weakly ionising, tend to pass through rather than collide with atoms - eventually they hit something and do damage
- They can be absorbed by thick sheets of lead or metres of concrete
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What are nuclear equations?
- A way of showing radioactive decay by using element symbols
- Written in the form - atom before decay -> atom after decay + radiation emitted
- Rule = total mass and atomic numbers must be equal on both sides
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What is alpha decay?
- Alpha particle - two protons and two neutrons - when an atom emits an alpha particle, its atomic number reduces by 2 and its mass number reduces by 4
- proton - positively charged + a neutron - neutral - charge decreases
Uranium-238 -> Thorium-234 + alpha particle
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What is beta decay?
- A neutron in the nucleus turns into a proton and releases a fast-moving electron
- Number of protons in the nucleus increases by 1 - increases positive charge of the nucleus (the atomic number)
- Nucleus has lost a neutron and gained a proton during beta decay - the mass of the nucleus doesn't change
Carbon-4 -> Nitrogen-14 + beta particle
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What is gamma decay?
- Gamma rays are a way of getting rid of excess energy from a nucleus - no change to the atomic mass or atomic number of the atom
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What is radioactivity?
- Radioactive substances give out radiation from their nuclei - no matter what
- Radiation can be measured with a Geiger-Muller tube and counter - records the count-rate
- Radioactive decay - entirely random
- The time it takes for the amount of radiation emitted - half-life (becquerels)
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What is half-life?
- The half-life is the time taken for the number of radioactive nuclei in an isotope to halve
- Some isotopes take a few hours before all unstable nuclei have decayed, whilst others last for millions of years
- Time taken for the activity to half its initial value
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Why are there risks to using radiation?
- Ionising radiation can enter living cells and ionise atoms within them
- They can damage cells (cancer) or kill them off completely
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What is irradiation?
- Objects near radioactive sources are irradiated by it (exposed to it)
- Irradiating something does not make it radioactive
- Reducing effects - keep sources in a lead-lined box, stand behind barriers, different room - remote-controlled arms
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What is contamination?
- If unwanted radioactive atoms get onto or into an object
- Contaminated atoms might then decay, releasing harmful radiation - dangerous - could get inside the body
- Gloves, tongs and protective suits help for sources not to get trapped in the skin, under nails or breathed in
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Seriousness of irradiation and contamination
- Cause different amounts of harm, based on radiation type
OUTSIDE THE BODY
- beta and gamma are most dangerous, they penetrate the skin
- alpha can't penetrate the skin, blocked by a small air gap
INSIDE THE BODY
- alpha is most dangerous, damage in localised area, contamination = concern
- beta, less damaging, absorbed and passes out of the body
- gamma, least dangerous, pass straight out
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