Happens in a heavy nucleus. The proton number of the nucleus decreases by 2 and the mass by 4. A alpha particle and neutrino are emitted. Highly ionising, low penetrability. Quality factor of 20. Charge +2. Absorbed by paper or a few cm of air
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Explain beta radiation and decay?
Happens in a neutron rich nucleus. The proton number increases by 1. A electron and antineutrino are emitted and 1 neutron is changed proton . Medium ionising, medium penetrability. Quality factor of 1. Charge -1. Absorbed by 3mm of aluminium
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Explain gamma radiation and decay?
Happens in nuclei with too much energy. Very weakly ionising, high penetrability. Quality factor of 1. Absorbed by many cm of lead or m of concrete
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How does the intensity of gamma radiation change with distance?
It spreads out so intensity decreases. It decreases exponentially through concrete
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What is beta plus radiation?
A positron. It has virtually zero ionising and penetrating power as it is annihilated by an electron so doesnt get very far.
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What makes a nucleus unstable?
Too any neutrons, two few neutrons, too many nucleons (too heavy), too much energy
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What is the absorbed dose?
The energy absorbed per kilogram. Absorbed dose (Gy) = energy/mass
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What is the effective dose and what is it used for?
Effective dose (sv) = absorbed dose x quality factor and it lets you compare the amount of damage to bodily tissue
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Why is the quality factor for alpha radiation the highest (i.e it does the most damage)?
The particles are strongly positive so easily pull away electrons of atoms, ionising them. Every ionsation transfers energy from the alpha particle to the nucleus. The alpha particle can ionise about 10000 atoms before losing all its energy
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Why does beta cause less damage than alpha?
It has a lower mass and charge but a higher speed meaning it can still knock of electrons. Each particle ionises about 100 atoms so causes less damage
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What is the equation for risk?
Risk = Probability x consequence
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Why would a nucleus become unstable?
The balance of electromagnetic force pushing protons apart and strong nuclear force holding the nucleus together is not right
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What conservation laws must be considered in nuclear equations?
energy, momentum, proton number/charge, nucleon number, lepton number, baryon number
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Why does mass not need to be conserved?
E = mc^2 so energy released can account for any missing mass. Mass defect = mass of nucleons - actual mass
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What is equivalent to the mass defect?
The bbinding energy (The mass needed to separate all the nucleons in the nucleus)
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Explain the 'nuclear valley'?
This is a graph of b.e.p.n against nucleon number. B.e.p.n is at maximum around N=50. Most stable nuclei occur at minimum point (they are bound most strongly). The more -ve the b.e.p.n, the more energy required to remove nucleons from nucleus
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What is fission and why does it happen?
It happens to larger nuclei. It is spontaneous. It releases energy since smaller nuclei have larger binding energy per nucleon
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How does fission limit the number of possible elements?
The larger the nucleus, the more likely fission and hence really large nuclei would decay instantly.
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Explain fission?
When hit by neutrons, rods of uranium fission/split to form smaller nuclei and neutrons which cause more reactions.
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What is a moderator?
Something like water to slow down or absorb neutrons
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What are control rods?
Boron rods absorb neutrons so the rate of fission is controlled
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What is a coolant?
Something like water used to remove heat
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What is sub-critical mass?
Too many neutrons absorbed so reaction dies out
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What is critical mass?
One fission follows another
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What is super-critical mass?
Several fission follower another (used in reactors)
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What are the problems with waste products of fission?
They are radioactive and very hot so can be stored underground and put in cooling ponds
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What is fusion?
Where light nuclei join together if they have enough energy to overcome the electrostatic repulsion between them and get close enough
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Why does fusion happen in stars?
Temperatures are very high so atoms not exist, you have plasmas where the electrons are stripped away. A lot of energy is released since heavier nuclei have a larger binding energy per nucleon. This helps to maintain the stars temperatue
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Does fusion or fission release the most energy?
Fission
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What are the equations relating to shielding?
Intensity = inital intensity.e^-mu.x where x is thickness and thickness when intensity has halved = ln2/mu
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Other cards in this set
Card 2
Front
Explain beta radiation and decay?
Back
Happens in a neutron rich nucleus. The proton number increases by 1. A electron and antineutrino are emitted and 1 neutron is changed proton . Medium ionising, medium penetrability. Quality factor of 1. Charge -1. Absorbed by 3mm of aluminium
Card 3
Front
Explain gamma radiation and decay?
Back
Card 4
Front
How does the intensity of gamma radiation change with distance?
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