P6.2 Flashcards
Give examples of background radiation:
- radon gas
- artificial sources - medical uses
- ground and building
- food and drink
- cosmic rays
How does ionising radiation harm living cells and how does it differ with different amounts of radiation?
- some materials = absorb ionising radiation = enters living cells and interacts with molecules
- molecules ionise to produce charge particles (ions)
- lower doses of ionising radiation = damage living cells by causing mutations in the DNA = cells did ice uncontrollably = cancer
- higher doses = kill cells completely = radiation sickness
What effects which radiation is the most dangerous?
Depends on where it is
What radiation is the most dangerous outside the body and why?
- beta, gamma
- as they can still get inside to the delicate organs as they can pass through skin
What radiation is the most dangerous inside the body
- alpha source
- most ionising as they do all their damage in a very localised area
- beta and gamma are less dangerous as less ionising and gamma will pass straight out without doing much damage
What does irradiation occur?
- occurs when radioactive material is outside your body but the radiation can travel to your body
What is the risk or irradiation and what does it depend on?
- risk of irradiation form a source is how likely that an object will be irradiated by source
- depends on distance from source and type of radiation source emits
- distance from source increases= amount of radiation reaching point decreases = irradiation risk lower
Why is the irradiation risk lower for sources that emit alpha radiation ?
- alpha = shorter range compared to gamma
- irradiation risk = lower for source emitting alpha at given distance
When does contamination occur?
- radioactive material is taken on the skin or inside the body
- internal contamination = can’t be removed
What is the contamination risk?
- how likely the object gets contaminated
- radioactive source is solid = no risk for object not touching source
- radioactive source is gas = could move and come into contact with object =increases risk
- gases = inhaled = contaminates on inside
When an object become contaminated, how is the irridation risk effected?
- contaminated = irradiation risk due to source = high as distance between source and object = small
Which is more longer lasting; irradiation or contamination?
- irradiation = temporary as source is taken away = stops
- contamination = lasts longer = if original source is taken away = atoms causing contamination are left behind causing more harm
How is the hazard associated with a radioactive source depends on its half life?
- lower activity of radioactive source = safer to be around
If 2 sources with diff half lives have the same number of radioactive nuclei, which will have a lower activity?
- source with longer half life will have a lower activity since the atoms are less likely to decay
If 2 sources with diff half lives have the same activity, which activity will fall faster?
- activity of sample with shorter half life= fall faster than longer half life (if same type of radiation)
- after a while = source with longer half life = higher activity = more dangerous to be around
What’s important when choosing radioactive source?
- balance between source with higher enough activity to be useful but won’t be dangerous for too long
How do tracers work and what type do radioactive isotopes are used?
- radioactive isotopes = emit gamma radiation
- injected or ingested (drunk/eaten) to see how parts of the body are working
- spread through body = progress followed on radiation detector
What type of half life do tracers need?
- relatively short (few hrs) so radioactivity in patient can quickly disappear but long enough to still emit radiation when it reaches the right place
- if too long (cancer)
What type of sources are used in medical tracer and why?
- gamma (never alpha) sources
- gamma penetrates tissue, so pass out of body and are detected
- alpha can’t and is more dangerous inside the body
Which radioisotope is absorbed by a range of organs and has a half life of over 6 hrs?
Technicium-99
How does radiotherapy work?
- radiation directed carefully at specific dosage - depends on size & type of tumour and size & age of patient= kills cancer cells without damaging too many normal cells
- a bit of damage is done = makes patient feel ill BUT if cancer is successfully killed off = worth it
How can we treat cancer externally?
- gamma rays focused on tumour using narrow beam
- patient stays still and beam is rotated round them with tumour at centre
- minimises exposure of normal cells to radiation so the damage to healthy tissue = limited
- treatment = given in doses of time = healthy cells =repaired/ replaced
How can we treat cancer internally?
- implants with beta emitters = placed next to/inside the tumour
- they damage cells in tumour BUT have short enough range = damage to healthy tissue is limited
- implant with long half life should be removed = stop radiation killing healthy cells once cancerous= killed BUT if short enough = can be left in
How can alpha emitters be used to treat cancer internally?
- alpha emitters = injected into tumour = strongly ionising = lots of damage to cancer but short range so damage to normal tissue = limited
What is nuclear fission?
- type do nuclear reaction used to release energy from large unstable nuclei by splitting them into smaller nuclei
- produces 2 smaller nuclei ( usually radioactive)and 2 or 3 neutrons
What isotope of uranium is used in nuclear fission?
Uranium - 235
But Uranium - 239 is also fissionable
What are the two ways nuclear fission can occur?
- spontaneously (unforced and happens by itself)
- by absorbing a neutron (if nucleus absorb neutron = unstable and splits)
What happens to the energy give out during nuclear fission?
- splitting = lots of energy
- some transferred to kinetic energy store or fission products
- also extra energy carried away by gamma radiation
How can nuclear fission of uranium lead to chain reaction?
- slow moving neutron is absorbed into uranium nucleus
- makes nucleus unstable =splits
- each split = spits out 2 or 3 neutrons = might be absorbed by other nuclei causing them to split too = chain reaction
What are the problems with chain reactions?
- only occurs if enough nuclei around the first
- small mass of radioactive material means that neutrons will escape = reactions stop
How do nuclear power stations use nuclear fission?
- generate electricity from chain reactions using uranium/ plutonium as fuel
- energy released = used to heat water to make steam = used to drive steam turbine connected to electricity generator
- energy transferred to surroundings by fission is greater than energy transferred in combustion reactions (coal power stations)
How are chain reactions in Nuclear power stations controlled?
- control rods
- lowered into reactor to absorb additional neutrons to slow down reactions
- nuclear bomb= no control of fission as no rods so lots of energy transferred quickly = disruptive nature
What are the problems with nuclear power and power plants?
- disposal of waste
- products of fission = highly radioactive and have long half lives
- difficult and expensive to dispose off safely
- risk of radiation leaks from plant = major catastrophes like Chernobyl
Why is the overall cost of nuclear power high?
- nuclear fuel = cheap
- overall cost = high due to cost of power plant and final decommissioning
- dismantling nuclear plant safely = takes decades
What is nuclear fusion?
- joining of 2 small atomic nuclei
- 2 light nuclei can join to create a larger nucleus which is more stable
What do 2 hydrogen nuclei form to make?
- hydrogen nucleus
Which releases more energy, fusion or fission?
- fusion releases a lot of energy
- more than fission for a given mass of fuel
- all the energy released in stars comes from fusion
Why is energy formed in fusion?
- due to difference in mass between original nuclei and new nucleus
- total mass of hydrogen nuclei is larger than mass of hydrogen nucleus
- extra mass is converted into energy and carried away by radiation
- mass of nuclei before fusion = more than mass of nucleus after fusion
Why is fusion better than fission?
- fusion doesn’t create radioactive waste
- and plenty of hydrogen to use as fuel
- people try to use fusion reactors to generate electricity
Why is the problem with fusion reactors?
- fusion only happens at really high temp - 10 000 000 degrees and high pressure
- to keep hydrogen in this = need extremely strong magnetic fields
- only few experimental reactors around (none generating electricity yet)
How does fusion happen in the sun?
- hydrogen nuclei (protons) fuse together = form larger nuclei (isotopes of hydrogen/helium)
- after more fusion reactions they make carbon,oxygen and iron
- when this happens energy is transferred form nuclear store to heating and EM radiation
Why can’t we carry out fusion in a lab?
- hard to get
- repulsion by both protons being positive has to be overcome
What happens when 2 protons fuse and hydrogen -2 and -3 fuse?
- 2 protons fuse to make = deuterium/hydrogen - 2 made
- deuterium can be fused to make tritium/hydrogen -3
- hydrogen 2 and 3 can fuse = helium nucleus and neutron (more stable than hydrogen isotopes)
What is the heaviest element made by fusion?
- Iron
- elements heavier than iron are made in a supernova
Why can fusion happen in the sun?
- high temp = increase speed of nuclei
- high Pa = keep nuclei close for fusion
How can you measure energy from fusion?
E = mc^2
Energy (J) = change in mass (kg) x speed of light ^2
Speed of light = 300 million m/s
Why does alpha and gamma gas pose as a risk?
- contamination risk of gas is higher than a solid as it can spread our and be inhaled
- alpha radiation is most dangerous inside the body and gamma is most dangerous outside the body so it could be damaging due to irradiation and contamination
Why should you keep sources as far away as possible?
- the risk of irradiation/ radiation reaching you depends on the distance from the source
- so the closer you get, the greater the risk
