Flashcards in Radiation And Space Y11 Deck (30)
Why does radiation occur?
Some nuclei are unstable and undergo radioactive decay to make themselves more stable
What is alpha decay?
• alpha particle ejected from nucleus
• made of 2 protons and 2 neutrons
• 10% speed of light
• 5-8cm range, stopped by thin piece of paper
• highly ionising
• atomic mass - 4
• atomic number - 2
What is beta decay?
• neutron turns into proton and electron
• proton stays but electron ejected
• up to 90% speed of light
• 5-10cm range, stopped by alfoil
• less ionising
• same atomic mass
• atomic number + 1
What is gamma decay?
• nucleus, even after a or b decay can still be a bit energetic ∴ releases a gamma ray yo lose energy and become stable
• high grew, high energy em wave
• no structure/mass/charge
• trials at speed o' light, readuced by lead and concrete
• Addley ionising
What is radioactivity measured in?
Quantity of radioactive material which 1 nucleus decays per second
How can we calculate how much of a sample has decayed?
• you can't- decay is random, but we can use stats to analyse
• measure in half lives, as the substance never fully decays
Half live = time taken for num f nuclei to halve OR time taken for activity of a sample to halve
How do you calculate how much is left after a half life?
After n half lives 1-(1/2)^n has decayed
How does carbon dating work?
• two isotopes: Carbon 12 and carbon 14
• neutrons from cosmic rays in space react w nitrogen to form carbon 14, and also a proton and electron
• this is always happening ∴ rate remains constant
• when organism dies c12 remains but C14 decays ∴ ratio changes
E.g. Ratio of C14 :C12 in living things is 1:10m. An axhandle has a ratio 1:80m. How old is it? (C14 half life = 5700yrs)
0.5 :10m (1 half life)
0.25:10m (2 half lives)
0.125:10m (3 half lives)
1:80m (3 half lives) ∴ 5700x3 =17100yrs
How does rock dating work?
We can date using ratio of parent radioactive isotopes which decay into more stable daughter isotopes
Relative proportions of nuclei give us rock's age
Age of rock after n half lives: 1:2^n-1
How do we measure ionising radiation?
With a photographic film of a Geiger-muller tube
Where does background radiation come from?
Medical x-rays, radioactive waste from power plants, radioactive fallout from nuclear weapons testing
Cosmic rays- reaches earth from space
Some rocks and soil release radioactive radon gas
Living things- plants absorb radioactivity from soil and these pass up food chain
How does nuclear fission work?
• large nucleus turns into two smaller nuclei
• happens when a neutron is absorbed and the nucleus becomes v excited
• KE, 2 daughter nuclei, and some neutrons are released
• the neutrons then cause a chain reaction if they hit other nuclei
• but if one one neutron us absorbed each time then fission continues at a constant rate, called criticality
What do the control rods in a nuclear reactor do?
Chain reaction must happen at a steady rate tf we need control rods to control the speed of reaction. Made of boron which absorbs neutrons.
If lowered ⇒ reaction slower
If taken out ⇒ reaction faster
What is the water for in a nuclear reaction?
• the neutrons must be moving slowly to be captured by the U nuclei so they can for a chain reaction
• the water acts as a moderator to slow down the neutrons ∴ making it easier for them to be captured
• also used as a coolant to remove the heat produced by the nuclear reactions ∴ can heat up the other separate water system to power a steam generator
What do the fuel rods do?
Made of U 235
Produce lots of heat in the reactions ∴ warm up the coolant
Need to be replaced every 3 years as less efficient due to waste products
Why is the nuclear reactor encased in a thick steel case, and then a concrete canister?
Steel case: keeps water at high pressure to stop it boiling
Concrete canister: stops gamma radiation escaping an harming workers
What are the safety controls of the nuclear reactor?
• in emergency, control rods can shut down reactions
• waste products v radioactive. Encased in glass and disposed of deep underground
• backup system ensured coolant flowing at all times or system will overheat
What are the dangers of radiation?
• can cause mutations in DNA
• can damage cells and tissues
In body: a most dangerous as easily absorbed. B and g less dangerous as likely to pass through cells
If outside body: a least dangerous as not likely to reach cells inside., but b and g more dangerous as can penetrate through tissues
What was the old model of the atom?
• plum pudding model
• sphere of positive charge w amount of negative charge dotted over the place to make it neutral
What happened in the Geiger and Marsden experiment?
• a particles shot at v thin pice of gold foil
• a detector made of fluoro material emitted a flash of light whenever a a particle hit it
∴ you could determine path of a particle
What did they expect to happen? What results did they get? Why was this weird?
Expected: most a particles pass straight through foil, but some deflect at small angles
Actual: most passed straight through some deflected at large angled, 1/8000 rebounded
Inconsistent: in PP model mass is distributed throughout atom ∴ atom not dense enough for a large force to be achieved ∴ a particles can't rebound
What was the new model? How did it explain the results?
Atom has tiny positive nucleus, contains all the mass, orbited by electrons. Rest is empty space
The rebounding particles are caused by head on collisions w the nucleus. Since both are positive repulsion occurs w big force
Deflection is when particles come near nucleus and they repel each other due to positive. Closer they come, bigger repulsion ∴ bigger angle of deflection.
Most particles pass through empty space ∴ no deflection
However, if the electrons did orbit the nucleus, they'd spiral in towards it ∴ the atoms would be inherently unstable
How can radioactivity be used in monitoring thickness?
lace a radioacitve source over a GM tube, with what you are measuring in the middle. Have rollers to control the thickness at either end.
If paper too thick, not enough particles will reach GM tube as blocked by paper ∴ signal to rollers make it thinner
If paper too thin, vice versa
Can't be a particles, as they are blocked by most things, and no g as wouldn't be blocked at all
Need long half life, as if too short, couldn't tell if change in count due to thickness or decay due to age
How can radioactivity be used in finding leaks?
• radioactive material injected into pipe
• GM tube on surface can detect high levels of radiation, which will be where it is leaking
• must be g to penetrate surface, as a or b would be absorbed
• must be non-toxic
How can radioactivity be used medically?
• can use radiation to kill cells not working properly, e.g. Cancer. Tracer should emit b or a , as they interact w cells and have half life of a few hours
• radioactive subs can also be attached to biochemicals, called tracers
• after injection person can be put under a gamma camera to show how organs are functioning. Use g rays so radiaction can escape body wo interacting w it ∴ min damage
• half life of a few hrs so drug can move around body, but not so person is radioactive for long time
What is the effect of gravity on the universe?
It causes satellites to orbit the earth, moons to orbit planets, planets to orbit the sun, and comets to orbit the sun
What do the orbits of comets/planets/moons look like?
• comets have a highly elliptical orbit
• planet have orbits that are elliptical, but nearly circular, apart from Pluto
• moons have orbits that are elliptical but nearly circular
What is the equation for orbital speed?
Orbital speed = (2 x pi x orbital radius) / time period
What is the universe?
A large collection of billions of galaxies