Radiation And Space Y11

Question 1

Why does radiation occur?

Answer 1

Some nuclei are unstable and undergo radioactive decay to make themselves more stable

Question 2

What is alpha decay?

Answer 2

• 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

Question 3

What is beta decay?

Answer 3

• 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

Question 4

What is gamma decay?

Answer 4

• 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

Question 5

What is radioactivity measured in?

Answer 5

Bequerels (Bq)

Quantity of radioactive material which 1 nucleus decays per second

Question 6

How can we calculate how much of a sample has decayed?

Answer 6

• 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

Question 7

How do you calculate how much is left after a half life?

Answer 7

After n half lives 1-(1/2)^n has decayed

(1/2)^n remains

Question 8

How does carbon dating work?

Answer 8

• 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)
1:10m (alive)
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

Question 9

How does rock dating work?

Answer 9

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

Question 10

How do we measure ionising radiation?

Answer 10

With a photographic film of a Geiger-muller tube

Question 11

Where does background radiation come from?

Answer 11

• artificial(15%):
Medical x-rays, radioactive waste from power plants, radioactive fallout from nuclear weapons testing
• natural:
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

Question 12

How does nuclear fission work?

Answer 12

• 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

Question 13

What do the control rods in a nuclear reactor do?

Answer 13

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

Question 14

What is the water for in a nuclear reaction?

Answer 14

• 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

Question 15

What do the fuel rods do?

Answer 15

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

Question 16

Why is the nuclear reactor encased in a thick steel case, and then a concrete canister?

Answer 16

Steel case: keeps water at high pressure to stop it boiling

Concrete canister: stops gamma radiation escaping an harming workers

Question 17

What are the safety controls of the nuclear reactor?

Answer 17

• 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

Question 18

What are the dangers of radiation?

Answer 18

• 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

Question 19

What was the old model of the atom?

Answer 19

• plum pudding model

* sphere of positive charge w amount of negative charge dotted over the place to make it neutral

Question 20

What happened in the Geiger and Marsden experiment?

Answer 20

• 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

Question 21

What did they expect to happen? What results did they get? Why was this weird?

Answer 21

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

Question 22

What was the new model? How did it explain the results?

Answer 22

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

Question 23

How can radioactivity be used in monitoring thickness?

Answer 23

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

Question 24

How can radioactivity be used in finding leaks?

Answer 24

• 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

Question 25

How can radioactivity be used medically?

Answer 25

• 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

Question 26

What is the effect of gravity on the universe?

Answer 26

It causes satellites to orbit the earth, moons to orbit planets, planets to orbit the sun, and comets to orbit the sun

Question 27

What do the orbits of comets/planets/moons look like?

Answer 27

• 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

Question 28

What is the equation for orbital speed?

Answer 28

Orbital speed = (2 x pi x orbital radius) / time period

Question 29

What is the universe?

Answer 29

A large collection of billions of galaxies

Question 30

What is a galaxy? What galaxy are we in?

Answer 30

• a galaxy is a large collection of billions of stars

* our solar system is in the Milky Way galaxy.