P20: Energy from the Nucleus

Question 1

Nuclear Fission

Answer 1

The process in which certain nuclei (uranium-235 and plutonium 239) split into two ‘fragment’ nuclei as a result of absorbing a neutron, releasing energy and two or three neutrons as a result. (chain reaction).

Question 2

Fission Neutrons

Answer 2

Neutrons released during fission, which travel at high speed and also catalyse other Fission Reactions.

Question 3

What three things are produced by Nuclear Fission?

Answer 3

> Fragment Nuclei
Fission Neutrons: 2-3.
Energy in the form of radiation, and the kinetic energy of the fission neutrons and fragment nuclei.

Question 4

Nuclear Fission Reactor

Answer 4

> A reactor that releases energy steadily due to the fission of a suitable isotope such as Uranium-235.
This isotope is suitable because exactly one Fission Neutron from each reaction goes on to catalyse another reaction, keeping the rate of energy production steady.

Question 5

Features of the inside of a Nuclear Reactor

Answer 5

> Water is added as a moderator (to slow down the uranium atoms so that they can cause further fission) and a coolant (to absorb kinetic energy from the neutrons and feel rods).
Control Rods: Absorb surplus neutrons (keeps the chain reaction under control).
Reactor Core: Made of thick steel to withstand high temps and pressures. Surrounded by concrete shield to absorb any escaping radiation.

Question 6

Fission

Answer 6

Splitting.

Question 7

Fusion

Answer 7

Joining.

Question 8

Nuclear Fusion

Answer 8

The process in which small nuclei are forced together so they fuse with each other to form a larger nucleus.

Question 9

Fusion of Hydrogen -> Helium

Answer 9

1. Two protons (hydrogen nuclei), collide and react to form ‘Heavy Hydrogen’ (2/1 H).
2. 2 Protons collide with 2 of these Hydrogens, and turn them into heavier nuclei.
3. The two heavier nuclei collide to form 4/2 He.
4. The energy produced at every stage is carried away as kinetic energy.

Question 10

Plasma in a Fusion Reactor

Answer 10

> Plasma is heated by passing a large electric current through it.
It is contained by a magnetic field so that it doesn’t touch the reactor walls, which would make it go cold.
If the fusion worked, it would create more energy than it takes to heat the plasma.

Question 11

Problems of Fusion Reactors.

Answer 11

> Plasma has to be very hot to be able to overcome the repulsion force between two positive nuclei.
Not yet developed.

Question 12

Positives of Fusion Reactors.

Answer 12

> Fuel for fusion is Heavy Hydrogen- abundant in sea water.
Reaction product, helium, is non-reactive and harmless.
Much better than fission reactors.

Question 13

Sources of Background Radiation

Answer 13

> Cosmic Rays
> Food and Drink
> Medical Treatments (e.g X-rays)
> Air Travel
> Ground and Buildings
> Natural Radioactivity in the Air.
> Nuclear weapons Testing.
> Nuclear Power.

Question 14

Radon Gas

Answer 14

> Seeps through the ground from radioactive rocks buried deep underground.
Emits alpha particles, hazardous if breathed in.
Can seep into buildings etc. in areas where it is abundant.
Combated with special suction pumps underground.

Question 15

Effect of Alpha radiation from a source outside the body.

Answer 15

Very dangerous- Affects all surrounding tissue.

Question 16

Effect of Alpha radiation from a source inside the body.

Answer 16

Possible Danger- absorbed by skin, can damage skin + retina cells.

Question 17

Effect of Beta and Gamma Radiation from a source inside or outside of the body.

Answer 17

Dangerous- Can reach cells throughout the body without having to be ingested.

Question 18

How long ago did the Big Bang take place?

Answer 18

13 Billion years ago.

Question 19

How has the universe changed since the big bang?

Answer 19

> It began as a hot glowing ball of radiation and matter.

> Now, it is cold and dark except for the hot spots caused by stars.

Question 20

Features of the Dark Age of the Universe.

Answer 20

> As the universe expanded, it became transparent as radiation passed through the empty space between its atoms.
Microwave Background Radiation was released at this stage.
The universe was a dark, patchy cloud of hydrogen and helium.
Slowly, the denser parts of the universe began to attract the surrounding matter, and the universe became even more patchy.
Eventually, gravity drew these clumps into galaxies, and the stars lit up the universe.

Question 21

What do stars form out of?

Answer 21

Clouds of Dust and Gas

Question 22

Protostar

Answer 22

> The Concentration of dust clouds and gas in space that goes on to form a star.
The dust and gas are drawn together by their own gravitational force.

Question 23

What happens if a Protostar gets hot enough?

Answer 23

> The nuclei of hydrogen and all of the light elements fuse together, releasing energy which causes it to get hotter and brighter- a star is born.

Question 24

What happens to Protostars that don’t get hot enough for fusion to take place?

Answer 24

They may be attracted by another, larger protostar’s gravitational force and become planets.

Question 25

Main Sequence Stars

Answer 25

> Main stage in a star's lifecycle. > Energy released from fusion allows more fusion to take place. > Radiation flows out steadily. > Stable- the forces within it are balanced.

Question 26

What forces keep a main sequence star balanced?

Answer 26

> Gravity makes the star contract. | > The radiation from the core makes the star expand.

Question 27

Red Giant

Answer 27

> A main sequence star smaller than our sun that has swelled out, cooled down and turned red. > At this stage the light elements start to fuse to create heavier elements.

Question 28

What happens when a Red Giant runs out of light elements for fusion?

Answer 28

> No more radiation is released. > Because of the star's own gravity, it collapses in on itself. > As it collapses, it heats up and turns from red- yellow- white. (White Dwarf)

Question 29

White dwarf

Answer 29

A star that has collapsed after the Red Giant stage and has become much hotter and denser that it was.

Question 30

Black dwarf

Answer 30

A star that has faded out and gone cold.

Question 31

Lifecycle of a small star

Answer 31

``` Protostar Main Sequence Red Giant White Dwarf Black Dwarf ```

Question 32

Red Supergiant

Answer 32

> A star much larger than the sun will swell out after the main sequence stage to become a red supergiant before it collapses. > This happens because it has run out of light elements to use in fusion.

Question 33

What happens when a Red Supergiant collapses?

Answer 33

> The matter surrounding the core compresses the core more and more. > Then the compression suddenly reverses in a supernova.

Question 34

Supernova

Answer 34

The explosion of a massive star after fusion in its core stops and the matter surrounding the core collapses onto the core and rebounds.

Question 35

What happens after a supernova.

Answer 35

> The core of the star is compressed until it becomes a neutron star (made entirely of neutrons). > If the stare is big enough, it becomes a black hole instead.

Question 36

Black Hole

Answer 36

The extremely compressed core of a star that has so much mass that nothing, not even light, can escape its gravitational field.

Question 37

How are light elements formed?

Answer 37

In fusion in a star's core. When a star becomes a red giant it starts to fuse lighter elements up to iron. Anything larger than iron can't be formed in this process because it requires too much energy.

Question 38

How are heavy elements formed?

Answer 38

> When a massive star collapses and then explodes as a supernova. > The enormous force first fuses them and then propels them into space. > Because planets form out of the elements found around a newly formed star, planets contain all of the known elements.