2.6 Nuclear Fission and Nuclear Fusion

Question 1

What are the 2 fissionable substances?

Answer 1

Uranium-235 and plutonium-239

Question 2

What is nuclear fission?

Answer 2

The splitting of an atomic nucleus

Question 3

How is nuclear fission started?

Answer 3

The fissionable atom must abosorb a neutron

Question 4

What happens when a fissionable substance absorbs a neutron?

Answer 4

1. The nucleus splits into 2 smaller nuclei
2. 2 or 3 neutrons are released
3. Energy is released

Question 5

What is nuclear fusion?

Answer 5

The joining of two nuclei to form a larger one

Question 6

Where does nuclear fusion occur naturally?

Answer 6

Stars

Question 7

How is a protostar made?

Answer 7

1. The first stage of a star
2. Clouds of gas and dust sprial together due to gravity

Question 8

How is a main sequence star made?

Answer 8

1. Made from a protostar
2. Gravitational energy is converted to heat energy so the temperature rises
3. When the temperature gets high enough, hydrogen nuclei undergo nuclear fusion to give out heat and light
4. This maintains its energy output for billions of years due to the massive amounts of hydrogen

Question 9

How is a red giant made?

Answer 9

1. Made from a main sequence star that’s the same size as the sun
2. When the hydrogen runs out, heavier elements are made from the nuclear fusion of helium
3. The star swells, it becomes red and the surface cools

Question 10

How is a white dwarf made?

Answer 10

1. Made from a red giant
2. The red giant becomes unstable and ejects its outer layer of dust and gas as a planetary nebula
3. A hot, dense solid core is left behind - white dwarf
4. This cools down to a black dwarf and eventually dissapears

Question 11

How is a red super giant made?

Answer 11

1. Made from main sequence stars that are much bigger than the sun
2. Heavier elements are made such as iron
3. Eventually it explodes in a supernova, this forms elements heavier than iron
4. These elements are ejected into the universe to form new plants and stars

Question 12

How is a neutron star made?

Answer 12

1. Made from a red super giant
2. When the red super giant explodes, a very dense core is left called a neutron star

Question 13

How is a black hole made?

Answer 13

1. Made from a red super giant
2. When the red super giant explodes it leaves behind its core
3. If the star is big enough it will become a black hole