Radioactivity and Particles - Fission and Fusion

Question 1

what is nuclear fission?

Answer 1

the process where heavy atoms are split into smaller, lighter atoms. this releases energy

Question 2

what is nuclear fusion?

Answer 2

the process where lighter atoms are forced to join together to make heavier atoms. this releases energy
mass before > mass after

Question 3

how is radioactive decay a source of energy?

Answer 3

within the core of the earth, radioactive isotopes of elements such as uranium, thorium and potassium provide a large proportion of the heat within the earth through radioactive decay.

Question 4

what happens during the fission of U-235?`

Answer 4

• a slow moving neutron is absorbed by a uranium 235 nucleus
• the resulting uranium 236 nucleus is unstable
• it splits to form two smaller daughter nuclei, three neutrons and gamma radiation.

Question 5

how does a chain reaction happen?

Answer 5

• the three neutrons produced by the fission may hit other nuclei of uranium 235, causing the process to repeat
• for a chain reaction to occur, there is a minimum mass of uranium 235 required, this is the critical mass

Question 6

what is a moderator?

Answer 6

• graphite is used as a moderator.
• the purpose of the moderator is to absorb some of the kinetic energy of the neutrons to slow them down
• this is because slow neutrons are more easily absorbed by uranium 235 nuclei.

Question 7

what are control rods?

Answer 7

• made of boron or cadmium.
• the purpose of the control rods is to absorb neutrons and completely remove them from the fission process.
• helps adjust the rate of nuclear fission in the reactor

Question 8

what is the role of shielding around a nuclear reactor?

Answer 8

• the reactor vessel is made of steel and surrounded by a concrete layer about 5 meters thick
• this prevents any radiation from escaping, even neutrons

Question 9

what is the difference between nuclear fusion and nuclear fission?

Answer 9

• fission: larger nuclei are split into smaller nuclei
• fusion: two smaller nuclei collide and combine to form a larger nucleus

Question 10

where is nuclear fusion used?

Answer 10

• nuclear fusion is the source of energy for our sun and all stars
• in the case of the sun, it is typically hydrogen undergoing fusion to create helium

Question 11

why does nuclear fusion not happen at low temperatures and pressures?

Answer 11

• for nuclear fusion to occur, very high temperatures are required to overcome the repulsive force between the positively charged nuclei of each isotope
• high pressures are also needed to increase the chance of fusion between the nuclei