Topic 12 - Particle Physics

Question 1

Nuclear fission

Answer 1

The process by which a large, unstable nucleus splits into two smaller daughter nuclei, releasing energy

Question 2

Nuclear fusion

Answer 2

The process by which two atomic nuclei join to make a large nucleus, releasing energy (more than fission). The smaller nuclei lose mass, and the lost mass becomes KE.

Question 3

Radioactive decay

Answer 3

An unstable nucleus becoming more stable over time by randomly emitting ionising radiation

Question 4

Fission of Uranium-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

Chain reaction

Answer 5

​The process of neutrons released by a fission reaction being absorbed by another unstable, large nuclei, and inducing further fission

Question 6

Role of moderator in fission process

Answer 6

Absorbs some of the kinetic energy of the neutrons to slow them down to sustain a chain reaction. Slow neutrons are more easily absorbed by unstable nuclei.

Question 7

Role of control rods in fission process

Answer 7

Can be lowered to absorb neutrons to completely remove them from the fission process and control the rate of fission

Question 8

Role of shielding around a nuclear reactor

Answer 8

Shielding materials absorb hazardous radiation as daughter nuclei formed and neutrons emitted from fission are radioactive.

The reactor is surrounded by a 2m thick steel and concrete wall

Question 9

Energy source for stars

Answer 9

nuclear fusion

Question 10

Conditions for nuclear fusion

Answer 10

• 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
• high gas density