Nuclear Fission and Nuclear Fission and FusionFusion

Unit 8 – Part BUnit 8 – Part B

Nuclear BalanceNuclear Balance

Delicate balance between attractive strong Delicate balance between attractive strong nuclear forces and repulsive electric nuclear forces and repulsive electric forces.forces. In all nuclei the strong nuclear forces In all nuclei the strong nuclear forces

dominate.dominate. But in heavier nuclei this is lost and decay But in heavier nuclei this is lost and decay

occursoccurs

Nuclear FissionNuclear Fission

Nuclear Fission:Nuclear Fission: The splitting of a heavy The splitting of a heavy nucleus into two lighter nuclei, nucleus into two lighter nuclei, accompanied by the release of a lot of accompanied by the release of a lot of energy.energy. A neutron is shot at the nucleus and A neutron is shot at the nucleus and

elongates the nucleus disrupting the strong elongates the nucleus disrupting the strong nuclear force.nuclear force.

The energy released is in the form of Kinetic The energy released is in the form of Kinetic Energy.Energy.

Nuclear FissionNuclear Fission

Nuclear FissionNuclear FissionChain Reaction:Chain Reaction: A self-sustaining A self-sustaining reaction in which the products of one reaction in which the products of one fission event stimulate further events.fission event stimulate further events.

Nuclear FissionNuclear Fission

Nuclear Fission Bomb:Nuclear Fission Bomb: Critical Mass:Critical Mass: The minimum mass of The minimum mass of

fissionable material needed in a reactor or fissionable material needed in a reactor or nuclear bomb that will sustain a chain nuclear bomb that will sustain a chain reaction.reaction.

If a reaction occurs where there is enough If a reaction occurs where there is enough space for neutrons to escape, the reaction space for neutrons to escape, the reaction quits.quits.

If a reaction occurs where the neutrons If a reaction occurs where the neutrons continue to collide, energy builds up, causing continue to collide, energy builds up, causing mass to exceed the critical mass.mass to exceed the critical mass.

Nuclear Energy Comes from Nuclear Energy Comes from Nuclear MassNuclear Mass

Individual nucleons have the most mass in Individual nucleons have the most mass in the lightest nuclei.the lightest nuclei. Combined nucleons inside a nucleus have a Combined nucleons inside a nucleus have a

smaller mass than individual nucleons.smaller mass than individual nucleons. The greater the mass of the nucleon, the The greater the mass of the nucleon, the

greater amount of energy needed to pull the greater amount of energy needed to pull the nucleons apart from each other.nucleons apart from each other.

Nuclear Energy Comes from Nuclear Energy Comes from Nuclear MassNuclear Mass

Carbon-12 atom – (nucleus has 6 protons Carbon-12 atom – (nucleus has 6 protons and 6 neutrons).and 6 neutrons). Mass exactly 12.00000 atomic mass units Mass exactly 12.00000 atomic mass units

(amu)(amu)

Individual Proton – 1.00728 amuIndividual Proton – 1.00728 amu

Individual Neutron – 1.00867 amuIndividual Neutron – 1.00867 amu 6 Protons (6x1.00728) + 6 Neutrons 6 Protons (6x1.00728) + 6 Neutrons

(6x1.00867)=(6x1.00867)= 12.09570 amu12.09570 amu

Nuclear Energy Comes from Nuclear Energy Comes from Nuclear MassNuclear Mass

Remember that Remember that EnergyEnergy is the ability to do work. is the ability to do work. Work = force x distanceWork = force x distance

A great deal of force is required to pull a A great deal of force is required to pull a nucleon out of a nucleus.nucleon out of a nucleus. Needed to overcome the attractive strong nuclear Needed to overcome the attractive strong nuclear

force.force.

The work done on the nucleon is energy that is The work done on the nucleon is energy that is added to the nucleon.added to the nucleon. Shows up as additional mass.Shows up as additional mass.

Nuclear Energy Comes from Nuclear Energy Comes from Nuclear MassNuclear Mass

The average mass per nucleon is key to The average mass per nucleon is key to understanding the energy released.understanding the energy released. (Divide the total (Divide the total

mass of a nucleus mass of a nucleus

by the number of by the number of

nucleons in the nucleons in the

nucleus) nucleus)

Nuclear PowerNuclear Power

Einstein’s Equation: e = mcEinstein’s Equation: e = mc22.. Energy = (Mass) x (Speed of light)Energy = (Mass) x (Speed of light)22

Helps us understand how energy is released Helps us understand how energy is released in nuclear reactions.in nuclear reactions.

There is less mass after splitting than There is less mass after splitting than before.before. The “missing” mass is converted to energy.The “missing” mass is converted to energy.

Nuclear FusionNuclear FusionNuclear Fusion:Nuclear Fusion: The joining together of The joining together of light nuclei to form a heavier nucleus, light nuclei to form a heavier nucleus, accompanied by the release of a lot of accompanied by the release of a lot of energy.energy.

Promising future ofPromising future of

nuclear energy nuclear energy

because the lack of because the lack of

radioactive waste.radioactive waste.

Nuclear FusionNuclear Fusion

If two small nuclei were to fuse, such as If two small nuclei were to fuse, such as two nuclei of Hydrogen, the mass of the two nuclei of Hydrogen, the mass of the fused nucleus, Helium, would be less than fused nucleus, Helium, would be less than the total mass of the two Hydrogen nuclei.the total mass of the two Hydrogen nuclei.

The lost mass is converted into useful The lost mass is converted into useful energy.energy.

Nuclear PowerNuclear Power