Fission and Fusion Physics 12 Adv

Nuclear Particles As we discussed, the nuclear particles are composed of quarks; the individual particles are the result of three quarks held together by the strong force When three different “colour” quarks are combined, the strong force is mostly contained within the particle; the remaining strong force holds the nucleus together

Strong Force The strong force acts in two different ways:  To contain quarks; in this instance it increases with separation and as a result of this property, isolated quarks cannot be observed  To bind the nucleus; in this instance it acts over a very small distance but instead this distance, it is much larger than electrostatic forces

Protons, Neutrons and Electrons The atom is composed of three subatomic particles: ParticleCharge (in C) SymbolMass (in kg) Electron-1.602x e-e x Proton1.602x p+p x Neutron0n0n x10 -27

Atomic Mass Unit (u) When dealing with nucleons, it is often more useful to deal with mass in Atomic Mass Units (u) instead of kilograms ParticleMass (in kg) Mass (in u) Electron x Proton x Neutron x

The electron volt (eV) Since the energies involved in nuclear physics are so small, instead of using joules to describe energy, the electron volt is used instead One electron volt is equal to 1.60x J

Atomic Nucleus Atom described using:  X – atomic symbol  A – atomic mass number (nucleon number)  Z – atomic number Number of protons and electrons = Z Number of neutrons = A - Z

Stability and the Nucleus Although the “Strong Nuclear Force” is strong enough to hold a small nucleus together, as the size of the nucleus becomes larger, the electrostatic forces begin to become more important As a result, if we consider various nuclei based on their Atomic Number and Neutron Number we get the following result:

Nuclides and Isotopes Nuclides are different combinations of nucleons Isotopes occur when an element (specific Atomic Number) has different numbers of neutrons (different Atomic Mass Numbers) For example, there are three common isotopes of hydrogen:

Nuclear Binding Energy It takes 13.6eV to separate an electron from a hydrogen atom However, it takes more than 20MeV to separate a neutron from a helium-4 atom The energy to separate all the nucleons in a nucleus is called the binding energy

Fusion When highly energetic small nuclei (smaller than iron) collide, there is a probability that fusion will occur In a high energy nuclear collision, the two nuclei are moving quickly so that they approach closely enough that the strong force overcomes the electrostatic forces and a new nucleus is formed

Where Does the Energy Come From? In order to find where the energy in a fusion reaction comes from, it is necessary to turn to Einstein’s mass-energy equivalence equation: Since mass and energy are equivalent, when energy is released, mass is lost and when mass is created, energy is lost

Sample Fusion Reaction Deuterium and tritium (hydrogen isotopes) undergo a nuclear fusion reaction to produce helium, a neutron and 17.6MeV of energy We can track the energy involved if we know the masses of each nuclei

Sample Fusion Reaction Deuterium has a mass of u Tritium has a mass of u Helium has a mass of u A neutron has a mass of u Determine the mass defect (loss of mass) during the reaction

Sample Fusion Reaction Mass of deuterium & tritium – u Mass of helium & neutron – u Mass defect – u

Sample Fusion Reaction Using Einstein’s mass-energy equivalence equation, we see:

Sample Fusion Reaction Therefore, this reaction should release MeV of energy

Layers of a Star In a star, as heavier elements are formed they move toward the middle of the star while the lighter elements are toward the outside Not all elements are present as some fusion reactions are transitory

Problem Analyze the solar fusion chain which is composed as follows: