E = mc2 If you can’t explain it simply, you haven’t learned it well enough. Einstein

Special Theory of Relativity Albert Einstein’s Special Theory of Relativity Einstein said energy and mass are equivalent in his famous equation: E = mc2 E is energy, m is mass and c is the speed of light in a vacuum (3x 108 m/s) During nuclear reactions, small amounts of mass are converted into energy To compare, 1 gram of TNT produces 2931 J of energy When one gram of matter is converted into energy: E = (0.001 kg) x (3 x 108 m/s)2 or E = 90,000,000,000,000 J!

Mass and energy together are always conserved. Albert Einstein’s Special Theory of Relativity Einstein modified the Law of Conservation of Energy to include nuclear reactions: Mass and energy together are always conserved.

Why are some nuclei unstable? In larger nuclei, there is greater distance between protons and neutrons. At a greater distance, the strong nuclear force becomes weaker. Therefore the repulsive electric forces among + protons forces nucleus to break apart (decay). Half-Life – the time it takes half of the radioactive atoms in a sample to decay. Half-lives range from seconds to billions of years. Uranium-238 has a half-life of 4.5 billion years.

Nuclear Reactions Neutron Fission of Uranium-235 Nuclear Fission – process of splitting an atomic nucleus into smaller parts The chain reaction releases large amount of energy that can be used to generate electricity or destroy cities (bomb!) Drawback: Radioactive Waste

FISSION Uranium is the principle element used in nuclear reactors and in certain types of atomic bombs. The specific isotope used is 235U. When a stray neutron strikes a 235U nucleus, it is at first absorbed into it. This creates 236U. 236U is unstable and this causes the atom to fission. The fissioning of 236U can produce over twenty different products. However, the products' masses always add up to 236. The following two equations are examples of the different products that can be produced when 235U fissions: 235U + 1 neutron 2 neutrons + 92Kr + 142Ba + ENERGY 235U + 1 neutron 2 neutrons + 92Sr + 140Xe + ENERGY

Nuclear Fission Chain Reaction

What does it mean if something is radioactive? Radioactive atoms have unstable nuclei and become more stable by breaking down (radioactive decay) The nucleus of one atom becomes the nucleus of another less massive atom by emitting radiation (particles or rays of energy) There are 3 common types of nuclear radiation 1. Alpha Decay – emission of positively charged particle (helium nucleus) 2. Beta Decay – emission of electron by nucleus when neutron decomposes 3. Gamma Decay – emission of high energy electromagnetic radiation

Splitting the Uranium Atom:

A Chain Reaction

Nuclear Radiation Radiation can damage cells and tissues of your body and ionize atoms in your body It can damage DNA and lead to CANCER Alpha particles can be blocked by a piece of paper or clothing Beta particles can be blocked by sheet of aluminum Gamma rays can be blocked by meters-thick concrete or cms-thick lead, and is the most penetrating.

Radon in Homes

Nuclear Fission – Nuclear Reactors (Controlled Fission)

Nuclear Fission – Atomic Bomb (Uncontrolled Fission) http://www.youtube.com/watch?v=Xs3JE4WRL-8&feature=related

The Proton-Proton Reaction: In our Sun, fusion reactions occur in the central region, where the density is increased to 100 times the density of water on Earth, sending temperatures to about 15 million K (27,000,000 degrees F). At these temperatures, the hydrogen is ionized, or stripped of their electrons, creating a plasma of free electrons and protons (the nuclei of hydrogen). The heat provides enough energy for the hydrogen ions to collide with enough force to overcome the repulsion between these positively charged nuclei and fuse them together.

One of the resulting two protons that just fused decays into a neutron, forming a deuteron. The decay process also releases an anti-electron, or positron, and a neutrino. The positron will later collide with an electron and annihilate each other, releasing two gamma rays, which are high-energy photons. The neutrino interacts very weakly with matter, and will pass right out of the sun. The newly formed deuteron (2H) may collide into another hydrogen nucleus, creating the helium isotope 3He and causing the release of a gamma ray. When two of these 3He isotopes collide, two of its protons are released, creating 4He.

Nuclear Reactions Nuclear Fusion – process that releases energy when lighter nuclei combine to form heavier nuclei Occurs naturally in all stars Responsible for giving off light and heat! Problems generating fusion on Earth: HIGH temperatures and pressure and containment!

Nuclear Fusion - Sun