A. Nuclear Forces Do nuclei contain attractive or repulsive forces? repulsion attraction

+ + A. Nuclear Forces Strong Nuclear Force (SNF) binds protons and neutrons together in the nucleus. stronger than electric repulsive force over very short distances. + +

A. Nuclear Forces Effect of Size on Stability Small Nucleus SNF is relativity static more protons, more electric repulsion larger, more unstable (↑ 82 protons) Small Nucleus Large Nucleus attraction repulsion attraction repulsion

B. Nuclear Reactions Transmutation + change of an atom of one element (atom) to an atom of different element identity changes by changing # of PROTONS (At #) nuclear reactions can change nuclei and proton # (Atomic #) to make different atoms chemical reactions transfer or share electrons to rearrange atoms +

E = mc2 B. Nuclear Reactions Nuclear Binding Energy 3.00 x 108 m/s!!! the energy released when a nucleus is formed during fusion or when nuclei are formed during fission. little mass converted to LOTS of energy E = mc2 3.00 x 108 m/s!!!

Nuclear Fission of Uranium-235 B. Fission splitting a larger nucleus into smaller (daughter) nuclei and/or particles. (Nuclear Power Plants use this) Nuclear Fission of Uranium-235

An aside definition: A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is an atom that has excess nuclear energy, making it unstable. This excess energy will normally be emitted from the nucleus as radiation.

Nuclear Fission of Uranium-235 B. Fission Nuclear Fission of Uranium-235

A fission chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events. Positive feedback is usually generated by neutron production and moderation. A neutron moderator is a medium that reduces the speed of neutrons so they can be used in a nuclear reaction involving uranium-235 or a similar fissile nuclide. A neutron absorber is a medium that removes neutrons from the chain reaction process

B. Fission Storage of Radioactive Waste spent fuel rods in water pools (short term) or dry casks of concrete/steel (long term).

C. Fusion combining of 2 nuclei to form 1 larger nucleus is the “typical” product much more energy powers stars naturally high temp plasma

Tokamak Fusion Test Reactor C. Fusion Fusion reactors (not sustainable, very hard to keep going) Tokamak Fusion Test Reactor

C. Fission vs Fusion Fission Fusion vs. FISSION FUSION 235U is limited meltdown risk radioactive waste less energy Hydrogen is abundant no meltdown risk harmless product not yet sustainable

Coming up: Writing Nuclear Reactions Nuclear Decay Rate Calculations

Quick Quiz. E=mc2 shows how a little bit of _________ can be converted into lots of __________. energy, mass. mass, energy. mass, light. light, energy. 15

Quick Quiz. Which statement about nuclear reactions is FALSE? Heat and light in the sun are produced by hydrogen fusion reactions. The total mass of the products is slightly less than the total mass of the reactants. In fusion, nuclei are combined, and in fission, nuclei are split. Power plants use fusion of H isotopes. 16