2. Section 24-3 Nuclear Fission Stability of elements is best around a mass number of 60. Atoms with a mass number greater than 60 tend to gain stability by fragmenting. The splitting of nuclei into fragments is known as nuclear fission.nuclear fission Fission is accompanied with a very large release of energy.

3. Section 24-3 Nuclear Fission Nuclear power plants use fission to produce electricity by striking uranium-235 with neutrons.

4. Section 24-3 Nuclear Fission (cont.) Each fission of U-235 releases three additional neutrons. Each of those neutrons can release three more neutrons. The self-sustaining process is called a chain reaction. http://glencoe.mcgraw- hill.com/sites/007874637x/student_view0/chapter24/concepts_in_motio n.htmlhttp://glencoe.mcgraw- hill.com/sites/007874637x/student_view0/chapter24/concepts_in_motio n.html

5. Section 24-3 Nuclear Fission (cont.)

6. Section 24-3 Nuclear Fission (cont.) There must be sufficient mass to get the chain reaction started. If not the neutrons escape before striking other nuclei. Without sufficient mass, neutrons escape from the sample before starting a chain reaction. Samples with enough mass to sustain a chain reaction are said to have critical mass.critical mass Samples with mass that is much greater than the critical mass have a reaction that escalates at a violent level and can cause a nuclear explosion. This is the supercritical mass.

7. Section 24-3 Nuclear Fission (cont.) http://www.youtube.com/watch?v=qybUF nY7Y8w

8. Section 24-3 Nuclear Reactors Nuclear fission produces the energy generated by nuclear reactors. The fission within a reactor is started by a neutron-emitting source and is stopped by positioning the control rods to absorb virtually all of the neutrons produced in the reaction.

9. Section 24-3 Nuclear Reactors (cont.) The reactor core contains a reflector that reflects neutrons back into the core, where they react with fuel rods. Nuclear reactors produce highly radioactive nuclear waste. Breeder reactors produce more fuel than they consume.Breeder reactors

10. Section 24-3 Nuclear Reactors (cont.)

11. Section 24-3 Nuclear Fusion It is possible to bind together two or more lighter elements (mass number less than 60). The combining of atomic nuclei is called nuclear fusion. nuclear fusion Nuclear fusion is capable of releasing very large amounts of energy. The sun is powered by the fusion of hydrogen atoms to form helium atoms and a lot of energy.

12. Section 24-3 Nuclear Fusion (cont.) Fusion has several advantages over fission. −Lightweight isotopes are abundant. −Fusion products are not radioactive. −However, fusion requires extremely high energies to initiate and sustain a reaction.

13. Section 24-3 Nuclear Fusion (cont.) Fusion reactions are also known as thermonuclear reactions. thermonuclear reactions Many problems must be solved before nuclear fusion is a practical energy source.

14. A.A B.B C.C D.D Section 24-3 Section 24.3 Assessment Bombarding a nuclei with charged particle in order to create new elements is called ____. A.nuclear conversion B.nuclear decay C.induced decay D.induced transmutation

15. A.A B.B C.C D.D Section 24-3 Section 24.3 Assessment Thermonuclear reactions involve: A.splitting nuclei into smaller fragments B.fusing nuclei together to form larger particles C.bombarding nuclei with charged particles D.generating electricity in a nuclear reactor