Chapter 5: Star POWer

My Notes: Fusion pages 223-225 Fusion reactions fuel stars. The carbon on Earth comes from those fusion reactions in the stars. Centers of stars can be 10 million degrees Celsius. A candle, by comparison, is about 400 degrees Celsius. Four Hydrogen fuse to make one helium. Two of the protons from the hydrogen atoms join with 2 electrons and become 2 neutrons. So, ONLY 1 helium atoms are formed and the additional neutrinos are emitted along with a lot of energy! Some mass is converted into energy. For example, 454 g of hydrogen fuses to make only 451 g of helium. The “lost” 3 grams (1%) is converted into energy… like heat and light from the sun. Continued, next slide…

My Notes: Fusion pages 223-225 The strong force holds protons and neutrons together. 8) The electrostatic force is the force between electrons and protons. It is not as powerful as the Strong force. Scientists know it is weaker because the electrostatic force is responsible for chemical reactions, which require less energy than nuclear reactions (influenced by the strong force).

My Notes: Radioactive Decay pages 225 - 227 Fusion is not the only way nature alters a nucleus. Some nuclei break apart on their own. This is called radioactive decay. An alpha particle is a helium nucleus, with 2 protons and 2 neutrons. Charge is conserved, and mass numbers are the same. Beta and gamma particles are also types of radioactive decay particles. All radioactive decay processes are random… you cannot tell exactly which particle will decay at any given moment. But you can tell the RATE of decay of a group of particles. Continued on next slide…

My Notes: Radioactive Decay pages 225 - 227 The half-life is unique to each type of particle. It tells us how much radioactive material will be present at a given time. For instance, it 100 g sample of Iodine-131 has a half-life of 8 days, then after 8 day there will be 50 grams left. Half-lives vary from 4.5 billion years for Uranium-238 to just fractions of a second for some elements such as most isotopes of gold, and all those “fake” elements created in research facilities. (Sorry. That last sentence was my soapbox comment because I think they shouldn’t be counted as real elements…)

My Notes: Fission pages 228 - 229 Fusion involves putting nuclei together. Fission involves taking nuclei apart. Both involve changing the nuclei. In fission, nuclei split into approximately equal parts. Nuclear power plants use fission reactions to produce energy. Sample reaction: Notice that the mass numbers (top boxes) equal the same numbers on the left as on the right side. The mass is conserved. Notice that the atomic numbers also balance in fission reactions. Continued on next slide…

My Notes: Fission pages 228 - 229 Chain reactions in power plants occur when a reactant collides with another particle, causing a 2nd fission, etc. The minimum amount of material needed to produce an atomic explosion is called the critical mass. For some bombs, it only takes about 45 lbs of material to set off an atomic bomb. Controlled fission does not explode. Water coolants surrounding the material also absorb some of the extra neutrons. Energy from the fission is used to boil water, which turns turbines and produce electricity. Some of the products are radioactive isotopes with very long half-lives; they last a long time. They are difficult to dispose of safely. We currently bury them in containers.