25.3 Fission and Fusion of Atomic Nuclei SWBAT describe what occurs during fission and fusion, and identify key terms associated with these processes

Nuclear Fission When the nuclei of certain isotopes are bombarded by neutrons they undergo fission. Fission: the splitting of a nucleus into smaller fragments. uranium-235 & plutonium 239 are the only fissionable isotopes In a chain reaction some neutrons produced react with other fissionable atoms, producing more neutrons, which react with still more fissionable atoms.

Fission of Uranium-235 Nuclear fission can release a lot of energy: 1kg of Uranium-235 can yield the same amount of energy generated by the explosion of 20,000 tons of dynamite What can happen with the released neutrons?

Nuclear Reactors Nuclear Reactors use controlled fission to produce useful energy. Most of the energy formed is heat. Heat is used to generate steam, which drives a turbine to generate electricity. Neutron moderation slows down neutrons so that the reactor fuel can continue the chain reaction. Examples of moderators include water and graphite. Neutron absorption traps slowed neutrons, decreasing the number of slow moving neutrons. Control rods made of cadmium are used to absorb neutrons. Neutron Moderation: Most neutrons move so quickly they could pass through a nucleus of a reactor fuel (U and Pu) without being absorbed Neutron Absorption: Control rods are very long and can extend to the reactor core (absorbing many neutrons) or pulled out (absorbing less-increasing reaction). If the reaction goes to quickly heat may be produced faster than the coolant can remove it, overheating the reactor core—leading to mechanical failure and the release of radioactive material (ultimately leading to the meltdown of the reactor core)

Nuclear Reactor Keep water under pressure so that it heats, but does not boil. Water from the reactor and steam generator that turn to steam are never mixed to contain radioactivity in the reactor area.

Nuclear Waste Fuel rods (made of U-235 or Pu-239) are a major source of nuclear waste. Spent fuel rods contain a mix of highly radioactive isotopes. Nuclear power plants place spent rods in holding tanks, where water cools the rods and acts as a radiation shield, reducing radiation levels. Fuel rods are considered spent when the fissonable isotope is reduced and can no longer ensure the output of the power station remains constant Spent fuel rods can be reprocessed however it is cheaper to mine new fuel than repurposing old fuel rods.

Nuclear Fusion Fusion occurs when nuclei combine to produce a nucleus of greater mass. The energy released from the sun is a result of nuclear fusion Fusion reactions release more energy than fission reactions! Fusion requires high temperatures to initiate the reaction and containing the reaction once it has started Deutirium + tritium  helium + neutron + energy currently being studied for potential nuclear energy

Check for Understanding What happens in a nuclear chain reaction? Why do neutrons in a reactor need to be slowed down? Why are spent fuel rods stored in water? How are fission and fusion reactions different/similar? Why is fusion not used to generate electrical power?

25.4 Radiation in Your Life SWBAT identify tools for detecting radiation and the use of radiation in the medical field.

Dating a Fossil Ages of artifacts and fossils can be determined by carbon-14 dating. Carbon-14 is an isotope of Carbon containing 6-protons & 8-neutrons. Carbon-14 has a half-life of 5730 years (decays to N-14) A wooden tool was found to have 50% of Carbon-14 content found in living wood. How old is the wooden tool?

Detecting & Using Radiation Devices used to detect radiation include: Geiger counters, scintillation counters, and film badges. These devices detect emitted ions or show photographic evidence of radiation. Neutron activation analysis is a procedure used to detect trace amounts of elements in samples. Radioisotopes have an unstable nucleus and undergo radioactive decay. The production of certain radioisotopes can help identify elements originally in the sample. Radioisotopes can be used to diagnose & treat medical problems Geiger counter: gas filled metal tube with electrode that becomes ionized when radiation penetrates producing a clicking sound https://www.youtube.com/watch?v=upPiJ9vOYiY Thyroid problems can be diagnosed using I-131. Thyroid extracts iodide from the bloodstream and uses it to make hormones, a few hours after intake of radioisotope I-131, the uptake by the thyroid is measured. This process is similar when detecting brain tumors and liver disorders, Phosphorous-32 is used to detect skin cancer. Radiation-treatment of cancer gamma rays can be used to damage or kill tumor cells