Unit: Nuclear Chemistry Day 4 – Notes Unit: Nuclear Chemistry Fission, Fusion, and Applications of Nuclear Chemistry Pictures starting from upper right moving left: Radioactivity symbol, particle accelerator, mushroom cloud (nuclear explosion), Marie and Pierre Curie, cooling tower of nuclear power plant

After today you will be able to… Describe what happens in a nuclear chain reaction. Differentiate between fission and fusion reactions. Identify examples of how radioisotopes are used in everyday life.

Recall, during transmutations an atom can be converted into a different atom through radioactive decay or by bombarding a nucleus with particles. Today, we will focus on the latter by learning about fission and fusion.

Nuclear Fission Fission: occurs when a nucleus is split into smaller pieces. This process begins by colliding a nucleus with particles such as neutrons. The resulting nucleus is highly unstable and decays. This causes a chain reaction where particles emitted from the initial reaction bombard other nuclei, causing them to break apart.

Example: Uranium-235 n 1 U 235 92 The neutrons released from the decay of U-236 will collide with other U-235 atoms, repeating this process all over again (chain reaction). A neutron collides with the U-235 atom. U-236 is formed. Kr 91 36 U 236 92 n 1 ENERGY n 1 The U-236 atom is unstable and decays. n 1 Ba 142 56

Nuclear Fission Uranium-235 and Plutonium-239 are the only fissionable isotopes. These reactions release a large amount of energy.

Nuclear Fusion Fusion: occurs when nuclei combine (or fuse together) to produce a new nucleus of greater mass. Example: Production of energy from the sun 2 H 1 4 He 4 2 + e +1 + energy

Nuclear Fusion Releases far more energy than fission reactions. These reactions require very high temperatures in order to occur (~40,000,000°C).

Real-World Applications: C-14 Dating Scientists often find the age of an object that was once living by measuring the amount of carbon-14 it contains. Recall, C-14 has a half-life of 5730 years. This is its nuclear decay: https://c14.arch.ox.ac.uk/embed.php?File=ams.html C 14 6 N 14 7 + e -1

Real-World Applications: C-14 Dating All living things contain C-12 and C-14 in a fixed ratio. Once an organism dies, the ratio of C-14:C-12 changes, which allows archeologists to estimate its age. https://c14.arch.ox.ac.uk/embed.php?File=ams.html

Real-World Applications: C-14 Dating The most accurate way to examine the C-14 content is through use of a mass spectrometer. https://c14.arch.ox.ac.uk/embed.php?File=ams.html First, the carbon in the sample must be converted into graphite or carbon dioxide. This is can be done by burning a portion of the sample.

Real-World Applications: C-14 Dating The sample is then injected into a mass spectrometer and ionized. Due to the different masses of carbon having different angles of deflection, a scientist can count the individual C-14 atoms in the sample. https://c14.arch.ox.ac.uk/embed.php?File=ams.html

Mass Spectrometer: https://c14.arch.ox.ac.uk/embed.php?File=ams.html

Real-World Applications: U-238 But what if all of the C-14 in a sample has decayed or the sample is non-living? Similar to carbon-14, uranium-238 is used to date specimens. Uranium is naturally found in most rocks, seawater, and in Earth’s crust. It has a half-life of 4.5 billion years. U-238 is specifically used in dating rocks and fossils. https://c14.arch.ox.ac.uk/embed.php?File=ams.html

Real-World Applications: I-131 Radioisotopes can be used to diagnose medical problems or treat diseases. Specifically, iodine-131 is a radioisotope given to patients to check for abnormal thyroid function. Patients are given a drink containing the radioisotope (Na131I).

Real-World Applications: I-131 Since the thyroid extracts iodide ions from the bloodstream, the ions are absorbed and its radioactivity is used to create an image on a screen. From the image, doctors can examine the amount of iodine absorbed and determine if a person has hyperthyroidism or thyroiditis.

Real-World Applications: Co-60 The strong penetrating power of gamma rays allows it to be useful in the treatment of cancer. Cobalt-60, which is produced in particle accelerators, emits both beta and gamma radiation.

Real-World Applications: Co-60 The Co-60 is placed into a gun that is used to direct the radiation to where the tumor is located. The cells of the tumor are destroyed and it decreases in size. However, gamma radiation can also destroy healthy cells making those treated very ill.

Questions? Begin WS4