What fraction of a given sample of a radioactive nuclide remains after four half-lives?

1. What fraction of a given sample of a radioactive nuclide remains after four half-lives? • What are the different types of common radioactive decay?

2. Solution: 1/16 the original amount. Each half-life is the time it takes for 1/2 for the substance to decay. So four half-lives would be ½ * ½ * ½ * ½ = 1/16 • Alpha emission, beta emission, gamma emission, positron emission and electron capture

4. Radiation Exposure • Nuclear radiation can transfer the energy form nuclear decay to the electrons of atoms or molecules and cause ionization (freeing of electrons) • This is harmful. Long term exposure to radiation can cause DNA mutations which results in cancer • People at higher altitudes receive higher exposure levels because of increased cosmic ray levels at high altitudes.

5. Radiation Exposure • What are some other sources of Radiation that we come into contact with?

6. Radiation Exposure • Radon-222 is a radioactive particle that gets trapped inside of homes, it is released by certain rocks and seeps into holes in house foundations. Radon trapped in homes increases the risk of lung cancer, especially in smokers. How do we detect it? What have you seen? What have we learned about radiation?

7. Radiation Detection • Film badges- Becquerel’s experiment showed radiation exposes film. Film badges are used to show the approximate amount of radiation exposed to someone working in it. • Geiger-Muller counters • Scintillation counters

8. Applications of Nuclear Radiation • Radioactive Dating- process which the approximate age of an object is determined based on the amount of certain radioactive nuclides present. Ex. Carbon-14 • Nuclides with longer half-lives have been used to date minerals and lunar rocks more than 4 billion years old. Ex. Geologists use a potassium isotope for dating: (40K → 40Ar +1 β) What kind of Radioactive decay is taking place?

9. Applications of Nuclear Radiation • Radio Active Nuclides in Medicine- Cobalt-60, Radioactive tracers are radioactive atoms that are incorporated into substances to trace movement of the substances with radiation detectors in order to test and diagnose for cancer and other diseases. • In Agriculture- Used in fertilizers. The amount of a radioactive tracer found in the plant indicates how affective the fertilizer uptake is. Prolonging the shelf life of food- substances like cobalt-60 are used to kill bugs and bacteria that spoil and infest food.

10. Nuclear Waste • Fission- A large atom with a large nucleus breaks apart and releases particles and energy. Process that powers nuclear power plants. Lots of nuclear waste, relatively cheap and easy to do. • Fusion- two or more small atom nuclei combine to form a larger nucleus. This is the reaction that powers the sun, not as much nuclear waste. It is impossible to contain right now.

11. Containment & Storage The radioactive waste from fission that we currently create in reactors has a really long half-life, hundreds of thousands of years. There need to be facilities that can contain the waste so that the public is shielded from its harmful effects. Currently, most of the waste is disposed of on-site in pools then moved to dry storage casks for containment. Neither one of these are meant for long term storage.

12. Disposal of nuclear waste • Disposal is done with the idea of never retrieving the materials. Because of this, careful planning must be done in order to contain the huge amount of waste that are currently around the United States. • Yucca Mountain

13. Sources • http://radyananda.wordpress.com/2011/03/26/us-stores-spent-nuclear-fuel-rods-at-4-times-pool-capacity/ • http://www.arpansa.gov.au/radiationprotection/basics/other.cfm • http://www.avweb.com/news/aeromed/181873-1.html