Chapter 4 Chad Stessman. Half-life Radioactivity is a random process Half life is time it take half...
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Transcript of Chapter 4 Chad Stessman. Half-life Radioactivity is a random process Half life is time it take half...
Chapter 4
Chad Stessman
Half-life
• Radioactivity is a random process
• Half life is time it take half of the atoms of a sample to decay
Half-lives
• Tritium-3H- half life of 12.3 years
• 238U has a half life of 3.8 billion years
• Amount remaining after a certain number of half-lives is 1/2n. Where n= number of half lives
Radioisotope dating
• Radioactive decay can be used to determine the age of a sample.
Carbon-14 dating
• 14C is an isotope of carbon.
• Formed by bombardment of nitrogen in the atmosphere with cosmic rays, neutrons
• 14C incorporates into living creatures through the carbon cycle.
• 14C incorporates into living creatures through the carbon cycle
• When plant or animal dies, it is no longer incorporating 14C
• 14C half life is 5730 years
• After about 10 half-lives or 50,000 years too little 14C to be effective.
• 14C formation not always constant, need to find references
Tritium Dating
• 3H has a half-life of 12.3 years
• Used to determine age of brandy and wine samples 10-100 years old
Other isotopes used in dating
• Potassium-40 1.3x109 years
• Rhenium-187 4.3x1010 years
• Uranium-238 4.5x109 years
Artificial Transmutation
• Middle ages alchemists tried to accomplish transmutation
• Nuclear reactions can change atoms
Uses of Radioisotopes
• Around 3000 radioactive isotopes can be produced from stable isotopes.
Tracers
• Used in physical, chemical or biological systems.
• Used to look for leaks, follow reactions, get images of biological processes.
Nuclear Medicine
• Radiation Therapy
• Diagnostic Uses
Radiation Therapy
• Use radiation to destroy rapidly growing cancer cells.
• Aim radiation at cancer cells
Diagnostic Uses of Radiation
• Radioisotopes are use to image or diagnose problems with the body functioning.
• Technium-99m-gives up a gamma ray to become more stable
99mTc 99Tc + gamma
• Used in gamma imaging of heart.