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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- 3 H- half life of 12.3 years 238 U has a half life of 3.8 billion years

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## Chapter 4

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**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

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