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.