1. Unit C RADIOACTIVITY: NATURAL AND ARTIFICIALRADIOACTIVITY: NATURAL AND ARTIFICIAL (HANK 9:57 )

2. C.1 Half-Life: A Radioactive Clock  It is useful to know what the rate of decay of a radioisotope is to predict:  The time a radioisotope used for medical purposes will remain in the body.  the length of storage for hazardous materials.  Ages of ancient organisms/civilizations.

3. Carbon Dating  The use of radiocarbon for dating began some 50 years ago and was based on the detection of the decay of the isotope C-14 which is formed when cosmic rays react with nitrogen gas to form a radioactive carbon dioxide molecule.  There are one of these for every million million atoms of carbon 12.

4. Half-Lives  The rate of decay for radioisotopes is measured in half-lives.  A half-life is the amount of time it takes for one-half of a radioisotopic sample to decay into something else.  For instance, if H-3 has a half-life of 12.3 years, and you have a 100 gram sample of it, how many grams would be left in 36.9 years?

5. Variable half-lives  Half-lives can vary from a few seconds to a few billion years.  After 10 half-lives, only 1/10,000 th or 0.1% will remain.  If you are considering very large numbers of atoms, ie: 6.02 x 10 23, then even after 10 half-lives there is still a considerable amount of the substance left.

6. C.3 Benefits of Radioisotopes  Ionizing radiation given off by certain radioisotopes can be used in nuclear technology such as:  Tracer studies where the radiation is used to track cellular abnormalities, locate damaged areas and aid in therapy.  Irradiation, where the radiation is used as an energy source to treat medical conditions like tumors or leukemia and to sterilize medical equipment/seal plastic containers.

7. Tracers  Radioisotopes called tracers can be used to detect certain elements that are known to collect in specific places in the body.  Cesium-137 is used as an external source to treat shallow tumors.

8. Radiation Detectors  Devices called scintillation counters detect entering radiation as light emitted by the excited atoms when hit with the radiation.  Solid-state detectors monitor the movement of electrons through semiconductors like silicon. Liquid Scintillation Counters

9.  A cloud chamber is a glass filled with supersaturated water vapor. As radiation passes through the chamber, the vapor condenses on the ions formed leaving a white particulate trail.

10. Artificial Radioactivity  Also called transmutation, Rutherford was the first to create an element different from the original by bombarding helium with nitrogen to form oxygen and hydrogen.

11.  From 1940 to 1961 Glenn Seaborg and coworkers discovered 10 new element; numbers 94-103  None occur naturally. All were made by high- energy bombardments of heavy nuclei on various particles. Glenn Seaborg and John F Kennedy