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Lab 6 |
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| Procedural Tips
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Print a copy of the Check-list for this lab. Initial each item on the Check-list as completed. Why do I need to wear safety goggles? Some amount of radiation is always present. This radiation is known as background radiation. We will use a Geiger-Mueller detection tube to determine background radiation and determine the counts per minute given off by some radioactive substances found in our everyday life. Various shielding materials will be used to determine the affect of the type of material and distance from the radioactive source on the radiation detected by the Geiger-Mueller detection tube. Concept of half-life will be demonstrated with M&M candies. A graph of activity versus time will be prepared.
Most elements have isotopes. Isotopes are atoms of the same element, but with different atomic masses. Isotopes have the same number of protons, but differing numbers of neutrons. Some isotopes are unstable or radioactive. Radioactive isotopes decay by emitting energy from the nucleus. This process is called nuclear decay. There are three forms of energy associated with nuclear decay; alpha, beta and gamma radiation. Geiger-Mueller detection tubes are instruments that can detect and measure radioactivity. With a Geiger-Mueller detection tube you can check materials and environment for radioactivity. In order to avoid cellular damage, it is important for people dealing with radioactive materials or other sources of radiation to be shielded from the radiation. Shielding provides protection by blocking radiation. The type of shielding required is dependent upon the type of radiation exposure. Alpha particles are very heavy and do not travel far. A piece of paper is protection against alpha particles. On the other hand, gamma radiation consists of very high energy rays. Only very thick and dense shielding, such as lead or thick concrete, is adequate protection against gamma radiation. Another factor that influences the amount of radiation that the body receives is the distance from the radioactive source. The greater the distance, the lower the intensity of radiation received. All radioactive elements disintegrate according to their specific half life. The half life of a radioactive substance is the time required for half of the initial number of nuclei to disintegrate. Each radioactive isotope has it's own half life. Half lives can be as short as milliseconds or as long as millions of years. Read pages 51-53 in your laboratory manual before coming to lab. Answer the pre-lab questions on page 55. You are also encouraged to do Q.4, Q. 5, Q.6 and Q.7 on pages 57-58 before coming to lab. The following problems are found in your Timberlake textbook on page 109 and are due at the beginning of the lab session. Note: you must use the unit-factor method where applicable, include units with your calculations, and show all of your work in order to obtain the maximum number of points.
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