ASTRON 1101 Lecture 3: Lecture 3
14 Feb 2017
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Document Summary
In europe before the 18th century, biblical chronology was the accepted method of finding the. Best method for finding the age of rocks: radiometric dating. They undergo radioactive decay, emitting particles to become a smaller, stable nucleus: ex. U-238 (92 protons + 146 neutrons = 238: u-238 decays to pb-206 (82 protons + 124 neutrons = 206) Decay of unstable nuclei is a random process. You can"t say when any particular nucleus is going to decay. You can only give the half-life the time it takes half the nuclei in a lump of material to decay. The half-life of u-238 is 4. 5 billion years: start with an ingot of solid u-238. After 4. 5 billion years, of the uranium has turned to lead. Newly formed zircon crystals are frequently contaminated with uranium, but never with lead. Zircon crystals are difficult to destroy, easy to detect. Grind up a zircon, do a chemical analysis, find the relative amounts of pb-206 and u-238.
