Radio-Active Dating HALF LIFE Recap of Atoms Parts of an atom Nucleus (middle of atom) PROTONS – positive charge NEUTRONS – no charge ELECTRONS (outside nucleus) Negative charge Mass Number & Isotopes Protons & Neutrons have a mass of 1 each Mass number = protons + neutrons Some elements have atoms that have a different number of neutrons ISOTOPES This changes their mass Radio-active Decay Isotopes that have unstable nuceli undergo radio-active decay Radioactive isotopes This means they release particles or radiant energy or BOTH Half-Life TIME it takes for ½ the amount of a radioactive isotope to decay Many half-lives are known and can be seconds to thousands of years Carbon Isotopes Our body has lots of carbon in it Mostly Carbon-12 Some Carbon-14 Carbon-14 has a half-life of 5,715 years Try it out If our sample starts with 100 sample size of carbon-14 and it now has 25, how many half lives have gone by? How many years old is the sample? 2 half lives 11,430 years
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