The half-lives of C-14 is 5730 years. A sample that has decayed for three half-l
ID: 233398 • Letter: T
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The half-lives of C-14 is 5730 years. A sample that has decayed for three half-lifes is 3 times 5730 years or 17,190 years old. To determine how much C-14 is in a sample, radiation detectors count the number of BETA particles released by radioactive decay. The result is called the ACTIVITY (disintigrations per minute per gram of carbon-dpm/g). Modern samples have an activity of about 12.5 dpm.g. Older sample have values less than the modern value. C-14 measurements are often expressed as " percentage modern", which is the ratio of sample activity to modern activity. For example, a percentage modern value of 25 percentage means that the sample contains 25 percentage of its initial C-14. The sample size required for this method depends on the type of material, but is generally in the tens to hundreds of grams range. Very small samples just don't have enough C-14 to be reliably measured. The smallest C-14 activity measurable with most methods is about 0.2 percentage modern, which corresponds to about 9 half-lives. About what percent of modern C-14 remains in a sample that is two half-lives old? 2 percentage 12 percentage 3 percentage 10 percentage 25 percentage What percent of modern C-14 remains in a sample that is five half-lives old? 2 percentage 3 percentage 5 percentage 25 percentage 50 percentage What is the approximate age, in years, of a sample that contains 90 percentage of its original C-14 900 1950 3000 5000 27500 What is the approximate age, in years, of a sample that contains 30 percentage of its original C-14? 4500 6200 7303 9700 15500 What is the approximate age, in years, of a sample that contains 3 percentage of its original C-14? 850 1750 3000 5000 28000Explanation / Answer
11. 25%.
12. 3%.
13. 900 years.
14. 9700 years.
15. 57,300 years.
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