1.12% of a certain radioisotope decay in 5.2 years, what is the half-life of this isotope? 2. Charcoal found under a stone at Stonehenge, England,

1.12% of a certain radioisotope decay in 5.2 years, what is the half-life of this isotope? 2. Charcoal found under a stone at Stonehenge, England, has a carbon-14 activity that is 0.60 that of new wood. How old is the charcoal? (The half-life of carbon-14 is 5,730 years.) 3. The radioisotope potassium-40 decays to argon-40 by positron emission with a half-life of 1.3 × 10 9 yr. A sample of moon rock was found to contain 78 argon-40 atoms for every 22 potassium-40 atoms. The age of the rock is 4. The isotope of iodine with mass number 128 undergoes beta decay with a half-life of 25.00 minutes. How long will it take for 93.75% of a sample of pure 128 I to decay? 5. Petroleum is a fossil fuel containing many different carbon compounds. If the carbon atoms in petroleum have been in the ground for 100 million years, what fraction of the initial 14 C atoms is still there? (t 1/2 = 5,370 yr)

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