Radioactive Isotopic Decay

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The graph is interactive and meant for you to use. It illustrates how the amount of a radioactive parent isotope decreases with time. This amount is a percentage of the original parent amount. Time is expressed in half-lives. Experiment by dragging on the graph. For example when 42% of the parent still remains, 1.23 Half-Lives of time has passed. Answer the questions on the right. Click the next button when you are ready to continue.

1. Approximately what percentage of parent isotopes remains after 0.5 half-lifes have passed? 50.0% 70.7% 0% 100% 25.0% 2. How many half-lifes must pass before only 10.2% of the original parent isotopes remain? 1.0 Half-life 1.5 Half-life 2.5 Half-life 3.3 Half-life 3.5 Half-life 3. Assume a parent isotope has a half-life of 100 million years, how old is a sample that contains 15.4% of its original parent isotopes? 100 Million Yrs 200 Million Yrs 250 Million Yrs 270 Million Yrs 300 Million Yrs 4. Assuming a parent isotope with a half-life = 4.5 billion years, what percentage of the original parents remains after 6.75 billion years have passed? 50.0% 35.4% 25.0% 15.5% 10.3%