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Need help answering this question...........

The half-life of radium-226 is 1620 years. If a sample of material contains 16 milligrams of radium-226, how much will it contain in 1620 years? How much will it contain in 3240 years? How long will it take for the sample to contain 1 milligram of radium-226?

Hey Buddy, here is how you approach and answer this problem:

- After 1620 (its half-life) half of the radium-226 would be left so:

16mg/2=8mg.
 
- After 3240 (two half-lives) half of a half would be left or:

16mg/2=8mg and then 8mg/2=4mg.

- half-life is 1620 years and so it would take 4 half-lives to get the sample down to 1mg or 4x1620=6480:
 
After 1 half-life (1620 years)–16mg/2=8mg
After 2 half-lives (3240 years)–8mg/2=4mg
After 3 half-lives (4860 years)–4mg/2=2mg
After 4 half-lives (6480 years)–2mg/2=1mg

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