Posted by **devin** on Monday, December 5, 2011 at 7:38pm.

If the radiicativr decay of nuclear explosion contains 90 Sr , with a half life of 28.1 years how long will it take for 99 of this radioaioot to decay

- chemistry -
**DrBob222**, Monday, December 5, 2011 at 7:50pm
99 what? 99 grams? 99 tons? 99%. I suspect 99%.

Two steps. First determine k.

k = 0.693/t_{1/2} and substitute into the following:

ln(No/N) = kt

I would set No = 100 if that is 99%.

Then N = 1% (if 99% is gone)

k from above

Solve for t in years.

- chemistry -
**devin**, Monday, December 5, 2011 at 8:01pm
Sorry don't understand it is 99 percent

- chemistry -
**devin**, Monday, December 5, 2011 at 8:09pm
Ln(100)/1)=(0.693/t^1/2)(t). ??? Don't get it

- chemistry -
**DrBob222**, Monday, December 5, 2011 at 10:58pm
There isn't anything to get. Can you punch the calculator? That's all there is to it. Do it in steps. Don't try to muddle it up by putting all of it together.

ln 100/1 = 4.605

0.693/28.1 = 0.02466 = k

so

ln(100/1) = 0.02466*t

4.605 = 0.02466t

and t = 4.605/0.02466 = ? or about 200 years more or less.

## Answer this Question

## Related Questions

- chemistry - How long will it take for 25% of the C-14 atoms in a sample of C-14 ...
- chemistry - The isotype caesium -137, which has a half life of 30 years, is a ...
- Physic - A radioactive element x has half life of 30 days and will decay to ...
- Physic - A radioactive element x has half life of 30 days and will decay to ...
- Physic - A radioactive element x has half life of 30 days and will decay to ...
- DrBob222 - On Monday you helped me to understand and answer the one question, ...
- chemistry - With a half-life of 14.3 years, how long will it take for100 g of ...
- physics - A building has become accidentally contaminated with radioactivity. ...
- chemistry - If there are 80 milligrams of a radioactive element decays to 10 ...
- math - 39mg radioactive with 1/2 life is decay total in 2.5 years. How many mg ...