Posted by **Mindy** on Friday, November 11, 2011 at 6:47pm.

The half-life for beta decay of strontium-90 is 28.8 years. A milk sample is found to contain 10.3 ppm strontium-90. How many years would pass before the strontium-90 concentration would drop to 1.0 ppm?

- Chemistry -
**DrBob222**, Friday, November 11, 2011 at 8:02pm
k = 0.693/t_{1/2}

Substitute k into the equation below.

ln(No/N) = kt

No = 10.3 ppm

N = 1.0 ppm

k from above.

t = ?

- Chemistry -
**Mindy**, Friday, November 11, 2011 at 8:57pm
DR.BOB222 ENGLISH PLEASE?????? I know how to get the beta decay for strontium. just having a hard time with the concentration of strontium and the amount of yrs. passed....please help!!

- Chemistry -
**DrBob222**, Friday, November 11, 2011 at 9:42pm
All you need to do is to substitute 28.8 years into equation 1 I gave you to solve for k, then substitute k into the

ln(No/N) = kt and solve for t.

I TOLD you what to substitute for No and I told you what to substitute for N and k. You have only to solve for t. t is approximately 100 years for the Sr to decay to about 1.0 ppm.

- Chemistry -
**joe**, Monday, October 8, 2012 at 8:52pm
the half-life of cobalt-60 is 5.20 years.. how many milligrams of a 2.000-mg sample remains after 6.55 years?

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