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If a radioactive substance has a half-life of 4,500 years, how much of an initial mass of 100g will be left after 20,000 years? And what is the constant of decay of this substance? Thank you for help.

 Sep 10, 2018
 #1
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deleted.

 Sep 10, 2018
edited by Guest  Sep 10, 2018
edited by Guest  Sep 10, 2018
edited by Guest  Sep 10, 2018
 #2
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A = A(0) * 1/2^(20,000/4,500)

A = 100 * 1/2 ^4.44.....

A =100 x 4.59....

A =~4.59g remaining after 20,000 years.

 

k = -(ln2) / half-life

k =- (0.693147) / 4,500

k = -0.000154 - which is the constant of decay.

Check: A =100 x e^-(0.000154*20,000)

             A =100 x e^ -3.08

             A =100 x 0.0459.....

             A =4.59 grams.

 Sep 10, 2018

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