Question 1118991
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The fact that half-life is 1599 years means that


M(t) = M*2^(-t/1599)),     (1)


where  M  is the initial mass of the isotope, M(t) is its current mass at the current time moment t.


Indeed, at t = 1599 years you have from the formula (1) 


M(1599) = {{{(1/2)*M}}}.


Then at t = 1000 years the remaining mass of the initial 10 grams is


M(1000) = 10*2^(-1000/1599) = {{{10*2^(-0.6254)}}} = 10*0.6482 = 6.482 grams.


<U>Answer</U>.  6.482 grams of the isotope after 1000 years.
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