posted by Nancy .
I have: the half life of U-238 is 4.5 x 10^9 yr. A sample of rock of mass 1.6g produces 29 disintegrations per second. find percent by mass of U-238 in rock.
I have 4.5x 10^9x60x60x365x24=1.419x 10^17=
.693/1.419 x10^17 =4.883x10^-18 =rate
1.6/238=.006722 x 6.022 x10^23=4.048 x10^21
then 4.048x10^21 x 4.883 x 10^18=19766 disintegrations per second
29/19766 =.001467 x 100 =.146
is this correct?
yes it it. 0.15%