You can
put this solution on YOUR website!This same problem came up about a week ago, here is what I submitted then
:
The level of thorium in a sample decreases by a factor of one-half every 4.2 million years. A meteorite is discovered to have only 7.6% of its original thorium remaining. How old is the meteorite?
:
The decay formula: Ao*2^(-t/h) = A
Where:
Ao = initial amt
A = resulting amt
t = time (in millions of yrs)
h = half-life of the substance (in millions of years)
:
In this problem: let Ao = 1; A = .076
1*2^(-t/4.2) = .076
:
ln(2^(-t/4.2)) = ln(.076); find the nat log of both sides
:
.693 = -2.577; use the log equiv of exponents
:
= -2.577;
Multiply both sides by 4.2
-.693t = -2.577 * 4.2
:
-.693t = -10.823
t =
t = 15.6 million years old
;
:
Check solution on a calc enter 2^(-15.6/4.2) = .076..
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