The half life of the radioactive element Strontium-90 is 37 years. In 1950, 15 kilograms of this element released accidentally. How do you determine the formula which shows the mass remaining after t years?

1 Answer
Apr 4, 2017

#N(t) = 15Kgxx(1/2)^(t/color(red)37)#

Note: The half life of Strontium-90 is now published as 28.8 years. This will require adjustments of all the following values in #color(red)(red)#.

Explanation:

The formula for the half life of an exponentially decaying substance is:

#N(t)=(No)xx(1/2)^(t/(t1/2))#

#N(t)# ... is how much is still here.
#No# ... is how much we started with.
#t# ...... is the time we have measured since the start of the decay.
#t1/2# ... is the already calculated half life of the specific substance.

To calculate the mass of Strontium-90 remaining after #t# years, plug in the given values into the formula:

#N(t) = 15Kgxx(1/2)^(t/color(red)37)#

For example #color(red)37# years after 1950, the remainder of the #15Kg# of Strontium-90 released would be:

#N(67) = 15Kgxx(1/2)^color(red)(37/37) = 15Kgxx(1/2) = 7.5Kg#

In 2017 (now) the amount left is #15Kg xx (1/2)^color(red)1.8 = color(red)4.3Kg#