# Thread: modelling!

1. ## modelling!

A radio active element is know to decay at the rate of 2% every 20yrs. If initially you add 165g of the element, how much would you have in 60yrs.
what is the half life time of the element.

i formulated the model as

$\displaystyle E_{t+1} = 1.02E_{t} , where t \sim O(20)$

$\displaystyle E_{0} = 165g$

$\displaystyle t= 0$

solution

$\displaystyle E_{1} = 1.02E_{0}$

$\displaystyle t= 3$

$\displaystyle E_{4} = 1.02^4 E_{0} = 1.02^4 * 165 (in 60yrs)$

pls cross check to correct me and how do i compute the half life?

thanks

2. ## Re: modelling!

The half-life equation is exponential and continuous so a discrete model isn't going to work here. Read this.

Now, a 1/2 life is the time it takes for 50% of the material to decay. You know that 2% of your material decays in 20 years. So how much time would it take for 50% to go?

-Dan

3. ## Re: modelling!

In your answer where you have 1.02 it should be 1/1.02 and in the last line the index should be 3 not 4.
After n half lives the original mass