Radioactive Carbon Decay: Determining Age of Animal Remains

[dansics]

This is the question which I'm working on:
When an animal dies the radioctive carbon content of its body has an activity of 12 counts per gram per minute. Some animal remains are found to have an activity of 3 counts per gram per minute. If the half life of radioactive carbon id 5000 years,how old are the animal remains.

My solution:
Decay rate reduced from 12counts/gram/min to 3counts/gram/min. Therefore it must have passed 2 half-lives. So two half-lives must be 5000 x 2 = 10 000.
Is my method right?

 

[Vagrant]

Yes, your method is right.

It can also be written as R=R_{0} e^{-\lambda t}

where the total decay rate R of a sample of one or more radionucclides is called the activity of that sample.

 

[mgb_phys]

Yes you are correct.
The formula is a little more complicated if the animal didn't have the consideration to die a whole number of half-lifes ago!