How do I determine the age of a sample using radiocarbon dating?

[mss90]

Homework Statement

9.2g of carbon got an activity of 1.6Bq, how old is it?

Homework Equations

A = -(lambda)*N
N=No * e ^ -(lambda)*t
(lambda) = ln2/t1/2

The Attempt at a Solution

The question doesn't specify which isotope of carbon it is so halflife remains unknown.
I can't see how to solve this by only knowing the mass and activity.
Could anyone give me pointers?

R

 

[andrevdh]

They are most likely referring to carbon-14 dating.

 

[mss90]

Alright in that case we know the half life and can find the decay constant.
Using A = -(lambda)*N we can find N as well (not sure If I need to divide the activity on 9.2g to get it per grams?)
However It still leaves No and t unsolved.

An alternative method is to; N=No * e ^ -(lambda)*t |*(lambda) => A=Ao * e ^ -(lambda)*t
But it seems to get me to the same "deadend" where Ao and t is unsolved.
I thought I might be able to set t=0 to get Ao but that only makes the expression " e ^ -(lambda)*t" equal 1.
Any tips?

R

PS: thanks for fast reply

 

[andrevdh]

Atoms per mole.
The sample starts out with a certain fraction of it being carbon-14.
Over time the amount of carbon-14 decays.