Yesterday I was adding some "related investigations" to the required practical pages when I realised that I hadn't included details of a computer simulation to be used for radioactive decay. I like student to build their simulations themselves as it gives them more understanding of the underlying physics so I set about making one in Excel. Plotting decay curve is simple enough but really doesn't get across the idea that this is something to do with random decay so I though of ways that I could use the random number generator in Excel to decide whether a nucleus lives or dies.

I set the random function to generate numbers from 1 - 10 in 100 cells. I then used an IF function to put a 0 in a second cell if the value was <4 and a 1 if not. I repeated this 12 times to get a grid of 1's and 0's. I used these 1's and 0's to kill off nuclei by multiplying them together, as soon as a 0 appeared the row became 0 indicating a decayed nucleus. A bit difficult to explain but the details are here.

The nice thing about this simulation is that you can control the probability of decay and see the effect on the half life and decay constant. This is easy if the probability of a decay per second is 1/2 since the half life will be 1 second and the decay constant ln(2), but for any other examples its more complicated but the equation seems to do the trick. Would make an excellent investigation.