I hope I put this in the right place.

I'm no mathematician or nuclear engineer, so please bare with me. Am I calculating this right?

Let's say, for example, a radiation monitor has an average background of 1872 CPS. During a scan the maximum count is say 2143 CPS. How much of a sigma increase is that?

Is this correct? :

Delta = MaxScan - AverageBkg = 2143-1872 = 271

Sigma = Delta/SQRT(AverageBkg) = 271/SQRT(1872) = 6.263 sigma increase

Searching the internet for a confirmation of this calculation gets over my head rather quickly. If the above calculation is wrong, could someone please tell me what the proper process is without getting all long haired about it?

Thanks much!