Hello people, I think the problem what I have is well known in experimental physics. Hope, somebody can helps me, thanks in advance. Here is: There is a source of neutrons with a flux of λ neutrons per minute, which you do not know and want to estimate. You open the detector for one minute and it counts N neutrons. The maximum likelihood estimator for λ would be N. Find the dispersion (or standard deviation) of this estimator. What will it be for the limiting case N=0? Looks like Poisson distribution, where λ isn't known.