I am not sure if I should be using this board or the nuclear board but I chose this board because it is for class work. Anyways over the past few months I have been collecting data from radioactive sources (Th-230, Am-241, Po-210, Pu-238). Now I understand that the number of events divided by the live time will be proportional to the strength of the source. What I am not clear about is what the FWHM of the peaks means. My professor had me take note of them and it seemed like the smaller the FWHM the better of a source it was; but I don't know what the FWHM is really a measure of (in terms of the quality of the source). Going along with that, why would two different Th-230 sources have a different FWHM for their primary peak?