The first day I "joined" phys-l a member posted a question about the stat. distrib. of G-M detected events. I replied Poisson .......
Off l. he gave me data to calc. the dead time, which was (is) v. ~ one milisec. This is highly unusual, being typically 0.1ms. So I repeated and sure enuf 1 ms. This was done w/ very low counting rates. (10 -- 20 CPS instead of the usual 200 cps) A high rate is typical in order to quickly obtain "good" stats and ignore background. I then measured the dead time for various rates w/a number of tubes. The reason for the variation is intuitively obvious and confirmation may be found (I think.) by comparing w/various diameter tubes.
Next is, so what? If one makes dead time corrections at high rates no error, but if one uses the correction found at high rates for low rates the correction found is insignificant, but incorrect! For example the correction using 0.1ms at 200 CPS is ~ 2% and at 20 ~ 0.2%. But the low rate is ~ 1ms and the correction, therefore, also 2%.