Decay correction of samples

You may have posted this information somewhere, but there are so many forums we couldn't find it...

Could you tell us how you did the decay correction for your air filter measurements? Were the measured nuclides decay corrected to, for example, the mid-point time over which the particular sample was taken? Quite important to be clear about this for the short-lived nuclides.

Jim Smith and Kittisak Chaisan, England