Half Life question?

When you are doing radiometric dating, you are comparing the amount of the parent isotope to the amount of the daughter isotope. For best results, this ration should be about 1:1. That is, you want the half life to be as close as possible to the date that you are seeking. The problem with uranium-lead dating is that the long half life means that there will be very few daughter atoms after only a million years compared to the those of original parent isotope. The accuracy of the dating goes down when the ratio of these two moves away from this ratio.