Right. If you know you have 500 trillion atoms in your sample and it shows 190 decays per day, then you can calculate that the half life is 5 billion years, for example. This is the first method I described in post 14. Sure. Atoms are tiny - which means you have many of them. A single microgram of uranium 235 has 2.5 quadrillion atoms and will have 7000 decays per day. You can easily get enough statistics from such a small sample, and we can prepare much larger samples. That has no influence on the half life.