I've got a question regarding half-life. Half-life is the time taken when the mass or countrate emitted of a radioactive sample drops to half. But if say, if a sample of 400 particular radioactive nuclides which go through radioactive decay. Won't the count rate reach 0 eventually, after decaying into a more stable state? (assuming no background count). Because if we plot a normal half-life curve, it would be exponential and would never reach 0 at all. And if these particular nuclides emit gamma radiation, its mass wouldn't drop at all because the photons are massless, right? Thanks.