I don't understand what this means??? Including artificially produced nuclides, more than 3300 nuclides are known (including ~3000 radionuclides), many of which (> ~2400) with decay half-lives shorter than 60 minutes. This list expands as new radionuclides with very short half-lives are characterized. What does a nuclide having a decay half-life shorter than 60 minutes mean exactly??? ( I understand half-lives kind of. From what I have learned, a half-life is the amount of time it takes for something to reduce to half it's value. I just don't understand how that would relate to the above question - What does a nuclide having a decay half-life shorter than 60 minutes mean exactly???