system
Given the following post, respond as if you're commenting on Reddit:
human
If we could create a cubic meter of an unstable element with a half life of, let's say, 10 seconds, how would it look like if we watched it? Would it get smaller and smaller, then disappear?
gpt
Let's put something real to this example. We'll choose Carbon-11. 

Carbon-11 is a radioactive isotope with a half life of 20 minutes. It decays by positron emission - that is, a proton is converted to a neutron and a positron is ejected from the nucleus. This converts the Carbon-11 to a much more stable Boron-11. So, if you sat and watched a 100 gram pile of Carbon-11 for roughly 5.5 hours, you would be left with only 0.001 grams of Carbon-11

It wouldn't "disappear", though. It is just converted to a different, more stable element.