I don't see any reasons why you could not cool radioactive isotopes to essentially zero Kelvin and observe the decay rate. It would probably be hard(er) to do w

I don't see any reasons why you could not cool radioactive isotopes to essentially zero Kelvin and observe the decay rate. It would probably be hard(er) to do with larger chunks because the decaying nuclei would dump parts of their energy into the sample but if you only use a single atom or maybe tens or hundreds of them and measure the time until the first decay event or between the fist two events you could certainly determine the decay rate close to absolute zero.