What factors affect the rate of decay of a radioactive atom?

Question

I saw a specific quote that made me question this : "Other atoms in the universe don't influence the rate, it's just an intrinsic property of each separate atom that it has some chance to decay." (from this Q&A)

I'm assuming there are some factors that do influence rate of decay? Also assuming that statement is generally correct in a broad sense, or even technically correct because it only mentions other atoms not influencing the rate - I've no idea, why I'm asking.

But there has to be some factors that influence rate of decay, even if only at a quantum level, right?

I've read here amongst other answers. I understand this may not be answerable, or the answer is simply "best evidence says its random" - but that question is 3 years old, and I'm hoping maybe the consensus has changed/shifted/new concepts are being explored.

I'm also curious about environmental factors. i.e. could uranium 233 decay differently (more rapidly/slowly), on average, in different settings? What causes the differences (pressure, presence of other atoms, ?) - this part I've yet to find any answer on, the others, I assume, imply a standard environment to show randomness of decay.

To go further, and my apologies if my ignorance is showing, does the presence of one versus many atoms change the rate of decay (again, avg)

To restate the question (title): What factors affect the rate of decay of an atom?

Please comment with any improvements

Answer 1

There is one factor that definitely influences decay rates: speed. An accelerated radioactive nucleus will decay slower due to relativistic effects. An extreme example of this are cosmic ray-generated muons. A muon at rest decays to an electron, a neutrino, and an anti-neutrino after 2.2 microseconds on average. This would mean that, if it was traveling very close to the speed of light, it could only go about 660 meters before decaying. But, muons generated by cosmic rays high in the atmosphere are detectable on the ground dozens of kilometers below where they are created. This is because the muons are traveling at high speed and so decay at a slower rate due to time dilation.

Other effects require some interpretation. A critical mass of radioactive substance, such as in a nuclear fission bomb, can result in not just a speeding up of decay, but in an exponential explosion of decay. In a fission bomb, the neutrons released from one radioactive decay trigger the decay of multiple neighboring atoms. In one sense, the surrounding atoms speed up the decay of a given atom. In another sense, the neutrons bouncing around transmute the original isotopes into more radioactive isotopes. If a bomb uses uranium-235, you could say that the decay rate has not changed; the neutrons in the environment changed the $^{235}U$ to an excited $^{236}U$, which is much more unstable. So, everything decays at its natural rate.

There is an ongoing controversy regarding decay rates. Some labs that measure the rates of radioactive decay claim to see annual variations of about 0.1%. I call this controversial because some labs see the variation, some don't. The labs that do see variation posit that the changes are related to the Earth's distance from the Sun so that the local density of neutrinos or other particles are the cause of the variation. Those that are skeptical of the observation say that the labs have unaccounted for errors in their measurements. Here's a bibliography from December 2020 of hundreds of papers on the topic, both for and against. Again, the claim of decay rate variation is very controversial and most physicists are skeptical.