How do we know the rate of decay for radiometric dating is constant? http://www.purdue.edu/newsroom/research/2010/100830FischbachJenkinsDec.html
The link above talks about a paper by Sturrock et al. in which slight fluctuations were detected in radioactive isotope decay rates and  might affect how we uses radiometric dating. Young Earth creationists did used this to claim that radiometric dating is not accurate and that it is base on assumptions. https://www.discovercreation.org/blog/2012/10/26/80-years-of-scientific-fact-wrong-radioactive-decay-rates-not-constant/ Could the rate of radioactive decay be different in the past that today?
 A: It’s important to consider the possible size of effects in cases like this. 
If there were variations in decay rates of parts per thousand (see link in Question), there might be similar errors in radio-dating results. The 4 billion year age of Earth might be off by millions of years!  That’s far from a big enough effect to support a young-Earth position. 
In general, it’s a mistake to seize in just the existence of some effect without considering the magnitude of that effect and how that compares to observation. Parts per thousand, parts per million effects can be scientifically interesting complexities, but they don’t really change the original observations. 
On the question of how we know about past, there are (at least) two lines of argument. 
There’s a lot of experimental and theoretical knowledge about the process of decay. That supports the idea that it’s stationary: every second, an atom has the same chance of decaying. That leads (with small corrections) to constant rates, half-life behavior, etc. 
But could the past be Really Different? Here we rely on consistency of data: We know a lot about the past and it’s all consistent with constant rates. Somebody proposing inconstant rates would have to explain, in detail and with numbers, how that’s consistent with what we know about heat in the Earth’s core, consistent radio-daring of meteoroids and lunar material with multiple isotopes, matches between ice cores and ocean sediments, K-T layer daring, etc. It’s not sufficient to argue “it could be those can be explained” by a changing-rate Earth; one would have to actually show that explanation, in detail. That’s how the experimental method tests hypotheses. 
A: First of all, you shouldn't take creationists seriously; like flat earthists their views are totally out of touch with reality. Rates of decay have been tested many times in the laboratory and found to be near enough constant. However, in a few cases examples have been found where a change in temperature or a chemical compound involving the radioactive element has produced a very small change in the decay rate, but this is not a source of error in radiometric dating. If pin point accuracy is what you are looking for, you won't get it with radiometric dating, but if you are satisfied with results which are within a few percent of the truth, then that is usually achievable.
The error comes not from variable rates of decay, but from the very minute quantities that archaeologists, geologists and palaeontologists have to work with. In potassium argon dating, for example, only a tiny proportion of the volcanic tuff to be tested is potassium 40, and only 11 percent of that becomes Ar40, so the lab has to detect and measure the minute traces of argon which radioactive decay has produced in the sample.
In some cases, several different dating methods are used to establish the age of some rock or artefact, and if they are all in rough agreement the result is reliable. But the sort of massive dating errors the creationists are talking about never occur.
A: The paper can be found at arXiv:1006.4848, titled "Power Spectrum Analysis of BNL Decay-Rate Data" by P.A. Sturrock, J.B. Buncher, E. Fischbach, J.T. Gruenwald, D. Javorsek II, J.H. Jenkins, R.H. Lee, J.J. Mattes, J.R. Newport.
Neutrinos have a very small probability of interacting with anything. State of the art detectors are lucky to catch one neutrino for every billion neutrinos that pass through them. High energy neutrinos are more likely to react than low energy ones.
Most of the neutrinos we detect on Earth are produced in the Sun. It's commonly said that if you sent a beam of neutrinos (with the same energy as solar neutrinos) through a light-year of lead only 50% of them would be absorbed. According to theory, the universe is full of neutrinos that were created during the Big Bang, but they've been red-shifted so they now have such low energy that we don't yet have the technology to detect them.
Neutrinos are intimately connected with beta decay. All forms of beta decay emit (or absorb) a neutrino or antineutrino (some rare forms may involve 2 neutrinos, this is an area of active research). So it's reasonable to suspect that the ambient neutrino flux could affect beta decay rates... except that neutrinos are notorious for their extremely low probability of reacting.
So when that paper by Sturrock, Fischbach et al was originally announced it was greeted with a little skepticism. In the intervening eight or so years, there have not been any independent studies corroborating their findings, and the consensus appears to be that the small variations in decay rates that they found are not due to variations in the solar neutrino flux.
From https://physicsworld.com/a/do-solar-neutrinos-affect-nuclear-decay-on-earth/

Karsten Kossert, a physicist at PTB, says that his own research, with others, on decay rates has shown that there are “some fluctuations in some instrument readings”. “However, since different instruments and/or measurement techniques show different variations, we can exclude solar neutrinos as a common reason for these variations.” He adds: “In some cases, we have shown a clear correlation between environmental parameters – such as temperature, humidity, air pressure – and instrument readings.”
Kossert recently co-authored a study looking at data on decay rates from 14 laboratories around the world. The report concluded that “observed seasonal modulations can be ascribed to instrumental instability” and that “there are also no apparent modulations over periods of weeks or months”.

But even if these beta decay rate variations were due to variations in the solar neutrino flux, that wouldn't imply that the beta decay rates were radically different in the past. Remember, we're talking about rate variations of less than one percent. For decay rates to be significantly faster in ancient times would require a much higher (&/or more energetic) neutrino flux in the past, which would imply that the reaction rate in the Sun's core was much faster in the past. But that doesn't make much sense: the Sun is gradually getting warmer, not cooler. (This analysis is complicated by the fact that neutrinos travel from the solar core to its surface in less than 2.5 seconds, but it takes heat a million years or so to propagate from the Sun's core to its surface).
