In the case of lava flow, we know that all surface substance is subject to radiation from the sun and other sources. Neutron bombardment speeds up nuclear decay of the unstable isotopes. This fact allows us to generate heat in a nuclear reactor.
Have you run the numbers on this? At this hand waving level it is meaningless.
Neutron bombardment speeds up nuclear decay of the unstable isotopes.
You know better than I do about this but that statement is, in this context, incorrect I think.
It does not speed up the decay of a particular isotope at all. It changes the isotope being considered. And that isotope decays just as it would (well, once the nucleus stops "ringing" from the collesion).
The numbers you need concern the amount of radiation that reaches the sample in situ, cross sections etc. If you are going to just speculate with arm waving then you are not really giving reasonable consideration to this at all.
As noted, independent methods arrive at consistent results in the vast majority of cases. If you conjure up possible problems you have to consider that the answer is that they aren't problems unless you can also explain why the problem is problematic across all methods.
You need to be able to keep that in mind. Always come back to that.