Different dating methods use different elements with differnt decay mechanisms. I would say that the fact that different dating methodes are all able to date a given sample with the same age argues strongly for a constant decay rate. I think it would be highly unlikely that your bombardment of particles would have the same effect on all 3(4?) differnt decay mechanisms.
On the otherhand there are far more qualified persons on this board to answer this, so if I were u I would have more faith in their answers. This is just my guess
[This message has been edited by dinoflagulates, 05-10-2003]