Any incoming negative charge would be deflected by the electron shell and any positive charge that penetrated the electron shells would be deflected by the positive charge of the nucleus itself. "Decay" simply refers to a meson or baryon becoming another type of particle, as the number of a certain type of particle goes down or decays as they are converted.This can happen due to one of three forces or "interactions": strong, electromagnetic, and weak, in order of decreasing strength.However, the nucleus has a strong positive charge and the electron shells have a strong negative charge.
Carbon, on the other hand, with a shorter mean lifetime of over 8000 years, is more useful for dating human artifacts.
With uranium-lead dating, for example, the process assumes the original proportion of uranium in the sample.
One assumption that can be made is that all the lead in the sample was once uranium, but if there was lead there to start with, this assumption is not valid, and any date based on that assumption will be incorrect (too old).
For example, a neutron-deficient nucleus may decay weakly by converting a proton in a neutron (to conserve its positive electric charge, it ejects a positron, as well as a neutrino to conserve the quantum lepton number); thus the hypothetical atom loses a proton and increments down the table by one element.
A complex set of rules describes the details of particle decays: historically, the finding of which as been a major objective of particle physics.
The second way that a nucleus could be disrupted is by particles striking it.