One example of this can be found in metamorphic rocks.
This does not mean that all rock samples are unreliable, but it is possible to account for a process which throws off the data for metamorphic rocks.
For these reasons, if a rock strata contains zircon, running a uranium-lead test on a zircon sample will produce a radiometric dating result that is less dependent on the initial quantity problem.
There are a number of implausible assumptions involved in radiometric dating with respect to long time periods.
One key assumption is that the initial quantity of the parent element can be determined.
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.
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.
However, the nucleus has a strong positive charge and the electron shells have a strong negative charge. Those that can decay are mesons and baryons, which include protons and neutrons; although decays can involve other particles such as photons, electrons, positrons, and neutrinos.
This interpretation unfortunately fails to consider observed energetic interactions, including that of the strong force, which is stronger the electromagnetic force.
It is important that the sample not have had any outside influences.
Radiometric dating is a method of determining the age of an artifact by assuming that on average decay rates have been constant (see below for the flaws in that assumption) and measuring the amount of radioactive decay that has occurred.