Uraniums abbreviation is U, so uranium-238 can be more briefly written as U238.

different radiometric dating techniques-20different radiometric dating techniques-85

The mass number doesnt change, while the atomic number goes down by 1.

So an atom of potassium-40 (K40), atomic number 19 can absorb an electron to become an atom of argon-40 (Ar40), atomic number 18.

The rules are the same in all cases; the assumptions are different for each method.

To explain those rules, I'll need to talk about some basic atomic physics. Hydrogen-1's nucleus consists of only a single proton.

Thus, an atom of carbon-14 (C14), atomic number 6, emits a beta particle and becomes an atom of nitrogen-14 (N14), atomic number 7.

A third, very rare type of radioactive decay is called electron absorption.

Some nuclides have very long half-lives, measured in billions or even trillions of years.

Others have extremely short half-lives, measured in tenths or hundredths of a second.

Some, however, are unstable -- given time, they will spontaneously undergo one of the several kinds of radioactive decay, changing in the process into another element.

There are two common kinds of radioactive decay, alpha decay and beta decay.

The decay rate and therefore the half-life are fixed characteristics of a nuclide. Thats the first axiom of radiometric dating techniques: the half-life of a given nuclide is a constant.