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.
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.
Uraniums abbreviation is U, so uranium-238 can be more briefly written as U238.
Many nuclides are stable -- they will always remain as they are unless some external force changes them.
In other words, electron absorption is the exact reverse of beta decay.I found several good sources, but none that seemed both complete enough to stand alone and simple enough for a What is radiometric dating?Simply stated, radiometric dating is a way of determining the age of a sample of material using the decay rates of radio-active nuclides to provide a 'clock.' It relies on three basic rules, plus a couple of critical assumptions.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.(Note that this doesnt mean the half-life of an element is a constant.Since all atoms of the same element have the same number of protons, different nuclides of an element differ in the number of neutrons they contain.For example, hydrogen-1 and hydrogen-2 are both nuclides of the element hydrogen, but hydrogen-1's nucleus contains only a proton, while hydrogen-2's nucleus contains a proton and a neutron.The half-life of a radioactive nuclide is defined as the time it takes half of a sample of the element to decay.A mathematical formula can be used to calculate the half-life from the number of breakdowns per second in a sample of the nuclide.After emission, it quickly picks up two electrons to balance the two protons, and becomes an electrically neutral helium-4 (He4) atom. When an atom emits a beta particle, a neutron inside the nucleus is transformed to a proton.The mass number doesn't change, but the atomic number goes up by 1.