A graph of the number of neutrons versus the number of protons for all stable naturally occurring nuclei.
Nuclei that lie to the right of this band of stability are neutron poor; nuclei to the left of the band are neutron-rich.
It can capture an electron or it can emit a positron.
Electron emission therefore leads to an increase in the atomic number of the nucleus.
Neutron-poor nuclides with atomic numbers less than 83 tend to decay by either electron capture or positron emission.
Many of these nuclides decay by both routes, but positron emission is more often observed in the lighter nuclides, such as A third mode of decay is observed in neutron-poor nuclides that have atomic numbers larger than 83.
Although it is not obvious at first, -decay increases the ratio of neutrons to protons.
Consider what happens during the -decay of The difference between the mass of an atom and the sum of the masses of its protons, neutrons, and electrons is called the mass defect.
Neutron-poor nuclides decay by modes that convert a proton into a neutron.
When they die no new carbon-14 is taken in by the dead organism.
The carbon-14 it contained at the time of death decays over a long period of time.
Later called Ötzi the Iceman, small samples from his body were carbon dated by scientists.
The results showed that Ötzi died over 5000 years ago, sometime between 33 BC. Uranium has a very long half-life and so by measuring how much uranium is left in a rock its approximate age can be worked out.