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All stable nuclei and known radioactive nuclei, both naturally occurring and manmade, are shown on this chart, along with their decay properties.
In this case the nucleus can decay by getting rid of its excess energy without changing Z or N by emitting a gamma ray.Of the nuclei found on Earth, the vast majority are stable.This is so because almost all short-lived radioactive nuclei have decayed during the history of the Earth.There are approximately 270 stable isotopes and 50 naturally occurring radioisotopes (radioactive isotopes).Thousands of other radioisotopes have been made in the laboratory.Nuclear decay processes must satisfy several conservation laws, meaning that the value of the conserved quantity after the decay, taking into account all the decay products, must equal the same quantity evaluated for the nucleus before the decay.
Conserved quantities include total energy (including mass), electric charge, linear and angular momentum, number of nucleons, and lepton number (sum of the number of electrons, neutrinos, positrons and antineutrinoswith antiparticles counting as -1).
The probability that a particular nucleus will undergo radioactive decay during a fixed length of time does not depend on the age of the nucleus or how it was created.
Radioactive decay will change one nucleus to another if the product nucleus has a greater nuclear binding energy than the initial decaying nucleus.
The difference in binding energy (comparing the before and after states) determines which decays are energetically possible and which are not.
The excess binding energy appears as kinetic energy or rest mass energy of the decay products.
The Chart of the Nuclides, part of which is shown above is a plot of nuclei as a function of proton number, Z, and neutron number, N.