[9][10][11] Beyond these stable forms, 32 artificial unstable isotopes and various isomers have been studied, the longest-lived of which is 127Xe with a half-life of 36.345 days.
The shortest-lived isotope, 108Xe,[12] has a half-life of 58 μs, and is the heaviest known nuclide with equal numbers of protons and neutrons.
129Xe is produced by beta decay of 129I (half-life: 16 million years); 131mXe, 133Xe, 133mXe, and 135Xe are some of the fission products of both 235U and 239Pu, so are used as indicators of nuclear explosions.
This was discovered in the earliest nuclear reactors built by the American Manhattan Project for plutonium production.
For the same reason, the fission products produced in a nuclear explosion and a power plant differ significantly as a large share of 135Xe will absorb neutrons in a steady state reactor, while basically none of the 135I will have had time to decay to xenon before the explosion of the bomb removes it from the neutron radiation.
[citation needed] The concentrations of these isotopes are still usually low compared to the naturally occurring radioactive noble gas 222Rn.
It has a half-life of about 9.2 hours and is the most powerful known neutron-absorbing nuclear poison (having a neutron absorption cross-section of 2 million barns[21]).