67Xe

67Xe, or xenon-67, is the hypothetical isotope of the element xenon (atomic number 54) with mass number 67. If it existed as a bound nucleus, it would contain 54 protons and 13 neutrons. There are no confirmed observations or experimental measurements for this isotope, and it is not listed among the bound xenon isotopes in standard references.

Because its neutron-to-proton ratio is extremely low, 67Xe would lie far beyond the proton drip line. Nuclear mass models generally predict that such a light, proton-rich xenon isotope would be unbound, decaying almost instantaneously by proton emission or other fast decay channels. Consequently, no measured half-life or decay-energy data are available.

In theoretical discussions, isotopes like 67Xe help define the limits of nuclear binding and test models of the proton-rich side of the chart of nuclides. While some models permit speculative resonant states near the drip line, there is no experimental evidence for a bound 67Xe state as of now.