U235n

U235n is not a standard designation in established nuclear nomenclature. In many contexts, the term may be encountered as an informal or context-specific label and can be ambiguous without additional information. Commonly, it might be interpreted as referring to a uranium-235 nucleus in association with an extra neutron (i.e., a neutron-rich situation) or to a particular neutron configuration around a uranium-235 core. Because isotope labels in science follow fixed mass numbers, a precise meaning for U235n depends on the source and should be clarified.

In standard nuclear physics, uranium-235 (235U) is a naturally occurring, fissile isotope of uranium with 92 protons and 143 neutrons. Its nuclei are capable of sustaining a nuclear chain reaction when absorbing thermal neutrons, a property central to both civilian nuclear reactors and some weapons designs. 235U has a very long intrinsic half-life on the order of hundreds of millions of years and decays by alpha emission to thorium-231, though in reactor conditions it primarily undergoes fission rather than spontaneous decay.

If one interprets U235n as a neutron-rich variant, such isotopes would have mass numbers greater than 235 (for example, 236U and beyond). These neutron-rich uranium isotopes are typically unstable and decays or transmute via beta emission or fission on timescales ranging from microseconds to years, depending on the specific isotope. Neutron-rich uranium isotopes are usually produced only under specialized conditions in reactors or accelerators and are not found in significant quantities in nature.

Overall, U235n does not correspond to a widely recognized, stable isotope, and its precise properties depend on the intended definition provided by the source using the notation.