Lithium-4

Lithium-4 contains three protons and one neutron. It is the shortest-lived known isotope of Lithium, with a half-life of 91±9 yoctoseconds ((9.1±0.9)×10⁻²³ s) and decays by proton emission to Helium-3. Lithium-4 can be formed as an intermediate in some nuclear fusion reactions.