First glimpse of the elusive isotope nitrogen-9

Physicists might have spotted an elusive isotope of nitrogen that stretches the definition of a nucleus. Nitrogen-9’s nucleus is composed of a helium-like core of two protons and two neutrons, surrounded by five ‘unbound’ protons — a wildly unbalanced arrangement that stretches the nuclear glue of the strong force to breaking point. The five untethered protons quickly escape and the isotope lasts a mere 10⁻²¹ seconds. The boundary beyond which an isotope is too lopsided to live is called the ‘drip line’. If the evidence of ⁹N is confirmed, it will test the limit of just where the drip line might be.