Physicists find signs of four-neutron nucleus
Potential existence of ‘tetraneutron’ defies theoretical expectations
NO PROTONS ALLOWED The collision of two varieties of helium nuclei at a Japanese lab produced beryllium nuclei and tetraneutrons, nuclei with four neutrons but no protons. This illustration depicts the number of protons and neutrons but not their actual positions within each nucleus.
Source: APS; Credit: J. Hirshfeld