Antiproton in the Nuclear Halo
The antiproton is a mirror twin of the proton: same mass, but negative charge. When it approaches an atomic nucleus, the particles can annihilate, turning into radiation.
Nuclei with a Heavy Guest
The phi meson is a particle that lives only for an instant, but it can briefly stick to protons and neutrons in an atomic nucleus. Physicists have studied what happens if such a meson finds itself inside light nuclei of helium and hydrogen.