is. 8He and 14Be both exhibit a four-neutron halo. Nuclei that have a proton halo include 8B and 26P. A two-proton halo is exhibited by 17Ne and 27S. Proton halos are expected to be rarer and more unstable than neutron halos because of the repulsive forces of the excess proton(s). See also Halo nuclei and nuclear force range limits Isotopes of lithium Lithium Exotic atom Borromean nucleus References Further reading Nuclear physics