Mike Results—Implications for Spontaneous Fission

The November 1, 1952, thermonuclear explosion "Mike" produced isotopes through mass number 255. Since neutron irradiation time is short compared with possible beta-decay lifetimes, we conclude that, through $A=255\mathrm{}$, nuclei far from the line of beta stability on the neutron-rich side are at least as likely to decay by negatron emission as by spontaneous fission.