Rare fission processes.

In nuclear fission, the splitting of an unstable atomic nucleus typically produces two moderate-size fragments and a number of neutrons. Akunuri V. Ramayya of Vanderbilt University in Nashville and his collaborators have discovered that, in addition to normal spontaneous fission, the isotope californium-252 occasionally splits in two in such a way that no neutrons are released. Measurements taken with the Gammasphere detector at the Lawrence Berkeley (Calif.) National Laboratory indicate that this rare process, known as neutronless binary fission, occurs only 1 to 10 times per 10,000 fission events.

Ramayya and his coworkers have also found that californium-252 sometimes breaks into three fragments--two of moderate size and one as small as a helium nucleus (or alpha particle). These findings provide significant insights into fission processes, Ramayya says. Theorists are now trying to formulate explanations of the newly observed phenomena.