Search for Particle-Bound Polyneutron Systems

A search for particle-bound polyneutron systems (${}_{}{}^6{}_{}{}^{}n-{}_{}{}^{12}{}_{}{}^{}n$) produced in ∼ 700-MeV proton interactions with uranium has yielded negative results. A radiochemical technique was used. The limits on production cross section—${10}^{-3\mathrm{}}$ to ${10}^{-5\mathrm{}}$ μb—are many orders of magnitude lower than previous limits at comparable energies, are lower than predictions based on extrapolation of yields of other neutron-rich species, and are in contrast to the positive results reported recently from work with 24-GeV protons on tungsten.