Possible observation of light neutron nuclei in the alpha-particle-induced fission of $^{238}$U

Searches for nuclear-stable multineutrons among products originating from the fission of $^{238}$U nuclei that is induced by 62-MeV alpha particles were performed by the activation method. The reaction involving the transfer of four neutrons and occurring on the isotope $^{88}$Sr, $^{88}$Sr(${}^xn,(x-4)n){}^{92}$Sr${}\to{}^{92}$Y, was used to identify nuclear-stable multineutrons. A line at the energy of $E = 1384$ keV was found in the measured gamma-ray spectra of irradiated samples. This line, together with the measured time dependence of the decrease in its activity, is indicative of the formation of the beta-active nucleus $^{92}$Sr. This result was reproduced in repeated measurements. It suggests the possible existence of nuclear-stable multineutrons $({}^xn)$ for $x\geq6$. The differential cross section for the ${}^xn$ yield at an angle of $30^\circ$ in the alpha-particle-induced fission of $^{238}$U was about $\sim6\cdot10^{-2}\,$ mb/sr.