Search for density isomers by observation of multiple emission of delayed neutrons in bombardment of Fe, Sn, and Pb by relativistic /sup 4/He and /sup 12/C nuclei

We have looked for delayed neutron emission from targets of Fe, Sn, and Pb irradiated by 44-GeV carbon ions and from Sn and Pb targets in bombardment by 5.04-GeV /sup 4/He ions. The purpose of the work was to search for cases of multiple emission of delayed neutrons by isomers with high excitation energies (for example, density isomers). Triple emission of delayed neutrons with a delay of more than 1 sec was not observed with the following upper limits of the cross section for production of the emitters: 6.8x10/sup -30/ cm/sup 2/ for the reaction Sn+/sup 4/He, 3.4x10/sup -29/ cm/sup 2/ for Pb+/sup 4/He, 4.5x10/sup -30/ cm/sup 2/ for Fe+/sup 12/C, 2.7x10/sup -29/ cm/sup 2/ for Sn+/sup 12/C, and 1.1x10/sup -28/ cm/sup 2/ for Pb+/sup 12/C.