3.1-HOUR Y$sup 90$m

A 3.1-hr isomer, Y/sup 90m/, was produced by neutron capture in yttrium. The isomeric transition consists of two coincident gamma rays of nearly equal intensity and energies, 203 kev and 480 kev, Mass and atomic number assignment was made by cross bombardment and chemical separations. Modes of preduction were Y/sup 89/(n, gamma )Y/sup 90m/ (thenmal and epicadmium neutrons) and Nb/sup 93/ (n, alpha )Y/sup 90m/m, and Zr/sup 90/ (n,p)Y/sup 90m/ (14-Mev neutrons). (auth)