Isomeric State of Po-212

An isomer of Po/sup 212/ with a half life of (45.1 plus or minus 0.6) sec and an excitation energy of 2.93 Mev has been positively identified by chendical and nuclear spectroscopic techniques. The isomer decays to known states of Pb/sup 208/ by the emission of alpha particles with energies and intensities of (11.65 plus or minus 0.02) Mev--97%, (9.08 plus or minus 0.015) Mev--(1.00 plus or minus 0.04)% and (8.52 plus or minus 0.015) Mev-- (2.05 plus or minus 0.09)% In coincidence with Po/sup 212m/ alpha particles, gamma rays with energies and intensities of (2.61 plus or minus 0.02) Mev--(2.6 plus or minus 0.3)% and (0.67 plus or minus 0.015) Mev-- ~ 2% were found. An immense alpha-decay hindrance factor for the 11.65-Mev group of 4 x 10/sup 13/ is explained by spin and parity assignments of 18+ for Po/sup 212m/= in conjunction with a theoretical shell-model analysis made by Glendenning. The alpha-particle energies and intensities of previously known alpha groups of Po/sup 211m/ STA(25.5 plus or minus 0.3) sec! were measured yielding values of (8.87 plus or minus 0.01) Mev--(7.04 plus or minus 0.015) Mev--91%. A new alpha group was found with an energy and intensity of (8.30more » plus or minus 0.015) Mev--(0.25 plus or minus 0.02)%. In coincidence with Po/sup 211m/ = alpha particles was a gamma ray of (O.90 plus or minus 0.015) Mev--(1.65 plus or minus 0.11)%. These Po/sup 211m/ = radiations are all consistent with the known energy level scheme of Pb/sup 207/. (auth)« less