Radiations of Mo⁹⁰ and the isomeric states of Nb⁹⁰

Abstract

Gamma-gamma coincidence measurements of the radiations of 5.7-hour Mo⁹⁰ showed that the 120- and 250-kev gamma rays previously reported by Diamond were delayed. Further experiments showed the existence of a 24-second isomer of Nb⁹⁰ emitting 120-kev gamma rays and a 10 to 20 millisecond isomer emitting 250-kev gamma rays. The transition types were not assigned unambiguously but the 24-second isomer is probably E2 and the 10 to 20 millisecond isomer E3 or M3 in nature. The radiations of the 14.6-hour ground state of Nb⁹⁰ were also studied. The 140-kev and 1.14-Mev gamma rays are in coincidence with each other and with annihilation radiation. A prominent 2.2-Mev gamma ray is not in coincidence with annihilation radiation or x-rays. Hence, it must be a delayed transition with ΔI≥3. This is of interest because of the rarity of such transitions in even-even nuclei.