SUCCESSIVE DECAYS FROM Pr137 AND Ce137m: DECAY OF ADJACENT PRASEODYMIUM ISOTOPES

Abstract

The decay of Pr¹³⁷ entirely to a 9.0-hour ground state of Ce¹³⁷ was independently discovered. By allowed electron capture, Ce¹³⁷ decays predominantly to a low-lying state of La¹³⁷, with only a 3% branching to a 440-kev excited state. The 440-kev transition is at least predominantly E2 in character.A 34.4-hour isomeric state produced by the La¹³⁹(p, 3n)Ce^137m reaction decays by a 254.5-kev M4 transition to the 9-hour -ground state. A 0.6% branching was found from the isomeric state directly to a small group of apparently high spin states in La¹³⁷.Studies of mass-separated isotopes confirmed the existence of 1.5-hour Pr¹³⁷ and 1.0-hour Pr¹³⁶. The K-capture to positron branching ratios observed in the decay of Pr¹³⁹, Pr¹³⁸, Pr¹³⁷, and Pr¹³⁶ show that these isotopes decay by allowed transitions to their cerium daughters. Characteristic gamma rays were observed.