Yield ratio for the two 241Pu fission isomers in the 242(γ, n) reaction

The half-lives and yield ratios for the two 241 Pu fission isomers have been measured in the 242 Pu(γ, n) reaction. The observed half-life for the long-lived isomer (T 1 2 = 20.5 ± 2.2 μs) is in agreement with previous data, and the existence of a short-lived 34 ± 7 ns isomer in 241 Pu could be confirmed. The measured yield ratios are Y iso / Y pr = (9.2 ± 0.8) × 10 −5 and Y iso / Y pr = (3.7 ± 0.7) × 10 −5 , respectively. From a statistical model analysis of the isomeric fission yield ratio, Y long iso / Y short iso = 2.5 ± 0.6, a spin assignment for the two isomers is attempted. Possible spin combinations are compared with single-particle shell-model calculations and with available spectroscopic data for the other even-odd Pu isotopes.