New information on the $T_{1/2}$ = 47 s isomer in the $^{136}I$ nucleus

The $^{136}$I nucleus, populated in the spontaneous fission of $^{248}$Cm, was studied by means of prompt γ-ray spectroscopy using the EUROGAM2 array. The observation in this work of the 42.6 keV prompt-$\gamma$, M1 + E2 transition de-exciting the 7- level in $^{136}$I indicates that this level, interpreted as the $(\ensuremath \pi g_{7/2}^3 \nu f_{7/2})_{7^-}$ configuration, does not correspond to the T = 47s, β-decaying isomer in $^{136}$I. The isomer is placed 42.6keV below the 7- level. It has spin 6- and is interpreted as the $(\pi g_{7/2}^2 d_{5/2} \nu f_{7/2})_{6^-}$ configuration. This and other members of both multiplets can be reproduced properly only if one assumes that the $\pi d_{5/2}$ orbital in $^{136}$I is located 400 keV lower than in $^{133}$Sb. Possible mechanisms causing this effect are discussed