Investigation of 121I levels observed in the ( 3He, 3n) reaction

Abstract

Excited states of the odd-proton nuclide 121I have been investigated in the 121Sb( 3He, 3n) reaction. The level scheme, spin and parity assignments are based on results obtained from measurements of singles γ-ray spectra, excitation functions, γγ coincidences, γ-ray angular distributions and of delayed γ-rays. Levels up to 3274 keV excitation energy and spin values up to 27 2 were observed. Two isomeric states at 433.8 keV and 2353.1 keV were identified having half-lives of 10.0(4) ns and 80(12) ns, respectively. For the 2353.1 keV isomeric state the g-factor was determined as g = 1.20(10). Three / dGJ = 2 decoupled bands were observed built on the 5 2 + g.s. , 7 2 + 1 and 11 2 (−) 1 states. In addition a ΔJ = 1 band based on the 9 2 + 1 state was found which shows the properties of a strongly coupled rotational band. Potential energy surfaces of blocked single-proton states in 121I were calculated in the framework of the Strutinsky shell correction method. Level spacings within the K π = 9 2 + band were analysed in an angular momentum projection and a triaxial rotor approach. The results are compared with similar 9 2 + bands in neighbouring I and Sb nuclides confirming the assumption of an axially symmetric shape for I nuclei. The level scheme of 121I is compared with calculations performed in the core-quasiparticle coupling model including polarization effects due to the extra particle. Using the additivity of effective magnetic moments the three-particle configuration [π( g 9 2 ) −1( d 5 2 )( g 7 2 )] 21 2 + has been deduced for the isomeric ( 21 2 + ) state at 2353.1 keV.