Excited states have been observed for the first time in the very neutron-deficient odd-odd nucleus La. The observed rays have been assigned based on coincidences with lanthanum X rays measured with the 3 array and with fusion-evaporation residues measured with the separator. The observed rays form a rotational band which decays to the ground state via a cascade of four low-energy transitions. Based on the systematic comparisons with the heavier odd-odd La isotopes we assign spin-parity to the ground state and a configuration to the rotational band. The nuclear shape has been investigated by the cranked Nilsson-Strutinsky model. Two quasiparticle plus triaxial rotor model calculations including the interaction nicely reproduce the spin of the inversion between the even- and odd-spin cascades of 2 transitions, giving credit to the interaction as an important parameter responsible for the mechanism inducing the inversion. The position of the Fermi levels, in particular for neutrons, also has a strong impact on the observed inversion in the chain of lanthanum nuclei.

中文翻译：

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首次观察到 120La 激发态及其对 A ≈ 120 质量区域形状演化的影响


首次在极度缺乏中子的奇奇核 La 中观察到激发态。观察到的射线是根据与 3 阵列测量的镧 X 射线和分离器测量的聚变蒸发残留物的重合来分配的。观测到的射线形成一个旋转带，通过四个低能跃迁的级联衰减到基态。基于与较重的奇奇 La 同位素的系统比较，我们将自旋宇称分配给基态并将构型分配给旋转带。核形状已通过曲柄尼尔森-斯特鲁廷斯基模型进行了研究。两个准粒子加三轴转子模型计算（包括相互作用）很好地再现了两个跃迁的偶数自旋级联和奇数自旋级联之间的反转自旋，将相互作用视为导致反转机制的重要参数。费米能级的位置，特别是中子的费米能级位置，也对观察到的镧核链的反转有很大影响。