Medium and high spin states of the Y96 nucleus, located in the shape-coexistence region near Z=40 and N=60, were populated in thermal-neutron-induced fission of U233 and U235 targets, diluted in a scintillator. γ rays were measured with the FIssion Product Prompt γ-ray Spectrometer (FIPPS) high-purity germanium (HPGe) detector array, using double and triple γ-ray coincidence techniques and taking advantage of the efficient fission tag provided by the scintillating target material. A complex level scheme, extending up to 5.2 MeV and including excitations above the 8+β-decaying isomer, was investigated, and firm spin and parity assignments were given to a number of states, on the basis of angular correlation analysis and considerations on the γ-decay patterns. While the structures built on the 0− ground state and the 8+ isomer show irregular patterns typical for spherical shapes, the (6+) isomeric state at 1655 keV [with half-life of 181(9) ns], and the rotational band built on it [with spin-parity values between (6+) and (9+)], can be explained by Hartree-Fock-Bogoliubov calculations, if an oblate deformation is assumed. This is the first observation of a deformed structure in an N=57 isotone, lying three neutrons away from the N=60 line. An important finding is also the 115-keV transition which connects the (6+) 181(9)-ns isomer to the β-decaying 8+ spherical isomer, allowing us to firmly place the latter at 1541 keV excitation energy. This may be relevant for calculations of electron and antineutrino spectra from fission of actinides, for which Y96 is a prominent product.

中文翻译：

---

Y96同位素的γ谱：在N=60之前寻找形状共存的开始

Y96 原子核的中高自旋态位于 Z=40 和 N=60 附近的形状共存区域，填充在 U233 和 U235 靶标的热中子诱导裂变中，并在闪烁体中稀释。γ 射线是通过 FIssion Product Prompt γ 射线光谱仪 (FIPPS) 高纯锗 (HPGe) 探测器阵列测量的，使用双和三重 γ 射线符合技术并利用闪烁目标材料提供的高效裂变标签。研究了扩展至 5.2 MeV 并包括高于 8+β-衰变异构体的激发的复杂能级方案，并基于角相关分析和对γ-衰变模式。虽然建立在 0− 基态和 8+ 异构体上的结构显示出典型的球形不规则图案，但 1655 keV 的 (6+) 异构态 [半衰期为 181(9) ns]，以及旋转带建立在它之上 [自旋奇偶性值介于 (6+) 和 (9+) 之间]，可以通过 Hartree-Fock-Bogoliubov 计算来解释，如果假设扁形变形。这是对 N=57 等位线中变形结构的首次观察，距离 N=60 线三个中子。一个重要的发现也是 115-keV 跃迁，它将 (6+) 181(9)-ns 异构体连接到 β-衰变 8+ 球形异构体，使我们能够将后者牢固地置于 1541 keV 激发能。这可能与计算来自锕系元素裂变的电子和反中微子光谱有关，其中 Y96 是一个突出的产品。