The lifetimes of the low-lying excited states $2^+$ and $4^+$ have been directly measured in the neutron-deficient $^{106,108}$Sn isotopes. The nuclei were populated via a deep-inelastic reaction and the lifetime measurement was performed employing a differential plunger device. The emitted $\gamma$ rays were detected by the AGATA array, while the reaction products were uniquely identified by the VAMOS++ magnetic spectrometer. Large-Scale Shell-Model calculations with realistic forces indicate that, independently of the pairing content of the interaction, the quadrupole force is dominant in the $B(E2; 2_1^+ \to 0_{g.s.}^+)$ values and it describes well the experimental pattern for $^{104-114}$Sn; the $B(E2; 4_1^+ \to 2_1^+)$ values, measured here for the first time, depend critically on a delicate pairing-quadrupole balance, disclosed by the very precise results in $^{108}$Sn. This result provides insight in the hitherto unexplained $B(E2; 4_1^+ \to 2_1^+)/B(E2; 2_1^+ \to 0_{g.s.}^+) < 1$ anomaly.

中文翻译：

---

中子缺陷锡核中的配对四极杆相互作用：106,108Sn 中低位态的首次寿命测量

在缺乏中子的 $^{106,108}$Sn 同位素中直接测量了低位激发态 $2^+$ 和 $4^+$ 的寿命。通过深度非弹性反应填充原子核，并使用差分柱塞装置进行寿命测量。发射的$\gamma$射线由AGATA阵列检测，而反应产物由VAMOS++磁谱仪唯一识别。具有现实力的大规模壳模型计算表明，与相互作用的配对内容无关，四极力在 $B(E2; 2_1^+ \to 0_{gs}^+)$ 值中占主导地位，并且很好地描述了 $^{104-114}$Sn 的实验模式；此处首次测量的 $B(E2; 4_1^+ \to 2_1^+)$ 值严重依赖于微妙的配对四极平衡，$^{108}$Sn 中非常精确的结果揭示了这一点。这一结果提供了对迄今为止无法解释的 $B(E2; 4_1^+ \to 2_1^+)/B(E2; 2_1^+ \to 0_{gs}^+) < 1$ 异常的洞察。