Shift of the 2₁⁺ state of ¹⁰Be in ternary cold fission of ²⁵²Cf

Recent experimental data indicate that in the ternary cold fission of ²⁵²Cf the energy of the first excited state of the accompanying light cluster ¹⁰Be is decreased by an amount ranging between ≈ 6 and 26 keV. A model is proposed to calculate the shift of the vibrational 2₁⁺ state in ¹⁰Be when its heavy companions are the even-even nuclei ¹⁴⁶Ba and ⁹⁶Sr. The stiffness parameters of the β vibrations are calculated within the self-consistent Hartree-Fock method with BCS pairing correlations taken into account, and their change is determined by the interaction of the light cluster with the heavy fragments. The results point to a dependence of the shift magnitude and signature on the relative distance between the three clusters and their mutual orientation. Eventually it is the anharmonic perturbation of the spherical vibrator which is responsible for obtaining a negative energy shift of the 2₁⁺ state.