Recent experimental data indicate that in the ternary cold fission of ${}^{252}\mathrm{Cf}$ the energy of the first excited state of the accompanying light cluster ${}^{10}\mathrm{Be}$ is decreased by an amount ranging between $\approx$ 6 and 26 keV. A model is proposed to calculate the shift of the vibrational $2_1^{+}$ state in ${}^{10}\mathrm{Be}$ when its heavy companions are the even-even nuclei ${}^{146}\mathrm{Ba}$ and ${}^{96}\mathrm{Sr}.$ The stiffness parameters of the $\beta$ 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 $2_1^{+}$ state.

• Received 2 December 1999

DOI:https://doi.org/10.1103/PhysRevC.61.041602