Search for Isovector Valence-Shell Excitations in $^{140}$Nd and $^{142}$Sm via Coulomb excitation reactions of radioactive ion beams

Projectile Coulomb excitation experiments were performed at HIE-ISOLDE at CERN with the radioactive ion beams of $^{140}$Nd and $^{142}$Sm. Ions with an energy of 4.62 MeV/A were impinging on a 1.45 mg/cm$^2$ thick $^{208}$Pb target. The $\gamma$-rays depopulating the Coulomb-excited states were recorded by the HPGe-array MINIBALL and scattered particles were detected by a double-sided silicon strip detector. Experimental intensities were used for the determination of electromagnetic transition matrix elements. A preliminary result of the $B(M1; 2^+_3 \rightarrow 2^+_1)$ of $^{140}$Nd and an upper limit for the case of $^{142}$Sm are revealing the main fragments of the proton-neutron mixed-symmetry $2^+_{1,ms}$ states.