Collectivity of neutron-rich palladium isotopes and the valence proton symmetry

Absolute transition probabilities for the first $2^{+}$ states in ${}^{110,114}\mathrm{Pd}$ were measured using the recoil distance Doppler shift technique following projectile Coulomb excitation at intermediate beam energy. This technique was applied for the first time to projectiles produced in a primary fragmentation reaction, which get Coulomb excited in a secondary reaction. The ${}^{110}\mathrm{Pd}$ data was used to check the novel experimental technique as well as the data analysis procedure, which is based on the examination of $\gamma$-ray line shapes. Whereas the measured $B(E2)$ value for ${}^{110}\mathrm{Pd}$ agrees very well with the literature, the value obtained for ${}^{114}\mathrm{Pd}$ differs considerably. The new experimental data are compared to calculations in the framework of the Interacting Boson Model. The data are also used to test the novel concept of valence proton symmetry, which allows for extrapolation of nuclear properties to very neutron-rich nuclei.

Figure 1

Systematics of $B(E2,0_1^{+}\to 2_1^{+})$ values in Pd (dots), Cd (squares), and Ru (triangles) nuclei. The $B(E2,0_1^{+}\to 2_1^{+})$ values for ${}^{112,114}\mathrm{Pd}$ are taken from Ref. [7], others are taken from [20]. Also given are the Grodzins estimates for Pd as a solid curve.

Figure 2

Simultaneous fit of spectra at forward and backward angles in ${}^{114}\mathrm{Pd}$. Shown are the data and fits for the SeGA rings at ${30}^{°}/{140}^{°}$. The corresponding target-degrader separations are indicated. The Doppler corrections account for the detector segmentation but not for the angular position of the detector in the array.

Figure 3

$B(E2,0_1^{+}\to 2_1^{+})$ values of Pd isotopes (dots) compared with scaled values of the corresponding Xe VPS partners (open triangles) using the scaling factor $S=(Z_{\mathrm{Pd}}/Z_{\mathrm{Xe}}){}^2*(A_{\mathrm{Pd}}/A_{\mathrm{Xe}}$). Open squares correspond to values for ${}^{112,114}\mathrm{Pd}$ taken from Ref. [22]. In addition, the scaled $B(E2)$ values according to relation (1) are given as a dashed line. See also text.

Figure 4

Spectra and $B(E2)$ values of ${}^{110,114,118}\mathrm{Pd}$ compared to IBM calculations. Numbers given at the arrows are $B(E2)$ values in units of $e^2{b}^2$.