Microscopic structure of the one-phonon 2+ states of Po208

Abstract

The lifetimes of the 2 + 1 and 4 + 1 states of 208 Po were measured in the α-transfer reaction 204 Pb( 12 C, 8 Be) 208 Po by γ-ray spectroscopy utilizing the recoil distance Doppler Shift method. The newly extracted transition strengths alongside with ones of the decay of 2 + 2 state were compared to the results of large-scale shell-model calculations using an effective interaction derived from the realistic CD-Bonn nucleon-nucleon potential. The comparison indicates the importance of the quadrupole isovector excitations in the valence shell for a fine tuning of the two-body matrix elements of the shell-model interaction.

Study the structure of the low-lying states of 206Po

“…The calculated excitation energies of the yrast states are in a very good agreement with the experimental data, as the discrepancies are less than 80 keV for all of the states. The comparison of the B(E2) transition strengths shows very good agreement for the  + + ( ) = 388 e 2 fm 4 [9]. This allows us to conclude that the increase of the neutron holes in N = 126 shell closure increases the collectivity of the + 2 1 states.…”

“…The remaining 24.8% of the intensity of the 701-keV transition is considered as direct population of the + 2 1 state. Since the + 3 1 ( ) state could not be considered neither as fast nor as slow feeder we have assumed these two limits and we accounted for their influence in our analysis in a similar way as in our previous studies [9,22]. Firstly, if we assume that its lifetime is short enough so that it decays only in flight, no further corrections of the intensities of the 701-keV transition are needed.…”

“…For the purpose of these calculations, the double-magic nucleus 208 Pb has been considered as a closed inert core. The calculations are performed in a similar way as in our previous studies of 208,209 Po [7,9]. For both proton particles and neutron holes the model space included the orbitals 2p 3/2 , 2p 1/2 , 1f 7/2 , 1f 5/2 , 0h 9/2 , 0i 13/2 .…”

“…For both proton particles and neutron holes the model space included the orbitals 2p 3/2 , 2p 1/2 , 1f 7/2 , 1f 5/2 , 0h 9/2 , 0i 13/2 . As in our studies [7,9], the Q ˆ-box folded-diagram approach [24] was used for the two-body matrix elements of the effective Hamiltonian. The starting point here is the CD-Bonn nucleon-nucleon potential [25] renormalized utilizing the V low−k approach [26] (henceforth these calculations will be labelled as CD-Bonn calculations).…”

“…A suitable region for such investigations is the region of Po isotopes nortwest of 208 Pb. In the last decade, the nuclei within this region have been subject to renewed scientic interest [6][7][8][9][10]. The energy spacing between the yrast 2 + , 4 + , 6 + , and 8 + states in 210 Po suggests a seniority-like structure.…”