The even isotopes of mercury have been systematically studied using the Interacting Boson Model (IBM). In order to treat shape coexistence in the light isotopes, two separate IBM calculations were performed with different configurations, which were subsequently mixed. The four Hamiltonian parameters, which were allowed to vary freely from isotope to isotope, were found to be consistent with the corresponding IBM parameters used for platinum and osmium. Overall, the calculated energy spectra and electromagnetic properties are in reasonable agreement with experiment.

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Two new absolute transition rates are reported for the nucleus 144Sm following an (e,e') Coulomb excitation study. They are B(E3;3---+0+)=(38• and B(E1; 3---+2+)=(2.8__+0.4)x 10 .3 W.u. This large E1 matrix element, along with the previously known B(E1; 1----0 +) value support the interpretation of the 1-state in this nucleus as 2-phonon 2 + x 3-excitation. In the frame of the IBM-1 +f-boson model we show the need for a two-body term in the E1 transition operator. Estimates for the strengths of the one and two-body parts of the E 1 transition operator are obtained from these experimental data.PACS: 21.60.Ev; 23.20.CK; 27.60. +j Low-lying 1-states in nuclei in the N=82 region have been of interest for many years because of the large E1 strength seen in elastic photon scattering [1 3] and inelastic proton scattering [4]. The energies of these 1-states are slightly below the sum of the excitation energies of the lowest 2 + and 3-states, leading to their interpretation as two-phonon 2 + x 3-states [1,5]. Strong E1 transitions in the actinides have been explained variously in terms of stable octupole deformation [6] and collective dipole modes [7,8]. Such mechanisms might play a role in lighter nuclei also. In order to clarify the origin of the E 1 transitions in the N=82 region, it is of interest to look for other strong E 1 data in these nuclei.The 1448m nucleus offers a good possibility of obtaining the E 1 matrix element between the 2 + and 3-states [9]. The energy of the 3-state is 150 keV above that of the 2 + state (Fig. 1) and a branched decay of the 3-state to the 2 + and 0 + states has been reported [10,11]. In order to obtain the E1 transition rate we have measured an absolute B(E3) matrix element from the 3-state to the gs by (~, e') Coulomb excitation of a thin (1 mg/cm2), 89% en- where B(EL)) are measured in (e fmC) 2.From the partial level scheme shown in Fig. i, one can see that the above excitation ratio must be the same as the decay expression 1/1'= (I(3 -~ 0 +) + 1(3 ----, 2 +))/ (I(2 + ~ 0 +) --1(3 -~ 2+))where I's are the relative intensities of the corresponding 7-rays. Our measured value for this ratio is 0.22+0.02 (including the internal conversion coefficient ~=0.09 for the 3----r2 + transition [13]). By using the value B(E2; 0 + ~ 2+) =(2.66_+ 0.08)

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