E. Lubkiewicz

The role of triaxiality in the ground states of even-even neutron-rich Ru isotopes

Abstract Partial decay schemes for the very neutron-rich nuclei 108,110,112 Ru and 114 Ru, about which nothing was previously known, have been determined from the study of prompt, triple-γ coincidences in 248 Cm fission fragments. Levels with probable spin up to 10ħ have been observed and γ-ray branching ratios obtained. Ratios of reduced electric quadrupole transition probabilities obtained from the branching ratios are in good agreement with predictions of a simple model of a rigid triaxial rotor.

Octupole correlations in neutron-rich, even-even barium isotopes

Abstract A = 140–148 even-even barium nuclei produced in the spontaneous fission of 248Cm were studied using the EUROGAM2 array. Spins and parities of excited levels have been firmly established from triple-γ angular correlation and direction-polarization correlation measurements. Known band structures have been extended and new bands were found. Band-crossing phenomena have been studied, which suggest termination of an alternating-parity band by particle alignment in 146Ba. The new data for 148Ba confirm predictions of a local decrease of electric dipole moment in 146Ba.

Properties of N=84, even-even nuclei populated in the spontaneous fission of 248Cm

Abstract: Excited states in the neutron-rich, N=84 nuclei 134Sn, 136Te and 138Xe, populated in the spontaneous fission of 248Cm, were studied to medium spins using the EUROGAM2 array. OXBASH code calculations support the experimental identification of maximum aligned configurations in these isotopes. Empirical shell model calculations agree with the proposed excitation energy of the neutron h9/2 excitation in the 132Sn region. A discrepancy between the observed and calculated excitation energy of the Iπ= 12+ level in 136Te indicates possible admixtures of collective excitations in this nucleus. Clear signs of collective excitations are observed in 138Xe.

Parities and multipolarities of gamma rays in neutron-rich odd-mass Ba nuclei

Abstract The nuclei 143,145,147 Ba produced in the spontaneous fission of 248 Cm have been studied using the EUROGAM phase II array. The parities and multipolarities of γ rays in these nuclei have been assigned from triple angular correlation, directional linear-polarisation correlation and internal conversion coefficient measurements. These data confirm an alternating-parity sequence connected by strong electric dipole transitions in 143 Ba. They also reveal a more weakly populated, complementary alternating-parity sequence. The two sequences together exhibit some characteristics of parity-doublet bands. Interpreting the E1 strengths in terms of a rotating intrinsic dipole moment gives a moment similar in size to that observed in 142 Ba and 144 Ba. No well-developed similar structure is seen in 145 Ba, although E1 transitions are observed, from which a value of the dipole moment is obtained. This value is smaller than the moment observed in 143 Ba. No features appropriate to strong octupole correlations were observed in 147 Ba.

Triple angular correlations of γ rays following spontaneous fission

Abstract Triple angular correlations between γ rays following spontaneous fission of 248 Cm are studied using the EUROGAM array. Results, for transitions in even-even fission-product nuclei, agree with predictions of angular correlation theory. Efficient detector systems combined with new analysis techniques offer for the first time a convenient tool to determine multipolarities of prompt γ transitions in the fission-product nuclei.

Search for octupole deformation in neutron-rich Cs nuclei

Abstract Partial level schemes of the very neutron-rich nuclei 141,143,145 Cs have been determined from the study of γ-γ-γ coincidences in 248 Cm fission fragments. Excited states of 143,145 Cs nuclei were observed for the first time. The possible existence of octupole deformation in the Cs nuclear ground states is discussed.

New excitation scheme of 139Cs

Abstract:Excited levels in 139Cs, populated in spontaneous fission of 248Cm, have been studied by means of prompt gamma spectroscopy, using the EUROGAMM 2 array. New level scheme of 139Cs, different from the one proposed recently, has been established. To confirm the new scheme, additional study of 139Cs has been performed, where γ-rays following β-decay of 139Xe to 139Cs have been measured at the mass separator OSIRIS.

High-spin states in the neutron rich fission fragments138Xe and139Xe

High-spin structures in the neutron-rich nuclei138Xe and139Xe have been investigated by observing prompt γ -rays from the spontaneous fission of248Cm with the Eurogam spectrometer. The partial level schemes were constructed on the basis of double-, triple- and quadruple-γ coincidences. The ground state band in138Xe has been extended up to 5 MeV excitation energy. The structure of the newly observed medium-spin states in139Xe is similar to the one of heavier N=85 isotones where vf72/3, vh9/2f72/2 and vf72/3 ⊗ 3− multiplets have been observed.

Search for octupole deformation in neutron-rich Xe isotopes

A search for octupole deformation in neutron-rich Xe isotopes has been conducted through prompt gammaray spectroscopy of secondary fragments produced in the spontaneous fission of248Cm. The spectrometer consisted of the Eurogam 1 array and a set of 5 LEPS detectors. Level schemes were constructed for Xe isotopes with mass number ranging from 140 to 144 and excited states for143,144Xe nuclei were observed for the first time. None of the level schemes exhibit an alternating parity quasimolecular band, a feature usually expected in nuclei in which octupole correlation effects are strong enough to produce stable octupole deformation. For several isotopes, structures observed in the level schemes are consistent with an octupole softness of the nuclei.