Search

Excited states in the 134Sb nucleus, populated in the β−-decay of 134Sn, have been studied at the mass separator OSIRIS. The 134Sn activity was produced via fast neutron-induced fission of 238U target. A main result was the discovery of a very low-lying first-excited state of 134Sb, at 13 keV, which has led to a strong revision of the level scheme. The new results are compared with different theoretical calculations and with the known data for the analogous neutron and proton two-particle nucleus in the 208Pb region. On the basis of this comparison, the energy of the (πg 7/2νf 7/2)7− isomer is estimated to be about 250 keV, some 100 keV lower than previously reported.

The 137I nucleus, populated in the spontaneous fission of 248Cm has been studied by means of prompt γ-ray spectroscopy using the EUROGAM2 array. Medium-spin yrast excitations in 137I were observed for the first time. The experimental level scheme is compared to the shell model calculation with modified Kuo-Herling interaction. The theoretical predictions differ significantly from the experimental results, indicating that the excitation pattern in 137I deviates significantly from the shell model scheme.

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.

Neutron-rich, 88-94Kr nuclei, populated in spontaneous fission of 248Cm, have been studied with EUROGAM 2, by measuring prompt γ-rays. Many new excited states in even-even Kr isotopes have been identified. For the first time spins and parities were determined experimentally in these nuclei. Our results indicate that the quadrupole deformation of Kr isotopes will appear only above N = 58, as observed in Sr and Zr nuclei. The newly found 3- level at 1506.4 keV in 90Kr suggests the exsistence of a new region of increased octupole correlations, probably associated with the ν(d 5/2 h 11/2) pair of Δl = Δj = 3 orbitals.

The very neutron-rich nucleus 138Te produced in the spontaneous fission of 248Cm has been investigated using the EUROGAM II γ-ray multidetector array. The excited states of 138Te observed for the first time indicate that the region of ground state deformation beyond the doubly magic nucleus 132Sn has yet not been reached.

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.

Neutron-rich, N=84 nuclei from the 132Sn region, populated in spontaneous fission of 248Cm, have been studied with EUROGAM 2. Excited states and their spins and parities in the 136Te nucleus were established up to 17ħ. OXBASH code calculations support the experimental identification of maximum aligned configurations in 136Te. Empirical shell model calculations for the Iπ= 14+ level in 136Te indicate that the adopted mass of the 134Te nucleus should be lowered by 200(80) keV.

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.

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.

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.

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.

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.

The Eurogam-1 array has been used to study $\ensuremath{\gamma}$ rays emitted following the spontaneous fission of a $^{248}\mathrm{Cm}$ source. Yrast level schemes for the neutron-rich nuclei $^{152,154,156}\mathrm{Nd}$ have been constructed. The stopping of the Nd fragments in the source material leads to Doppler-broadened line shapes for those states that have lifetimes comparable to the stopping time. This paper describes the first measurements of lifetimes of medium-spin states in very neutron-rich nuclei obtained from the analysis of these line shapes. The transition quadrupole moments for the yrast states in the spin range $(10\ensuremath{-}16)\ensuremath{\hbar}$ have been deduced to be 5.88 \ifmmode\pm\else\textpm\fi{} 0.08 e b ($^{152}\mathrm{Nd}$), 5.75 \ifmmode\pm\else\textpm\fi{} 0.10 e b ($^{154}\mathrm{Nd}$), and 5.33 \ifmmode\pm\else\textpm\fi{} 0.16 e b ($^{156}\mathrm{Nd}$).

The limiting conductivity of Dy3+(aq) has been determined for the first time by linear extrapolation of conductivity measured in dilute aqueous solutions of (DyCl3+HCl) at 25°C as λo(Dy3+, aq) = (62.9±0.7) S-cm2-eq-1. A second set of conductivity measurements in dilute aqueous solutions of DyCl3 has given evidence of very slight hydrolysis of the cation, with a first hydrolysis constant of 6 x 10−8 mol-dm−3 (pK=7.2±0.5) calculated by applying the Onsager-Kim law of electrolyte mixtures.