Spectroscopy of low-spin states in 157Dy : Search for evidence of enhanced octupole correlations

CITATION: Majola, S. N. T., et al. 2019. Spectroscopy of low-spin states in 157Dy : Search for evidence of enhanced octupole correlations. Physical Review C, 100(6):034322, doi:10.1103/PhysRevC.100.034322.The original publication is available at https://journals.aps.org/prcLow-spin states of ¹⁵⁷Dy have been studied using the JUROGAM II array, following the ¹⁵⁵Gd (α, 2n) reaction at a beam energy of 25 MeV. The level scheme of ¹⁵⁷Dy has been expanded with four new bands. Rotational structures built on the [523]5/2⁻ and [402]3/2⁺ neutron orbitals constitute new additions to the level scheme as do many of the inter- and intraband transitions. This manuscript also reports the observation of cross I⁺ →(I–1) ⁻ and I⁻ →(I–1)⁺ E1 dipole transitions interlinking structures built on the [523]5/2⁻ (band 5) and [402]3/2⁺ (band 7) neutron orbitals. These interlacing band structures are interpreted as the bands of parity doublets with simplex quantum number s=–i related to possible octupole correlations.https://journals.aps.org/prc/abstract/10.1103/PhysRevC.100.034322Publisher's versio

First candidates for γ vibrational bands built on the [505] 11/2− neutron orbital in odd-A Dy isotopes:

Rotational structures have been measured using the Jurogam II and GAMMASPHERE arrays at low spin following the 155Gd(α,2n)157Dy and 148Nd(12C,5n)155Dy reactions at 25 and 65 MeV, respectively. We report high-K bands, which are conjectured to be the first candidates of a Kπ=2+γ vibrational band, built on the [505]11/2− neutron orbital, in both odd-A155,157Dy isotopes. The coupling of the first excited K=0+ states or the so-called β vibrational bands at 661 and 676 keV in 154Dy and 156Dy to the [505]11/2− orbital, to produce a Kπ=11/2− band, was not observed in both 155Dy and 157Dy, respectively. The implication of these findings on the interpretation of the first excited 0+ states in the core nuclei 154Dy and 156Dy are also discussed

β and γ bands in N = 88 , 90, and 92 isotones investigated with a five-dimensional collective Hamiltonian based on covariant density functional theory : vibrations, shape coexistence, and superdeformation

CITATION: Majola, S. N. T. et al. 2019. β and γ bands in N=88, 90, and 92 isotones investigated with a five-dimensional collective Hamiltonian based on covariant density functional theory: Vibrations, shape coexistence, and superdeformation. Physical Review C, 100(4). doi:10.1103/PhysRevC.100.044324.The original publication is available at https://journals.aps.org/prc/A comprehensive systematic study is made for the collective β and γ bands in even-even isotopes with neutron numbers N = 88 to 92 and proton numbers Z = 62 (Sm) to 70 (Yb). Data, including excitation energies, B(E0) and B(E2) values, and branching ratios from previously published experiments are collated with new data presented for the first time in this study. The experimental data are compared to calculations using a five-dimensional collective Hamiltonian (5DCH) based on the covariant density functional theory (CDFT). A realistic potential in the quadrupole shape parameters V (β,γ ) is determined from potential energy surfaces (PES) calculated using the CDFT. The parameters of the 5DCH are fixed and contained within the CDFT. Overall, a satisfactory agreement is found between the data and the calculations. In line with the energy staggering S(I) of the levels in the 2γ + bands, the potential energy surfaces of the CDFT calculations indicate γ -soft shapes in the N = 88 nuclides, which become γ rigid for N = 90 and N = 92. The nature of the 02 + bands changes with atomic number. In the isotopes of Sm to Dy, they can be understood as β vibrations, but in the Er and Yb isotopes the 02 + bands have wave functions with large components in a triaxial superdeformed minimum. In the vicinity of 152Sm, the present calculations predict a soft potential in the β direction but do not find two coexisting minima. This is reminiscent of 152Sm exhibiting an X(5) behavior. The model also predicts that the 03 + bands are of two-phonon nature, having an energy twice that of the 02 + band. This is in contradiction with the data and implies that other excitation modes must be invoked to explain their origin.https://journals.aps.org/prc/abstract/10.1103/PhysRevC.100.044324Publisher’s versio

Low-lying positive parity bands in

The structure of the low-lying positive parity bands in 162Yb has been studied at iThemba LABS, using the 150Sm(16O,4n)162Yb fusion-evaporation reaction. A band built on the first excited $0^{+}_{2}$ state has been identified for the first time. In addition, we report new rotational levels that form the band structures of both the odd and even spin components of the $\gamma$-vibrational band. The first excited $0^{+}_{2}$ band and the even spin members of the $\gamma$-vibrational band exhibit a Landau-Zenner crossing. This crossing demonstrates that the significant signature splitting between the odd and even spin members of the $\gamma$ band is contributed to by band mixing

New collective structures in the

The 152Sm(16O, 5n)163Yb reaction at a beam energy of 93 MeV was used to study the excited states of 163Yb with the AFRODITE $\gamma$-ray spectrometer at iThemba LABS. The level scheme of 163Yb has been extended and new rotational bands established. The band based on the ground-state has been extended from a spin of 11/2- to spin 43/2-. A high-K band based on the neutron [505]11/2- Nilsson orbital has been observed and is reported for the first time in this work. Additional new states in 163Yb were observed which all decay to the yrast band. Some of these states are placed in a sequence which is conjectured to be a $\gamma$ band involving a coupling with the i 13/2[642]5/2+ neutron orbital. The band structures are discussed with reference to Cranked Shell Model (CSM) calculations and a systematic comparison with the neighbouring nuclei

First application of the Oslo method in inverse kinematics

International audienceThe $\gamma$-ray strength function ($\gamma$SF) and nuclear level density (NLD) have been extracted for the first time from inverse kinematic reactions with the Oslo method. This novel technique allows measurements of these properties across a wide range of previously inaccessible nuclei. Proton–$\gamma$ coincidence events from the $\mathrm {d}(^{86}\mathrm {Kr}, \mathrm {p}\gamma )^{87}\mathrm {Kr}$ reaction were measured at iThemba LABS and the $\gamma$SF and NLD in $^{87}\mathrm {Kr}$ was obtained. The low-energy region of the $\gamma$SF is compared to shell-model calculations, which suggest this region to be dominated by M1 strength. The $\gamma$SF and NLD are used as input parameters to Hauser–Feshbach calculations to constrain $(\mathrm {n},\gamma )$ cross sections of nuclei using the TALYS reaction code. These results are compared to $^{86}\mathrm {Kr}(n,\gamma )$ data from direct measurements

Nuclear level densities and γ\gamma-ray strength functions of 87Kr^{87}\mathrm{Kr} -- First application of the Oslo Method in inverse kinematics

The $\gamma$-ray strength function ($\gamma$SF) and nuclear level density (NLD) have been extracted for the first time from inverse kinematic reactions with the Oslo Method. This novel technique allows measurements of these properties across a wide range of previously inaccessible nuclei. Proton-$\gamma$ coincidence events from the $\mathrm{d}(^{86}\mathrm{Kr}, \mathrm{p}\gamma)^{87}\mathrm{Kr}$ reaction were measured at iThemba LABS and the $\gamma$SF and NLD in $^{87}\mathrm{Kr}$ obtained. The low-energy region of the $\gamma$SF is compared to Shell Model calculations which suggest this region to be dominated by M1 strength. The $\gamma$SF and NLD are used as input parameters to Hauser-Feshbach calculations to constrain $(\mathrm{n},\gamma)$ cross sections of nuclei using the TALYS reaction code. These results are compared to $^{86}\mathrm{Kr}(n,\gamma)$ data from direct measurements

Low- And medium-spin negative-parity bands in the Os 187 nucleus

Low- and medium-spin negative-parity bands of Os187 have been studied using the AFRican Omnipurpose Detector for Innovative Techniques and Experiments (AFRODITE) array, following the W186(He4,3n)Os187 reaction at a beam energy of 37 MeV. In the current work, all the previously known bands have been significantly extended and three new bands have been added to the level scheme. The angular distribution ratio (RAD) and polarization measurements have been used to assign spin and parity to the observed new levels. The configurations of some of the bands have been modified. The observed bands are interpreted within the cranked shell model (CSM) and cranked Nilsson-Strutinsky-Bogoliubov (CNSB) formalism. Comparison with experimental data shows good agreements. Systematic comparison with the neighboring Os185 isotope is also discussed

First candidates for γ vibrational bands built on the [505]11/2⁻ neutron orbital in odd-A Dy isotopes

Abstract Rotational structures have been measured using the Jurogam II and GAMMASPHERE arrays at low spin following the ¹⁵⁵Gd(α,2n)¹⁵⁷Dy and ¹⁴⁸Nd(¹²C,5n)¹⁵⁵Dy reactions at 25 and 65 MeV, respectively. We report high-K bands, which are conjectured to be the first candidates of a Kπ=2⁺γ vibrational band, built on the [505]11/2⁻ neutron orbital, in both odd-A155,157Dy isotopes. The coupling of the first excited K=0⁺ states or the so-called β vibrational bands at 661 and 676 keV in ¹⁵⁴Dy and ¹⁵⁶Dy to the [505]11/2− orbital, to produce a Kπ=11/2⁻ band, was not observed in both ¹⁵⁵Dy and ¹⁵⁷Dy, respectively. The implication of these findings on the interpretation of the first excited 0⁺ states in the core nuclei ¹⁵⁴Dy and ¹⁵⁶Dy are also discussed