Highly-deformed Bands Research Articles

Ductile shear damage micromechanisms studied by correlative multiscale nanotomography and SEM/EBSD for a recrystallized aluminum alloy 2198 T8

The damage mechanisms of ductile fracture under shear loading of an aluminum alloy 2198T8R were studied using flat thin-sheet samples. One sample was loaded until 85% of the failure displacement and then unloaded, and another one was loaded up to failure. To overcome the inherent shortcomings of nanotomography concerning the investigation of flat samples, synchrotron nano-laminography was applied to the pre-loaded sample and provided structural information down to the nanometer scale, allowing ductile damage nucleation and evolution to be studied. The damage features, including flat cracks and intermetallic particle-related damage, were visualized in 3D from the highly-deformed shear band region. Using nano-laminography, no nano-voids were found. The damaged shear ligament was also observed after polishing via destructive correlative scanning electron microscope (SEM) and electron back-scatter diffraction (EBSD) which suggests that the detrimental flat cracks were both intergranular and transgranular. The flat cracks were related to highly-deformed bands. No nano-voids could be found using SEM analysis. Fractography on the second broken sample revealed that the flat cracks contained hardly observable nanometer-sized dimples. The final coalescence region was covered by sub-micrometer-sized dimples, inside which dispersoid particles were present. The fact that no nano-void was found for the pre-deformed sample implies that the nucleation, growth and coalescence of these sub-micrometer-sized voids occur at late stages of the loading history.

Highly deformed bands in Nd nuclei: New results and consistent interpretation within the cranked Nilsson-Strutinsky formalism

Three new highly-deformed (HD) bands are identified in Nd136 and the highly deformed band of Nd137 is extended at higher spin by four transitions, revealing a band crossing associated with the occupation of the second νi13/2 intruder orbital. Extended cranked Nilsson-Strutinsky calculations are performed for all HD bands observed in Nd134, Nd136, and Nd137, achieving for the first time a consistent interpretation of all HD bands in the Nd nuclei. The new interpretation has significant consequences, like the change of parity of the yrast HD bands of Nd134 and Nd136, and the involvement of two negative-parity neutron intruder orbitals in the configurations of most HD bands. The present experimental results and their theoretical interpretation represent an important step forward in the understanding of the second-minimum excitations in the Nd nuclei.

Characterization and analysis of deformation heterogeneities in commercial purity titanium

The effects of solute oxygen, loading direction and strain level on the microscale plastic strain distribution in representative areas of commercially-pure titanium have been characterized by correlation of high resolution SEM images captured during in situ tensile tests. A spatial organization of highly-deformed bands was observed from the early stages of plastic flow and remained nearly unchanged as the materials were strained. The high strains close to grain boundaries were related to intense local slip activity, grain boundary sliding or kink bands formation. The plastic strain field was more homogeneous in the oxygen-rich material, which was attributed primarily to a smaller contribution of grain boundary sliding, due to the presence of hard β phase particles along the grain boundaries.

Decay out of the highly deformed band inNd133

The mean lifetimes of the ${25/2}^{+}$, ${21/2}^{+}$, and ${17/2}^{+}$ states in the highly deformed (HD) band of $^{133}\mathrm{Nd}$, excited via the reaction $^{104}\mathrm{Pd}$($^{32}\mathrm{S}$,2$\mathit{pn}$)$^{133}\mathrm{Nd}$, have been measured using a recoil distance Doppler-shift method. The decay out of the HD band occurs as a result of an admixture of normally deformed (ND) components into the HD states' wave function. The consistency in the mixing amplitude was assessed from the measured lifetimes, branching ratios, and quadrupole moments of the HD and the ND bands. This analysis unequivocally confirms the earlier approach to explain the decay-out mechanism.

Nuclear Data Sheets for [formula omitted

Nuclear spectroscopic information for known nuclides of mass number 132 (Cd,In,Sn,Sb,Te,I,Xe,Cs,Ba,La, Ce,Pr,Nd,Pm,Sm,Eu) with Z = 48 to 63 and N = 84 to 69 have been evaluated and presented together with adopted energies and Jπ of levels in these nuclei. No excited state data are yet available for 132Cd. The identification of the 132Eu nuclide remains uncertain. Fairly rich structures are known in all the other A = 132 nuclides. Superdeformed structures are known in 132Pr (four SD bands and a highly-deformed structure) and in 132Nd (four SD or highly-deformed bands). Possible chiral doublet bands of π h 11 / 2 ν h 11 / 2 configuration have recently been identified in 132Pr, 132La and 132Cs. The decay scheme of 132La to 132Ba has been studied in several works, including some recent papers, but in the opinion of the evaluators, this decay scheme still suffers from incompleteness, especially from the point-of-view of separate level schemes from the ground state and the isomeric activities. The separate level schemes from two activities of 132Sb decay to 132Te are also not well established, although, the combined activity has recently been studied by the Yale group. This evaluation represents a complete update of previous evaluations of A = 132 : by Yu.V. Sergeenkov (1992Se04); and by H.R. Hiddleston and C.P. Browne (1976Hi02).

Rotational quenching of the N = 72 shell gap and the role of the intruder orbital in 132Nd

Rotational structures in 132Nd have been investigated via the 104Pd(32S,2p2n) reaction at 160 MeV. Four highly-deformed bands have been observed, out of which three have been linked to the normal-deformed states. Two of them are signature partners. A mixing at high spin is observed between levels of one highly-deformed band and the ground-state band allowing for an unambiguous assignment of the spins and parity of that band. The present data brings new evidence on the role of the N = 72 shell gap to the stabilization of the highly-deformed minimum in the A = 130 mass region and on the importance of the νi132 intruder orbital in the structure of the highly-deformed bands.

Decay out of the highly deformed bands in the N = 75 isotones 137Sm and 139Gd

Transitions linking the highly deformed (HD) bands to states of normal deformation in 137Sm and 139Gd have been identified in experiments performed at GASP. The spins deduced for the HD bands in these N = 75 isotones support the previously assigned νi 13 2 [660] 1 2 + configuration. The different decay-out patterns of the two otherwise similar HD bands are tentatively explained by the difference in pairing between the Z = 62 and Z = 64 proton systems.

Superdeformation around 144Gd

The study of superdeformation in nuclei around the nucleus 144Gd, which can be considered as doubly-closed at superdeformed shape, provided detailed knowledge about the structure of superdeformed bands in this region. The chain of Gd isotopes showing superdeformation could be extended to 143Gd. Since highly-deformed bands are known in 139,141Gd, it appears that the transition between the regions of superdeformed nuclei with A ≈ 150 and of highly-deformed nuclei with A ≈ 130 is rather sharp and takes place around N = 78 as theoretically predicted. In 144Gd four excited superdeformed bands have been found in addition to the yrast superdeformed band. They form two pairs of signature partner bands of π6 1 π[404]9 2ν7 0 and π6 1 π[411]3 2ν7 0 configurations. In 145Gd for the first time two crossings have been observed in a superdeformed band, which are assigned to the alignment of an i 13 2 proton pair and a subsequent crossing of the i 13 2 [642]5 2 and i 11 2 [651]1 2 neutron orbitals, respectively.

Shape change along the highly-deformed band in 137Nd

Lifetimes of states of the highly-deformed (HD) band in 137Nd have been measured using the Doppler shift attenuation method. A line-shape analysis has been carried out for individual states, resulting in transition quadrupole moments which decrease with increasing spin. This represents the first confirmation of previous total routhian surface (TRS) calculations that predicted a drift towards positive γ values of the HD minimum (at essentially constant β deformation). The lifetime data show a rather modest deformation of the HD band structure, indicating a softening of the nuclear potential at HD shape.

Decay Out of the Yrast and Excited Highly Deformed Bands in the Even-Even Nucleus 134Nd.

The decay out of the yrast and excited highly deformed (HD) bands in ${}^{134}$Nd has been investigated via the ${}^{28}\mathrm{Si}{+}^{110}\mathrm{Pd}$ reaction at 130 MeV using the GASP array. Several deexcitation pathways have been established for both the yrast and excited HD bands. The resulting spins remove previous ambiguities in the assignment of the excited HD band and confirm the structure assigned to the yrast HD band. The decay out is understood in terms of mixing between the normal-deformed and HD states, which is triggered by the crossing between the $\ensuremath{\nu}{i}_{13/2}$ and $\ensuremath{\nu}{d}_{5/2}$ orbitals.

Competing mechanism for generating high spin excitations in γ-soft nuclei: the 136Nd case

High-spin structures in 136Nd have been investigated via the 110Pd( 30Si,4n) reaction at 125 MeV using the GASP array. Several bands consisting of stretched quadrupole transitions were identified. Two of them reach spins comparable to those of the highly-deformed (HD) band in 136Nd, which is based on a neutron i 13 2 - h 9 2 f 7 2 configuration. Total routhian surface (TRS) calculations indicate that regular high-spin excitations in this γ-soft nucleus, can be also generated through successive pairs of h 11 2 protons and neutrons coupled to a stable small-deformation triaxial core. The previously reported γ-ray transitions of an excited HD band, identical to the yrast HD band, are not confirmed by our data.

Decay out of the highly deformed bands in the odd Nd isotopes: The 137Nd nucleus.

The decay of the highly deformed (HD) band in the nucleus {sup 137}Nd has been studied with the GASP array using the reactions {sup 110}Pd+{sup 30}Si and {sup 123}Sb+{sup 19}F. Four decay paths linking the HD band to the normal-deformed states have been established, which fix {ital I}{sup {pi}}=29/2{sup +} for the lowest state of the HD band lying at {ital E}{sub {ital x}}=4885 keV. The sudden disappearance, at the low spin side, of the HD bands in the {sup 133,135,137}Nd isotopes can be explained by total Routhian surface calculations through a change of the nuclear shape which is microscopically related to the transfer of the valence neutron from a {ital N}=6 to a {ital N}=4 Nilsson orbital.

The role of nuclear dynamics in the population of highly- and super-deformed bands

The population of the highly-deformed band in 133Nd has been studied using the reactions 32S + 105Pd and 60Ni + 77Se to form the compound nucleus 137Sm at comparable excitation energy. Experimental results do not show any dependence on the entrance-channel mass asymmetry, in agreement with recent results for 135Nd and at variance with those for the 147,148Gd and 152Dy nuclei. The experimental data on the entrance-channel dependence of the population of highly- and super-deformed bands in the mass regions A ˜130,150and190 are discussed in terms of dynamical effects which occur during the formation process of the compound nucleus as well as in the fission channel.

Multiple-highly deformed bands in the nucleus 134Nd

A high statistics experiment has been performed at the GASP detector array employing the 110Pd + 28Si reaction at 130 MeV to populate 134Nd. Our findings do not confirm earlier data on the highly-deformed band of this nucleus. On the other hand, two new rotational sequences have been identified which show the characteristics of the intruder bands in the A = 130 mass region. This is one of the first results indicating the presence of excited highly-deformed bands in nuclei of this region. The behaviour of the dynamical moment of inertia of one of the bands is quite different from that of the highly-deformed bands previously known.

Population effects in the highly-deformed bands of 131Ce and 135Nd from 18,16O-induced reactions

The highly-deformed bands in 131Ce and 135Nd have been studied with 18O and 16O projectiles, respectively. Compared to heavy-ion reactions, the amount of sidefeeding increases in 131Ce but not in 135Nd This suggests 135Nd is insensitive to the maximum angular momentum brought in. The Doppler Shift Attenuation Method was used to extract a value for the highly-deformed quadrupole moment in 131Ce of Q 0 = 5.5 ± 0.5 eb. It is concluded that the increased sidefeeding has little effect on the measured Q 0.