High-spin Isomers Research Articles

Particle-hole Nature of the Light High-spin Toroidal Isomers

Nuclei under non-collective rotation with a large angular momentum above some threshold can assume a toroidal shape. In our previous work, we showed by using cranked Skyrme-Hartree-Fock approach that even-even, N=Z, high-K, toroidal isomeric states may have general occurrences for light nuclei with 28<=A<=52. We present here some additional results and systematics on the particle-hole nature of these high-spin toroidal isomers.

Competing Decay Modes of a High-spin Isomer in the Proton-unbound Nucleus $^{158}$Ta

An isomeric state at high spin and excitation energy was recently observed in the proton-unbound nucleus 158Ta. This state was observed to decay by both α and γ decay modes. The large spin change r ...

Neutron capture cross sections of 194Hg and the decays of 195Hg

The thermal cross section and resonance integral have been determined for radiative neutron capture by radioactive 194Hg by observing the γ rays emitted in the decay of 195Hg. Captures leading to the low-spin isomer of 195Hg give σ=877b and I=10,270b, while captures leading to the high-spin isomer give σ=49b and I=608b. Energies and intensities of the γ rays emitted in the decays of 195Hg produced by neutron capture have been obtained with increased precision relative to previous studies with sources produced by other reactions, leading to correspondingly improved values for β-decay branching intensities and energy levels in 195Au. New values for the half-lives of 195gHg and 195mHg are also reported.

αdecay ofAu176

The isotope $^{176}\mathrm{Au}$ has been studied in the complete fusion reaction $^{40}\mathrm{Ca}+^{141}\mathrm{Pr} \phantom{\rule{0.28em}{0ex}}\ensuremath{\rightarrow} {}^{176}\mathrm{Au}+5n$ at the velocity filter SHIP (GSI, Darmstadt). The complex fine-structure $\ensuremath{\alpha}$ decay of two isomeric states in $^{176}\mathrm{Au}$ feeding several previously unknown excited states in the daughter nucleus $^{172}\mathrm{Ir}$ is presented. An $\ensuremath{\alpha}$-decay branching ratio of ${b}_{\ensuremath{\alpha}}=9.5(11)%$ was deduced for the high-spin isomer in $^{172}\mathrm{Ir}$.

A region of high-spin toroidal isomers

The combined considerations of both the bulk liquid-drop-type behavior and the quantized angular momentum reveal that high-spin toroidal isomeric states may have general occurrences for light nuclei with 28⩽A⩽52. High-spin N=Z toroidal isomers in this mass region have been located theoretically using cranked self-consistent constraint Skyrme–Hartree–Fock model calculations.

High-spin torus isomers and their precession motions

We systematically investigate the existence of exotic torus isomers and their precession motions for a series of $N=Z$ even-even nuclei from $^{28}$Si to $^{56}$Ni. We analyze the microscopic shell structure of the torus isomer and discuss why the torus shape is generated beyond the limit of large oblate deformation. We use the cranked three-dimensional Hartree-Fock (HF) method with various Skyrme interactions in a systematic search for high-spin torus isomers. We use the three-dimensional time-dependent Hartree-Fock (TDHF) method for describing the precession motion of the torus isomer. We obtain high-spin torus isomers in $^{36}$Ar, $^{40}$Ca, $^{44}$Ti, $^{48}$Cr, and $^{52}$Fe. The emergence of the torus isomers is associated with the alignments of single-particle angular momenta, which is the same mechanism as found in $^{40}$Ca. It is found that all the obtained torus isomers execute the precession motion at least two rotational periods. The moment of inertia about a perpendicular axis, which characterizes the precession motion, is found to be close to the classical rigid-body value. The high-spin torus isomer of $^{40}$Ca is not an exceptional case. Similar torus isomers exist widely in nuclei from $^{36}$Ar to $^{52}$Fe and they execute the precession motion. The torus shape is generated beyond the limit of large oblate deformation by eliminating the $0s$ components from all the deformed single-particle wave functions to maximize their mutual overlaps.

Single-particle structures, high-spin isomers, and a strongly coupled band in odd-oddSb120

Excited states in $^{120}\mathrm{Sb}$ have been investigated using the $^{116}\mathrm{Cd}(^{7}\mathrm{Li},3n)^{120}\mathrm{Sb}$ reaction at a beam energy of 34 MeV. A total of 15 new $\ensuremath{\gamma}$ rays were added into the level scheme of $^{120}\mathrm{Sb}$. Most of the observed single-particle states can be interpreted in terms of weak coupling of the odd proton and odd neutron to an excited $^{118}\mathrm{Sn}$ core involving either vibrational states or broken neutron pairs. The previously known strongly coupled rotational band based on the $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ configuration has been extended up to the ${(15}^{\ensuremath{-}})$ state. The configuration-fixed constrained triaxial relativistic mean-field approaches and the particle rotor model are employed to discuss the high-spin isomers and strongly coupled rotational band, respectively.

Computational design of mixed-ligand adducts of Co aminovinyl ketonates with redox-active o-quinones and their derivatives

The adducts of cobalt aminovinyl ketonates with o-benzoquinones, o-benzoquinone imines, and o-benzoquinone diimines were studied by the density functional theory method (B3LYP*/6-311++G(d,p)). For all of the compounds, the ground states are low-spin structures containing a trivalent cobalt atom and a redox-active ligand in the semiquinonate form. The bulky substituents at the bis-chelate and ligand nitrogen atoms favor a decrease in the energy difference between the low-spin and high-spin isomers of the adducts containing LSCoIII and HSCoII atoms, respectively. These compounds can exhibit valence tautomerism in the crystalline state, but the relatively low stabilization energies of the high-spin isomers in solutions may induce a competing process: dissociation into the original bis-chelate and redox-active ligand.

Pure collective precession motion of a high-spin torus isomer

We investigate the precession motion of the exotic torus configuration in high-spin excited states of ${}^{40}$Ca. For this aim, we use the three-dimensional time-dependent Hartree-Fock (TDHF) method. Although the high-spin torus isomer is a unique quantum object characterized by the alignment of angular momenta of independent single-particle motions, we find that the obtained moment of inertia for rotations about an axis perpendicular to the symmetry axis is close to the rigid-body value. We also analyze the microscopic structure of the precession motion using the random-phase approximation (RPA) method for high-spin states. In the RPA calculation, the precession motion of the torus isomer is generated by coherent superposition of many one-particle--one-hole excitations across the sloping Fermi surface that strongly violates the time-reversal symmetry. By comparing results of the TDHF and the RPA calculations, we find that the precession motion obtained by the TDHF calculation is a pure collective motion well decoupled from other collective modes.

Lifetime measurements and decay spectroscopy of132I

The low-lying states of odd-odd 132 I, the 3p-3h nucleus with respect to the doubly magic 132 Sn, have been characterized from decay spectroscopy. The neutron rich Iodine and Tellurium isotopes have been produced as fission product of alpha-induced fission of 235 U and radiochemically separated. The life-time of the first excited state of 132 I have been precisely measured using LaBr3(Ce) scintillators from the decay of 132 Te. The IT decay of the high spin isomer (8 - ) in 132 I has been measured with a Low Energy Photon Spectrometer (LEPS) of segmented planar Ge detector.

Deep inelastic reactions and isomers in neutron-rich nuclei across the perimeter of the A = 180-190 deformed region

Recent results on high-spin isomers populated in deep-inelastic reactions in the transitional tungsten-osmium region are outlined with a focus on Os-190, Os-192 and Os-194. As well as the characterization of several two-quasinutron isomers, the 12(+) and 20(+) isomers in Os-192 are interpreted as manifestations of maximal rotation alignment within the neutron i(13/2) and possibly proton k(11/2) shells at oblate deformation.

Identification of new transitions feeding the high-spin isomers in139Nd and140Nd nuclei

The population of the high-spin isomers in ${}^{139}$Nd and ${}^{140}$Nd was investigated using the ${}^{96}$Zr(${}^{48}$Ca,$xn$) reaction and the JUROGAM + RITU + GREAT setup employing the recoil decay tagging technique. Three transitions feeding the 23/2${}^{+}$ isomer in ${}^{139}$Nd and two transitions feeding the 20${}^{+}$ isomer in ${}^{140}$Nd were identified. The newly observed transitions allowed the excitation energy of the isomer to be established in ${}^{139}$Nd and to assign configurations to the states and bands deexcited by the observed transitions in both nuclei.

The population of metastable states as a probe of relativistic-energy fragmentation reactions

Isomeric ratios have been measured for high-spin states in Po84198,200,206,208, At85208,209,210,211, Rn86210,211,212,213,214, Fr87208,211,212,213,214, Ra88210,211,212,214,215, and Ac89215 following the projectile fragmentation of a 1 A GeV 238U beam by a 9Be target at GSI Helmholtzzentrum für Schwerionenforschung. The fragments were separated in the fragment separator (FRS) and identified by means of energy loss and time-of-flight techniques. They were brought to rest at the centre of the RISING gamma-ray detector array and intensities of gamma rays emitted in the decay of isomeric states with half-lives between 100 ns and 40 μs and spin values up to 55/2 ℏ were used to obtain the corresponding isomeric ratios. The data are compared to theoretical isomeric ratios calculated in the framework of the abrasion–ablation model. Large experimental enhancements are obtained for high-spin isomers in comparison to expected values.

New Studies on the Aspects of Nuclear Shapes

Using the pairing-deformation-frequency self-consistent total-Routhiansurface and configuration-constrained potential-energy-surface calculations, we have studied nuclear deformation and its effect on the structure of nuclei. It was found that the high-order multipolarity-six (β6) deformation plays a significant role in superheavy nuclei. Possible non-collective highspin isomeric states which locate in the second well of actinide nuclei have been investigated with the predictions of excitation energies and configurations. High-spin isomers can extend shape coexistence in A ∼ 190 neutrondeficient nuclei. Triaxiality with γ 30 is found in the ground and excited rotational states of the A ∼ 70 germanium isotopes. Octupole correlations have also been discussed in different mass regions. In recent experiments, the textbook nucleus 158Er has been reached at ultrahigh spins around 65∼. We have studied 158Er ultrahigh-spin states by means of the self-consistent tilted-axis-cranking method based on the Nilsson shell correction and the Skyrme-Hartree-Fock model. The calculation with a ≈ 12 ° triaxialstrongly-deformed (TSD) excited configuration can well reproduce the observed large transitional quadrupole moment. It is demonstrated that the TSD minimum at negative γdeformation which appears in the principalaxis-cranking approach is a saddle point if allowing the rotational axis to change direction.

Biphenyl bridged hexadentate N6-ligands – a rigid ligand backbone for Fe(ii) spin crossover complexes

The novel hexadentate nitrogen based ligand N,N'-bis-(2-(1H-pyrazol-1-yl)pyridine-6-ylmethyl)-2,2'-biphenylenediamine (3) was synthesized and used for the preparation of iron Spin Crossover (SCO) complexes [Fe(3)][BF4]2 (4) and [Fe(3)][ClO4]2 (5), which differ only by the respective counter ion. These complex salts show different spin transition temperatures T(1/2) (135 and 157 K, respectively). This effect was studied by the investigation of the solid state structure of different low- and high-spin isomers. All complexes of this series show closely related crystal packing regardless of the counter ion, metal (Zn/Fe) and spin state. The isomer exhibiting the lower transition temperature (4) was also investigated in respect to its photomagnetic behaviour. The LIESST process could be monitored for this complex, but no reverse-LIESST was observed. The relaxation of the photo-induced state occurs at ca. 80 K, showing a complex, three-state relaxation mechanism.

Excitation of high-spin nuclear isomeric states by intermediate energy protons at the Moscow Meson Factory of the Russian Academy of Sciences’ Institute for Nuclear Research

Isomeric ratios of reaction products obtained by irradiating 197Au, 181Ta, and 93Nb targets by protons with energies of 143–325 MeV are measured via activation. The results do not agree with measurements of stopped ions [1], even though the theoretical model in [2] predicted the same mechanism for the formation of high-spin isomers in these reactions. The obtained isomeric ratios in reactions with protons of intermediate energy are 10–100 times lower than the theoretical values; consequently, the excitation mechanisms of high-spin isomers in reactions with protons and stopped ions are different.

New Geiger-Nuttall law forαdecay of heavy nuclei

Recent $\ensuremath{\alpha}$-decay data of heavy nuclei are collected and systematic analysis shows that there is a sudden change between the logarithm of decay half-life and the reciprocal of the square root of decay energy across the $N=126$ shell closure. In order to reproduce this sudden change, the new Geiger-Nuttall law is proposed where the effects of the quantum numbers of $\ensuremath{\alpha}$-core relative motion are naturally embedded in the law. The remedy achieved by a very simple parametrization of these effects is remarkable. By adding terms to the Geiger-Nuttall law, the parameters in the formula of decay half-lives need not be changed, except for some odd nuclei. This is an important development to the original Geiger-Nuttall law, which is valid for the ground-state transitions of even-even nuclei with $N\ensuremath{\ge}128$. The law is generalized to the favored and hindered transitions of the $N\ensuremath{\le}128$ nuclei and of high-spin isomers. The results of this article point to the simplicity of the underlying mechanism of the decay.

High-Kisomers in neutron-rich zirconium isotopes

The neutron-rich zirconium isotopes are a key testing ground for nuclear models due to their sensitivity to shape changes, and because they cross the $r$-process path of explosive nucleosynthesis. Furthermore, recent experimental data have revealed a high-spin isomer in ${}^{108}$Zr. Here we report the results of configuration-constrained potential-energy-surface calculations of ground states and high-$K$ states in ${}^{104--110}$Zr, restricted to quadrupole and hexadecapole shapes. These calculations enable the existing isomer data to be understood, and predictions are made for ${}^{110}$Zr.

Nickel and Palladium Complexes with New Phosphinito-Imine Ligands and Their Application as Ethylene Oligomerization Catalysts

Phosphinito-imines, a new class of P,N donors, are readily generated by reaction of bulky arylamide anions [R2CONAr]− (R2 = Me or t-Bu; Ar = 2,6-i-Pr2C6H4) with chlorophosphines ClP(R1)2. In solution, free phosphinito-imines exist in equilibrium with the corresponding amidophosphine tautomers, containing a nitrogen-bound P(R1)2 group. However, reacting the tautomer mixtures with metal precursor complexes, such as NiBr2(dme) or PdCl2(cod), selectively affords stable phosphinito-imine complexes MX2(P-N) (M = Ni, Pd) in excellent yields. These complexes are diamagnetic and exhibit square-planar structures in the solid state, but in solution, the Ni derivatives exchange with a small amount of the corresponding high-spin tetrahedral isomers. On treatment with MMAO or DEAC, NiX2(P-N) complexes become active ethylene oligomerization catalysts, affording mainly butenes along with smaller amounts of hexenes and octenes. The activity and the selectivity of these catalysts depend on the structure of the phosphinito-imine ligand and the cocatalyst used. When activated with DEAC, complexes containing the P(i-Pr)2 moiety are extremely active, achieving TOFs over 106 mol C2H4/mol Ni·h and high selectivity for butenes.

Levels in210Fr and the decay of a high-spin, multi-particle isomer

The structure of 210 Fr has been studied through the 197 Au( 18 O, 5n) 210 Fr reaction. A high-spin iso- meric state has been identified at ∼4.4 MeV. It has a lifetime of 686(17) ns and decays by twoγ-rays that are very likely to be either M2 or E3 multipolarity. The measured strengths in the case of E3 assignments are ap- proximatively 8 and 21 W.u., respectively. These would be less enhanced than is observed in the decay from the high spin isomers in 209 Fr and 211 Fr that are believed to be from a related configuration. Possible configuration assignments are discussed.