High-spin Isomers Research Articles

Two-neutron and core-excited states in Pb210 : Tracing E3 collectivity and evidence for a new β -decaying isomer in Tl210

Yrast and near-yrast levels up to an I=17ℏ spin value and a 6-MeV excitation energy have been delineated in the “two-neutron” 210Pb nucleus following deep-inelastic reactions involving 208Pb targets and a number of heavy-ion beams at energies ∼25% above the Coulomb barrier. The level scheme was established on the basis of multifold prompt and delayed coincidence relationships measured with the Gammasphere array. In addition to the previously known states, many new levels were identified. For most of the strongly populated states, spin-parity assignments are proposed on the basis of angular distributions. The reinvestigation of the ν(g9/2)2, 8+ isomeric decay results in the firm identification of the low-energy E2 transitions involved in the 8+→6+→4+ cascade, and in a revised 6+ level half-life of 92(10) ns, nearly a factor of 2 longer than previously measured. Among the newly identified states figure spin I=4–10ℏ levels associated with the νg9/2i11/2 multiplet, as well as yrast states involving νg9/2j15/2, νi11/2j15/2, and ν(j15/2)2 neutron couplings. The highest-spin excitations are understood as 1p−1h core excitations and the yrast population is found to be fragmented to the extent that levels of spin higher than I=17ℏ could not be reached. Four E3 transitions are present in the 210Pb yrast decay; three of these involve the g9/2→j15/2 octupole component, as reflected in the 21(2) and >10 Weisskopf unit enhancements of the B(E3) rates of the first two. The fourth, 16+→13−E3 transition corresponds to the 3− core octupole excitation built on the νi11/2j15/2 state, in analogy to a similar E3 coupling to the νj15/2 level in 209Pb. Shell-model calculations performed for two-neutron states and 1p−1h 208Pb core excitations are in good agreement with the data. Evidence was found for the existence of a hitherto unknown high-spin β-decaying isomer in 210Tl. Shell-model calculations of the 210Tl levels suggest the possibility of a 11+ long-lived, β-decaying state, and the delayed yields observed in various reactions fit rather well with a 210Tl assignment.

Fine structure in the α decay of high-spin isomers in Lu155 and Hf156

Fine structure in the α decay of high-spin isomers in Lu155(25/2−) and Hf156(8+) has been studied for the first time using αγ-coincidence analysis. Three new α decays from Lu155(25/2−) and two from Hf156(8+) have been identified, populating seniority s>1 states in the N=82 nuclei Tm151 and Yb152, respectively. The reduced hindrance factors of the α decays support the previous configuration assignments of the populated states. This is the first observation of states with excitation energy greater than 1.5 MeV being populated following α decay in nuclei outside of the Pb208 region.Received 4 July 2018DOI:https://doi.org/10.1103/PhysRevC.98.024321©2018 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAlpha decayEnergy levels & level densitiesIsomer decaysLifetimes & widthsNuclear spin & parityShell modelNuclear Physics

Gamow-Teller transitions from high-spin isomers in N=Z nuclei

Gamow-Teller (GT) transitions from high-spin isomers are studied using the sum-rule approach and the shell model. The GT transition strengths from the high-spin isomeric states show a stronger collectivity than those from the ground states in two $N=Z$ nuclei, $^{52}$Fe and $^{94}$Ag. It is argued that the spin-up and spin-down Fermi spheres involved in the GT transitions from the high-spin isomeric states play important roles. These Fermi spheres are analogous to the isospin-up and isospin-down Fermi spheres for the GT transitions from the ground states in $N>Z$ nuclei and create a strong collectivity.

Occurrence of a chiral-like pair band and a six-nucleon noncollective oblate isomer in 120I

We report for the first time two distinctive features in the odd–odd nucleus 120I: a pair of doublet bands and a high-spin isomer built on the πh11/2νh11/2 configuration. For producing the excited states of 120I, a fusion-evaporation reaction 118Sn(6Li, 4n) at E=lab48 MeV was employed. The beam was provided by the 14UD tandem accelerator of the Heavy Ion Accelerator Facility at the Australian National University. The observed doublet structure built on the positive-parity states is the first case and unique in isotopes with Z=53. The emerging properties are indicative of the known chiral characteristics, leading to a doubling of states for the πh11/2νh11/2 configuration. In contrast, the high-spin isomer with a half-life of 49(2) ns at spin-parity Jπ=25+ can be explained in terms of a noncollective oblate structure with the full alignment of six valence nucleons outside the 114Sn core: three protons (g7/2)1(d5/2)1(h11/2)1 and three neutrons (h11/2)3. This is an outstanding case that reveals a pure single-particle structure consisting of equal numbers of valence protons and neutrons outside the semi-double shell closure of 114Sn with Z=50 and N=64.

Properties of Superheavy Isotopes $Z=120$ and Isotones $N=184$ Within the Skyrme--HFB Model

We study the nuclear properties of even-even superheavy $Z$=120 isotopes and $N$=184 isotones with the Skyrme Hartree-Fock-Bogoliubov (HFB)approach. Within this model we examine the deformation energy surfaces and two paths to fission: a reflection-symmetric path with elongated fission fragments (sEF) and a reflection-asymmetric path corresponding to elongated fission fragments (aEF). Furthermore, we explore the energy surfaces in the region of very large oblate deformations with toroidal nuclear density distributions. While the energy surfaces of toroidal $Z$=120 isotopes and $N$=184 isotones do not possess energy minima without angular momenta,local energy minima (toroidal high spin isomeric states) appear for many of these superheavy nuclei with specific angular momenta about the symmetry axis. We have theoretically located the toroidal high spin isomers (THSIs) of $^{302}$Og$_{184}$,$^{302}120_{182}$, $^{306}120_{186}$, and $^{306}122_{184}$.

Measurements and analysis of [formula omitted]Hf production cross sections under [formula omitted]Ta and [formula omitted]W irradiation by protons with 0.04–2.6 GeV energies

This paper presents the results of experimental determination and computational simulation of the independent cross sections of 178m2Hf production in natTa and natW thin targets irradiated by mono-energetic proton beams in the energy range from ∼0.04 up to 2.6 GeV. The cross sections were determined using the γ-spectrometry technique without chemical separation of irradiated samples. The obtained experimental results were compared with the results of simulations based on the modified CEM03.03-ext intranuclear cascade model, which allows to analyze both the cross sections of residual nuclei production and the probabilities of long-lived isomeric states formation. Verification of the isomeric yield calculation model was demonstrated based on experimental data on high-spin isomer production cross sections in 208Pb target irradiated by protons.

New decay modes of the high-spin isomer of 124Cs

A new $\beta^{+}$ /EC branch of $0.11\pm 0.02$ % from the $(7)^{+}$ isomer of 124Cs was identified in a measurement of the decay of 124Cs using the $8\pi$ spectrometer at TRIUMF. Combinations of $\gamma$ - $\gamma$ , $\gamma$ - $e^{-}$ , and $e^{-}$ - $e^{-}$ coincidence data were used to further investigate the isomeric decay. Six new transitions were observed and their branching ratios were measured.

Observation of a γ-decaying millisecond isomeric state in 128Cd80

A new high-spin isomer in the neutron-rich nucleus 128Cd was populated in the projectile fission of a 238U beam at the Radioactive Isotope Beam Factory at RIKEN. A half-life of T1/2=6.3(8) ms was measured for the new state which was tentatively assigned a spin/parity of (15−). The experimental results are compared to shell model calculations performed using state-of-the-art realistic effective interactions and to the neighbouring nucleus 129Cd. In the present experiment no evidence was found for the decay of a 18+E6 spin-trap isomer, based on the complete alignment of the two-neutron and two-proton holes in the 0h11/2 and the 0g9/2 orbit, respectively, which is predicted to exist by the shell model.

Toroidal high-spin isomers in the nucleus 120304

Strongly deformed oblate superheavy nuclei form an intriguing region where the toroidal nuclear structures may bifurcate from the oblate spheroidal shape. The bifurcation may be facilitated when the nucleus is endowed with a large angular moment about the symmetry axis with $I=I_{z}$. The toroidal high-$K$ isomeric states at their local energy minima can be theoretically predicted using the cranked self-consistent Skyrme-Hartree-Fock method. We use the cranked Skyrme-Hartree-Fock method to predict the properties of the toroidal high-spin isomers in the superheavy nucleus $^{304}{120}_{184}$.

Quantum chemical modeling of valence tautomeric adducts of CoII bischelates with pyrene-4,5-diimines

Quantum chemical study of mixed-ligand (1: 1) adducts of tetracoordinated cobalt complexes (diketonates, bis-aminovinylketonates, and bis-salicylaldiminates) with pyrene-4,5-diimines using density functional theory (DFT B3LYP*/6-311++G(d,p)) revealed compounds possessing valence tautomeric properties. The mechanisms of intramolecular electron transfer accompanied by changing magnetic properties of the complexes under consideration were studied. It was shown that the variation of substituents at the nitrogen atoms of the diimine ligand and the donor groups in the cobalt bischelate, as well as the annulation of five- and six-membered rings to the azomethine fragment exerts a considerable influence on the stability of the formed adducts and the energy difference between their low- and high-spin isomers.

Nuclear inelastic scattering and density functional theory studies of a one-dimensional spin crossover [Fe(1,2,4-triazole)2(1,2,4-triazolato)](BF4) molecular chain

Nuclear inelastic scattering (NIS) experiments have been performed in order to study the vibrational dynamics of the low- and high-spin states of the polynuclear 1D spin crossover compound [Fe(1,2,4-triazole)2(1,2,4-triazolato)](BF4) (1). Density functional theory (DFT) calculations using the functional B3LYP* and the basis set CEP-31G for heptameric and nonameric models of the compound yielded the normal vibrations and electronic energies for high-spin and low-spin isomers of three models differing in the distribution of anionic trz- ligands and BF4- anions. On the basis of the obtained energies a structural model with a centrosymmetric Fe(trzH)4(trz-)2 coordination core of the mononuclear unit of the chain is proposed. The obtained distribution of the BF4- counteranions in the proposed structure is similar to that obtained on the basis of X-ray powder diffraction studies by Grossjean et al. (Eur. J. Inorg. Chem., 2013, 796). The NIS data of the system diluted to 10% Fe(ii) content in a 90% Zn(ii) matrix (compound (2)) show a characteristic change of the spectral pattern of the low-spin centres, compared to the low-spin phase of the parent Fe(ii) complex (1). DFT calculations reveal that this is caused by a change of the structure of the neighbours of the low-spin centres. The spectral pattern of the high-spin centres in (2) is within a good approximation identical to that of the high-spin Fe(ii) isomer of (1). The inspection of the molecular orbitals of the monomeric model systems of [Fe(trzH)4(trz-)2] and [Fe(trzH)6], together with calculations of spin transition energies, point towards the importance of an electrostatic effect caused by the negatively charged ligands. This results in the stabilisation of the low-spin state of the complex containing the anionic ligand and shortening of the Fe-N(trz-) compared to the Fe-N(trzH) bond in high-spin, but not in low-spin [Fe(trzH)4(trz-)2].

Spectroscopy and high-spin structure ofFr210: Isomerism and potential evidence for configuration mixing

The structure of Fr-210 has been established up to an excitation energy of similar to 5.5 MeV and spins of similar to 25h, via time-correlated gamma-ray spectroscopy and using the Au-197(O-18, 5n)Fr-210 reaction with pulsed beams at an energy of 97 MeV. A significantly different level scheme has been obtained compared to previous publications. Several isomers are reported here, including a J(pi) = (23)(+), tau = 686(9)-ns state at 4417 keV and a 10(-), 29.8(11)-ns state at 1113 keV. The former isomer has been associated with the pi(h(9/2)(3)i(13/2)(2))v(p(1/2)(-2)f(5/2)(-1)) configuration and decays via proposed E3 transitions with strengths of 8.4(3) and 21.2(8) W.u. There are only very few known cases of a high-spin isomer decaying via two parallel E3 transitions. Indeed, this is not seen in other Fr nuclei, and consequently these strengths differ from related decays in the neighboring isotopes. However, by examining the systematics of E3 transitions in trans-lead nuclei, we suggest that the weaker of the two transitions decays to a mixed 20-state. Systematics of the 10-isomer are also discussed. Comparisons are made between the observed spectrum of states and those predicted from semiempirical shell-model calculations.

Nuclear inelastic scattering study of a dinuclear iron(II) complex showing a direct spin transition

The results of the nuclear inelastic scattering (NIS)/nuclear resonance vibrational spectroscopy (NRVS) for the powder spectra of dimeric [Fe 2 L 5(NCS) 4] (L = N-salicylidene-4-amino-1,2,4-triazole) complex are presented. This system is spin crossover (SCO) material tagged with a fluorophore that can sense or “feel” the SCO signal ripping through the molecular network and thereby providing an opportunity to register the SCO transition. The spectra have been measured for the low-spin and high-spin phases of the complex. The high-spin isomer reveals one broad band above 200 cm −1, while the low-spin one displays two intense bands in the range from 390 to 430 cm −1, accompanied by a number of weaker bands below this area and one at ca. 490 cm −1. A normal coordinate analysis based on density functional calculations yields the assignment of the spin marker bands to particular molecular modes. In addition the vibrational contribution to the spin transition has been estimated

Theoretical studies of possible toroidal high-spin isomers in the light-mass region

We review our theoretical knowledge of possible toroidal high-spin isomers in the light mass region in 28$\le$$A$$\le$52 obtained previously in cranked Skyrme-Hartree-Fock calculations. We report additional toroidal high-spin isomers in $^{56}$Ni with $I$=114$\hbar$ and 140$\hbar$, which follow the same (multi-particle)--(multi-hole) systematics as other toroidal high-spin isomers. We examine the production of these exotic nuclei by fusion of various projectiles on $^{20}$Ne or $^{28}$Si as an active target in time-projection-chamber (TCP) experiments.

Odd tensor electric transitions in high-spin Sn-isomers and generalized seniority

The similar behavior of the B(E1) values of the recently observed 13− odd tensor E1 isomers and the B(E2) values of the 10+ and 15− even tensor E2 isomers in the Sn-isotopes has been understood in terms of the generalized seniority for multi-j orbits by using the quasi-spin scheme. This simple approach proves to be quite successful in explaining the measured transition probabilities and the corresponding half-lives in the high-spin isomers of the semi-magic Sn-isotopes. Hence, we show for the first time the occurrence of seniority isomers in the 13− Sn-isomers, which decay by odd-tensor E1 transitions to the same seniority states.

A new high-spin isomer in 195Bi

A new high-spin isomer has been identified in 195Bi at the focal plane of the HYbrid Recoil mass Analyser (HYRA) used in the gas-filled mode. The fusion evaporation reactions 169Tm (30Si, x n) 193, 195Bi were used with the beam energies on targets of 168 and 146MeV for 6n and 4n channels, respectively. The evaporation residues, separated from the fission fragments, and their decays were detected at the focal plane of HYRA using MWPC, Si-Pad and clover HPGe detectors. The half-life of the new isomer in 195Bi has been measured to be 1.6(1)μs. The configuration of the new isomer has been proposed and compared with the other isomers in this region. The Total Routhian Surface (TRS) calculations for the three-quasiparticle configurations corresponding to the new isomer suggest an oblate deformation for this isomeric state. The same calculations for different configurations in 195Bi and for the even-even 194Pb core indicate that the proton i 13/2 orbital has a large shape driving effect towards oblate shape in these nuclei.

Toroidal high-spin isomers in light nuclei with N ≠ Z

The combined considerations of both the bulk liquid-drop-type behavior and the quantized aligned rotation with cranked Skyrme–Hartree–Fock approach revealed previously (Staszczak and Wong 2014 Phys. Lett. B 738 401) that even–even, N = Z, toroidal high-spin isomeric states have general occurrences for light nuclei with . We find that in this mass region there are in addition toroidal high-spin isomers when the single-particle shells for neutrons and protons occur at the same cranked frequency Examples of toroidal high-spin isomers, S20(I = 74ℏ) and Ar22(I = 80,102ℏ), are located and examined. The systematic properties of these toroidal high-spin isomers fall into the same regular (multi-particle)-(multi-hole) patterns as other N = Z toroidal high-spin isomers.

High-spin yrast structure ofHg204from the decay of a four-hole,22+isomer

A high-spin isomer with $\ensuremath{\tau}g700$ ns has been found in $^{204}\mathrm{Hg}$, populated in reactions of 1360-MeV $^{208}\mathrm{Pb}$ and 330-MeV $^{48}\mathrm{Ca}$ beams with a thick $^{238}\mathrm{U}$ target and a 1450-MeV $^{208}\mathrm{Pb}$ beam on a thick $^{208}\mathrm{Pb}$ target. The observed $\ensuremath{\gamma}$-ray decay of the isomer has established the yrast states below it, including another isomer with $\ensuremath{\tau}=33(3)$ ns. The experimental results are compared with shell-model calculations that include four holes in the configuration space between $^{132}\mathrm{Sn}$ and $^{208}\mathrm{Pb}$. The available spectroscopic information, including transition strengths, total conversion, and angular correlation coefficients, together with the observed agreement with the calculations, allows spin, parity, and configuration assignments to be proposed for the experimental states. The $\ensuremath{\tau}g700$ ns isomer is the ${22}^{+}$ state of maximum spin available from the alignment of the four valence holes with the configuration $\ensuremath{\pi}{h}_{11/2}^{\ensuremath{-}2}\ensuremath{\nu}{i}_{13/2}^{\ensuremath{-}2}$.

The Study of Isomeric Ratios in Photonuclear Reactions Forming High Spin Isomers in the Giant Dipole Resonance Region

We studied the isomeric ratios in odd-odd nuclei \(^{196}\)Au,\(^{182}\)Ta and \(^{194}\)Ir with high spin isomeric states produced in \(^{197}\)Au\((\gamma, n)\) \(^{196m,g}\)Au, \(^{183}\)W\((\gamma, p)\) \(^{182m,g}\)Ta and \(^{185}\)Pt\((\gamma, p)\)\(^{194m,g}\)Ir reactions by using the activation technique and \(\gamma\)-ray spectroscopic method in the giant dipole resonance (GDR) region. The high-purity natural Au, W and Pt foils in disc shape were irradiated with bremsstrahlungs generated from an electron accelerator Microtron. The irradiated foils were measured by the high resolution \(\gamma\)-ray spectroscopic system which consists of a Ge(HP) detector and a multichannel analyzer. In order to improve the accuracy of the experimental results, necessary corrections were made in the \(\gamma\)-ray activity measurements and data analysis. The results were analyzed, discussed and compared with those of other authors as well as with theoretical model calculations. The study shows that the isomeric ratios in nuclei with high spin isomeric states are much lower than that in low spin isomeric state isomers.

Spectroscopy of the Low-lying States Near the High Spin Isomer in $^{108}$Ag

A comprehensive study of the low-lying states of 108Ag, near the isomeric state at E i = 110 keV with Jπ = 6+ and T 1/2 = 438 y, has been presented. Spectroscopy of these states has been carried out using the reaction 100Mo(11B, 3nγ)108Ag at 39 MeV beam energy using INGA. The multipolarities and electromagnetic nature of the transitions have been assigned based on the angular correlation and polarization measurements. The experimentally identified states have been compared to the results of the Projected Hartree-Fock calculations to understand the configurations involved in these states.