High-spin Isomers Research Articles

Vibrational spectrum of the spin crossover complex [Fe(phen)2(NCS)2] studied by IR and Raman spectroscopy, nuclear inelastic scattering and DFT calculations

The vibrational modes of the low-spin and high-spin isomers of the spin crossover complex [Fe(phen)(2)(NCS)(2)] (phen = 1,10-phenanthroline) have been measured by IR and Raman spectroscopy and by nuclear inelastic scattering. The vibrational frequencies and normal modes and the IR and Raman intensities have been calculated by density functional methods. The vibrational entropy difference between the two isomers, DeltaS(vib), which is--together with the electronic entropy difference DeltaS(el)--the driving force for the spin-transition, has been determined from the measured and from the calculated frequencies. The calculated difference (DeltaS(vib) = 57-70 J mol(-1) K(-1), depending on the method) is in qualitative agreement with experimental values (20-36 J mol(-1) K(-1)). Only the low energy vibrational modes (20% of the 147 modes of the free molecule) contribute to the entropy difference and about three quarters of the vibrational entropy difference are due to the 15 modes of the central FeN(6) octahedron.

Pairing correlations in high-spin isomers

High-spin isomers with ${J}^{\ensuremath{\pi}}=49/{2}^{+}$ and ${27}^{+}$ have been systematically observed in a number of $N=83$ isotones with $60\ensuremath{\le}Z\ensuremath{\le}67$ at excitation energies ~9 MeV. Based on experimental excitation energies, an odd-even binding energy staggering has been extracted for the first time for these multi-quasiparticle states. Surprisingly, the magnitude of the odd-even effect in high-spin isomers turned out to be very close to that in ground states, thus challenging conventional wisdom that pairing correlations are reduced in highly excited states. Theoretical analysis based on mean-field theory explains the observed proton number dependence of the odd-even effect as a manifestation of strong pairing correlations in the highly excited states. Mean-field effects and the proton-neutron residual interaction on the odd-even staggering are also examined.

Measurement of the g-Factor of the 27− High-Spin Isomer State of 152Dy

The g-factor of the 27− isomer state of 152Dy has been measured using the Time- Integral Perturbed Angular Distribution (TIPAD) method. The high-spin states of 152Dy have been populated by 141Pr(16O,p4n)152Dy reaction at E = 115 MeV from the AVF cyclotron at CYRIC. The paramagnetic correction factor of Dy ions in Pr has been determined to be 4.2(5) by the Time- Differential Perturbed Angular Distribution (TDPAD) measurement of the 21− state of 152Dy. As a result, the g-factor of the 27− isomer state of 152Dy has been obtained to be +0.09(5). This shows the smaller value than the expected one of +0.39 deduced from a fully aligned configuration of π(h 11 2/2 ) ⊗ v(f 7 2/2 h 9/2 i 13/2).

Nuclear g factors and structure of high-spin isomers in 190,192,194Pt and 196,198Hg

The integral perturbed angular distribution (IPAD) method in an external magnetic field has been used to measure the g factors of isomers in the 190,192,194Pt and 196,198Hg nuclei, populated in the ( α , 2 n )-reaction. The results are as follows: 190Pt, g ( 12 + ) = − 0.17 ( 12 ) , g ( 10 − ) = − 0.0016 ( 36 ) , g ( 7 − ) = + 0.62 ( 9 ) ; 192Pt, g ( 12 + ) = − 0.18 ( 9 ) , g ( 10 − ) = − 0.0012 ( 10 ) , g ( 7 − ) = 0.48 ( 12 ) ; 194Pt, g ( 12 + , new assignment ) = − 0.17 ( 7 ) , g ( 7 − ) = + 0.26 ( 8 ) ; 196Hg, g ( 12 + and 10 + ) = − 0.19 ( 6 ) , g ( 7 − ) = − 0.030 ( 17 ) ; 198Hg, g ( 12 + and 10 + ) = − 0.18 ( 8 ) , g ( 7 − ) = − 0.033 ( 14 ) . The intrinsic structure of the isomers is discussed. The 12 + states have the rotational-aligned ( ν i 13 / 2 −2 ) structure. The missing rotation-aligned ( ν i 13 / 2 −2 ) 12 + state is suggested to be isomeric in 194Pt (instead of the 10 + state) and to which the g = − 0.17 ( 6 ) value has to be attributed. From the g factors of the 10 − states in 190Pt and 192Pt, which have the configuration ν 9 / 2 − [ 505 ] ⊗ ν 11 / 2 + [ 615 ] , the anomalous g l -factor for neutrons has been derived as δ g l = − 0.028 ( 6 ) . The trend from negative g factors of the 7 − states in the 196,198Hg nuclei to positive values for the corresponding states in the 190,192,194Pt nuclei indicates a change in the intrinsic structure of the lowest negative-parity bands, from mainly ( ν i 13 / 2 −2 ) in Hg to mainly ( π h 11 / 2 −2 ) in Pt.

Particle-core coupling in the transitional proton emitters 145, 146, 147Tm

Excited states in 3 transitional proton emitters 145,146,147Tm were studied using the Gammasphere Ge array coupled with the Argonne Fragment Mass Analyzer. The 147Tm level scheme was extended and the unfavored signature partner of the decoupled proton h 11/2 band was found. A rotational band feeding the high-spin isomer in 146Tm was observed with properties similar to the 147Tm ground-state band. A regular sequence of γ rays correlated with the ground-state 145Tm proton decay has properties of the h 11/2 band as well. In addition, coincidences between the fine structure proton line and the 2+ → 0+ γ-ray transition in the daughter nucleus were detected. Comparison between level energies measured and calculated using the Particle Rotor model indicates that 145Tm might be γ-soft.

High-spin shape isomers and the nuclear Jahn-Teller effect

High-spin isomers were systematically studied in N = 83 isotones. These isomers are of stretch coupled configurations and have oblate shapes. High-spin isomers can be categorized to be high-spin shape isomer, as they are caused by the sudden shape change from near spherical to an oblate shape. These isomers are considered to be a good example of the nuclear Jahn-Teller effect. By the systematic study of high-spin isomers, several results were obtained, such as (1) change of Z = 64 sub-shell gap energy and (2) experimental pairing gap energy at high-spin states. The Z = 64 sub-shell gap energy was found to decrease from 2.4 to 1.9 MeV as the proton number decreases from 64 to 60. Paring gap energies of high-spin states were experimentally extracted by the three-point expression using binding energies and excitation energies of high-spin isomers. These pairing gap energies at high-spin states are as large as those of the ground states, even though isomers have oblate shapes(β ∼ −0.19).

Chemical Bonds and Spin State Splittings in Spin Crossover Complexes. A DFT and QTAIM Analysis

Density functional theory (DFT) calculations have been performed for the high-spin (HS) and low-spin (LS) isomers of a series of iron(II) spin crossover complexes with nitrogen ligands. The calculated charge densities have been analyzed in the framework of the quantum theory of atoms in molecules (QTAIM). For a number of iron(II) complexes with substituted tris(pyrazolyl) ligands the energy difference between HS and LS isomers, the spin state splitting, has been decomposed into atomic contributions in order to rationalize changes of the spin state splitting due to substituent effects.

High-spin isomer in 93Mo

The high-spin states of 93Mo have been studied by a 82Se( 16O, 5n) 93Mo reaction at a beam energy of 100 MeV using techniques of in-beam γ-ray spectroscopy. Measurements of γ-t, γ-γ-t coincidences, γ-ray angular distributions and γ-ray linear polarizations were performed. The high-spin isomer was found as a (39/2-) state at about 9.7 MeV. The near-yrast states in 93Mo were interpreted using the weak-coupling picture of a d5/2 neutron to a neutron magic core nucleus 92Mo.

High-spin isomers and three-neutron valence configurations in 211Pb

High-spin isomers and three-neutron valence configurations in 211Pb

High-spin isomers and three-neutron valence configurations in 211Pb

Deep-inelastic reactions between a beam of 1360 MeV 208Pb ions and a thick 238U target have been used to populate the neutron-rich nucleus 211Pb. The observation of its γ decay has allowed identification of excited states up to the highest spin which can be formed from the three valence neutrons, including identification of three high-spin isomers. Level energies and transition strengths are compared to shell-model calculations with empirical interactions and predictions are made for the expected behaviour of more neutron-rich lead isotopes. The evidence for a possible increase in the neutron effective charge moving away from the N=126 shell gap is evaluated.

Application of the high-spin isomer beams to the secondary fusion reaction and the measurement of g-factor

A technique for providing high-spin isomers as probes of the fusion reaction and the measurement of g-factor has been worked out at RIKEN. In the study of the fusion reaction 12C(145mSm,xn)157−xEr, the γ rays emitted from the fusion-evaporation residue 154Er have been successfully observed. The nuclear g-factor of the T1/2 = 28 ns high-spin isomer in 149Dy has been measured with the γ-ray TDPAD method.

Studies of β-delayed proton decays of N≃Z nuclei around 100Sn at the GSI-ISOL facility

Beta decays of 94,96Ag and 103Sn nuclei into proton channels have been studied in the recent experiments at the GSI-ISOL facility. New efficient and chemically selective ion sources provided the highest yields of light silver and tin isotopes. Large arrays of germanium γ-ray and silicon charged-particle detectors, as well as a total absorption spectrometer (TAS) were used to measure β-proton, proton-γ, β-proton-γ and proton-γ-γ spectra. For the decay of 94Ag, we observed high-spin states in 93Rh populated by proton emission following β decay, whose largest spin value (≥39/2) yields an experimental proof for the existence of a second high-spin isomer in 94Ag with I≥17. Its β-decay energy is at least 16.8 MeV, corresponding to an excitation energy ≥5.5 MeV. For 103Sn, the γ rays measured in coincidence with β-delayed protons allowed us to establish the β-decay properties of this isotope. In particular, a QEC value of 7.5(6) MeV is derived from the intensity ratio of protons that are preceded either by EC or by β+ decays and populate the 2+ state in 102Cd.

β-delayed proton decay of a high-spin isomer inA94g

The decay of the (7{sup +}) and (21{sup +}) isomers of the N=Z isotope {sup 94}Ag was studied at the GSI on-line mass separator by measuring {beta}-delayed protons, {gamma} rays, proton-{gamma} and proton-{gamma}-{gamma} coincidences as well as the {beta}-strength distribution. We have observed high-spin (up to 39/2) states in {sup 93}Rh populated by proton emission following the {beta} decay of the {sup 94}Ag isomers. The major part of the population is related to the {beta} decay of the known (7{sup +}) isomer whose half-life is 0.61(2) s. The assignment of the high-spin (21{sup +}) isomer in {sup 94}Ag with a half-life of 0.39(4) s has been confirmed. The excitation energy and {beta}-decay energy of the (21{sup +}) isomer were measured to be at least 5.4 and 17.7 MeV, respectively. At this excitation energy, the (21{sup +}) isomer is expected to be unbound to direct one-proton, two-proton, or {alpha} decays. The remarkably long half-life of the (21{sup +}) isomer with the highest spin and excitation energy ever observed for {beta}-decaying nuclei makes a new textbook example of a nuclear high-spin trap. The branching ratios for {beta}-delayed proton emission are about 20% and 27% for the decays of the (7{sup +}) andmore » (21{sup +}) isomers, respectively. The properties of the experimentally identified {sup 93}Rh levels are discussed in comparison to shell-model predictions.« less

γ-ray spectroscopy ofBi191,193

Prompt and delayed γ rays from Bi191,193 have been identified using the recoil-decay tagging, isomer tagging, and recoil gating techniques, resulting in extensive level schemes for both nuclei. Excitation energies of the isomeric 13∕2+ states have been established and oblate strongly coupled bands built on them have been observed. The nearly spherical 9∕2− ground-state bands appear to be crossed by more oblate-deformed low-lying structures. The properties of the bands feeding the 1∕2+ intruder states indicate some structural change between Bi193 and Bi191. The deformation associated with each of these states has been extracted from total Routhian surface calculations which also reveal the development of prolate minima with decreasing neutron number. B(M1)∕B(E2) ratios have been measured for the observed strongly coupled bands in order to resolve the intrinsic excitations. The observed quasiparticle structures in Bi193 and high-spin isomers both in Bi193 and Bi191 are interpreted based on the coupling of the odd proton to the even-even Pb core.11 MoreReceived 2 December 2003DOI:https://doi.org/10.1103/PhysRevC.69.064326©2004 American Physical Society

Yield of radionuclides and isomers produced in the fragmentation of natW and 186W (97%) targets with protons at 630, 420 and 270 MeV

Yields and cross-sections of the radioactive nuclides produced after the irradiation of natural composition W and enriched 186W targets at the Dubna synchrocyclotron were measured using the γ-ray spectroscopy methods with high-resolution Ge detectors. Among the detected nuclides we identified the spallation and fission products. High-spin isomeric states in the Hf and Lu nuclides were populated and the isomer-to-ground state ratios could be estimated. The nuclide yields were calculated using the LAHET code at six different values of the proton energy in the range from 100 to 800 MeV both for the natW and enriched 186W targets. The measured isotope yields are in general good agreement with the calculations. A shortcoming of the code is the inability to predict isomer-to-ground state ratios. The experimental data show that the 177mLu, 178m2Hf and 179m2Hf high-spin isomers are produced with a 2.5 times higher yield in the 97% enriched 186W target as compared to the natW target under identical irradiation conditions. This makes significance for the creation of high-activity isomeric sources. The mass-distribution of the products and the fission-to-spallation ratio were also deduced and compared with theory prediction.

Isomer decay tagging in the heavy nuclei:Ra210andRa209

Excited states in $^{210}\mathrm{Ra}$ and $^{209}\mathrm{Ra}$ were populated using the $^{184}\mathrm{W}(^{30}\mathrm{Si},xn)$ reaction at $148\phantom{\rule{0.3em}{0ex}}\text{MeV}$ beam energy. Fusion evaporation recoils were selected using the gas-filled spectrometer, SASSYER. Prompt $\ensuremath{\gamma}$ rays were detected using Compton-suppressed Ge detectors from the YRAST Ball array surrounding the target. Delayed $\ensuremath{\gamma}$ rays, following isomeric decays, were detected at the focal plane of SASSYER with a smaller array of Ge detectors. The decay energy and lifetime for the ${8}^{+}{(\ensuremath{\pi}{h}_{9∕2})}^{n}$ isomer of $^{210}\mathrm{Ra}$ were determined; values for the yrast $B(E2;{8}^{+}\ensuremath{\rightarrow}{6}^{+})$ in $^{210}\mathrm{Ra}$ and neighboring nuclei are interpreted within the seniority scheme. This isomer was also used to select $\ensuremath{\gamma}$-rays deexciting levels above the isomeric state in $^{210}\mathrm{Ra}$. In addition, transitions in $^{209}\mathrm{Ra}$ were identified for the first time. Two high-spin isomers are suggested to exist in this isotope.

On the β-decaying (21 +) spin gap isomer in 94Ag

The β decay of 94Ag, a nucleus with three proton and three neutron holes with respect to 100Sn, was investigated at the GSI on-line mass separator by using an array of germanium and silicon detectors. On the basis of a βγγ coincidence measurement, the previously reported decay scheme has been considerably improved and evidence is presented for a spin–gap isomer with a spin-parity assignment of (21 +), i.e., the highest spin ever observed in β decay. The half-life of the low-spin isomer (7 +) was remeasured to be 0.59(2) s, whereas the half-life of the high-spin isomer was determined as 0.47(8) s. For the states in 94Ag and 94Pd, large-scale shell-model calculations that include up to 4p–4h excitations across the N= Z=50 shell gap and employ a realistic interaction were carried out. These core excitations play a crucial role in generating the E4 isomerism required for the interpretation of the long half-life of the (21 +) state in 94Ag.

Lifetime of a new high-spin isomer in 150 Dy

A new high-spin isomer in 150Dy has been observed at an excitation energy of 10.3 MeV by combining the inverse-kinematic reaction induced by a pulsed beam of 132Xe and the $\gamma$ -ray recoil-shadow technique. The half-life of this isomeric state has been determined to be $T_{1/2} = 1.6 \pm 0.6$ ns using the conventional centroid-shift method with the 141Pr(16O, p6n)150Dy reaction at 165 MeV. The mechanism producing high-spin isomers in N = 83,84 isotones is qualitatively discussed in terms of the difference of the neutron particle-hole configuration between the high-spin isomer and the lower-lying state.

G-Factor of the high-spin isomer in 149Dy and a multi-quasiparticle configuration caused by the N=82 core excitations

The nuclear g-factor of the T 1/2 = 28 ns high-spin isomer in 149Dy has been measured using the γ-ray time-differential perturbed angular distribution (TDPAD) technique with a pulsed beam of 132Xe. The experimental value g=+0.41(6) is in good agreement with a fully aligned multi-quasiparticle configuration π( h 2 11/2)⊗ ν( f 7/2 h 9/2 i 13/2( d −2 3/2) 0). This result indicates that only neutron particle–hole excitations across the N=82 shell-closure occur at this isomeric state.

High-spin states, lifetime measurements and isomers in 181Os

The level scheme of 181 76Os has been investigated with the 150Nd( 36S,5n) reaction. The low- K rotational bands built upon the 9/2 +[624], 7/2 −[514] and 1/2 −[521] neutron configurations have been extended and other new bands established. The configurations of these low- K bands are discussed within the framework of the cranked-shell model. The lifetimes for some of the states in the 9/2 +[624] and 1/2 −[521] collective rotational bands were also measured using the Doppler Shift Attenuation method. The large deformations deduced are found to be consistent with those predicted from theoretical Total Routhian Surface calculations. These results support the idea that for these low- K states the nuclear shape is axially symmetric and allows the K quantum number to be defined and the associated K-selection rule to be upheld. This behaviour apparently contrasts with that of the higher- K states in 181Os. In the higher-spin regime, two new high- K intrinsic states, with K π =37/2 + and K π =41/2 +, were established, along with the fragmented decay of a K π =33/2 − intrinsic state. The configurations and excitation energies of these experimentally determined intrinsic states are found to be in excellent agreement with theoretical calculations based on a fixed shape Nilsson model plus BCS pairing. The structures on top of these intrinsic states do, however, show very different behaviour. A relatively regular high- K rotational band was observed on top of the K π =41/2 + state but not for the other newly-established intrinsic states. Theoretical configuration-constrained potential energy surface calculations suggest that the irregular transition sequence above the K π =37/2 + intrinsic bandhead state, the limited excitations observed above the other intrinsic states and the observation of fragmented and non-hindered decays, are due to these configurations being subject to an appreciable γ softness. These calculations reveal that the K π =41/2 + configuration is less susceptible to distortions in the γ plane than any of the other high- K states.