Neutron Core Excitations Research Articles

Shell model study of 92Mo and systematic features of the N = 50 isotones

The level structures of 92Mo have been investigated using the shell model code nushellx@msu within two large model spaces containing neutron core excitations across the N = 50 closed shell. The calculated results are compared with the available experimental data, and reasonable agreements are obtained. The level structures of 92Mo, especially the levels come from neutron core excitations, are interpreted by the present calculations. The systematic features of neutron core excitations in the even–even N = 50 isotones have also been investigated.

Core breaking and possible magnetic rotation in the semimagic nucleus 90Zr * *Supported by the National Natural Science Foundation of China (11775098, U1867210, 11405072), Jilin Scientific and Technological Development Programs (20190201137JC, 20180520195JH), the 13th Five-Year Plan of Scientific Research of Jilin Province (JJKH20180117KJ), China Postdoctoral Science Foundation (2015M571354, 2013M541285), the Fundamental Research Funds for the Central Universities, and the Graduate

The semimagic nucleus 90Zr, with Z = 40 and N = 50, is investigated in terms of large scale shell model calculations. A logical agreement is obtained between the available experimental data and predicted values. The calculated results indicate that the low-lying states are primarily dominated by the proton excitations from the fp orbitals across the Z = 38 or 40 subshell into the high-j orbital. For the higher-spin states of 90Zr, the breaking of the N = 50 core plays a crucial role, and the contribution of different orbitals to each state are discussed in this article. The evolution from neutron core excitations to proton excitations is systematically studied along the neighboring N = 50 isotones. Furthermore, the strong = 1 sequence demonstrates an abrupt backbend attributed to the alignment of the valence nucleons in fp proton orbitals and is proposed to have a configuration before the backbend, based on the shell model calculations. The properties of this sequence before the backbend indicate a general agreement with the fingerprints of magnetic rotation; hence, the sequence with the configuration is suggested as a magnetic rotational band arising from shears mechanism.

Analysis of low-lying states, neutron-core excitations, and electromagnetic transitions in tellurium isotopes Te130–134

The neutron-rich $^{130--134}\mathrm{Te}$ isotopes are investigated by large-scale shell-model calculations with the extended pairing plus multipole-multipole force (EPQQM model). The orbits of $(0{g}_{7/2},1{d}_{5/2},1{d}_{3/2},2{s}_{1/2},0{h}_{11/2})$ are included for both proton and neutron model space, while two more neutron orbits $(1{f}_{7/2},2{p}_{3/2})$ above the $N=82$ shell gap are included to study neutron-core excitations. The higher core-excited states in $^{132,133}\mathrm{Te}$ are calculated for the first time in this region. The present work well describes both the low-lying and the high-energy states for $^{134}\mathrm{Te}$, $^{133}\mathrm{Te}$, and $^{132}\mathrm{Te}$, as well as the low-lying levels of $^{131}\mathrm{Te}$ and $^{130}\mathrm{Te}$. The several multiplets with clear boundary exist in $^{134,133}\mathrm{Te}$, while a new configuration lying between 4.8 and 6.0 MeV is found as a theoretical prediction in $^{134}\mathrm{Te}$. Finally, the transition probabilities in these nuclei are calculated and compared with available data. The predicted energy levels and electromagnetic transition will be useful for planning future experiments.

Erratum: High-spin states in the semimagic nucleus Y89 and neutron-core excitations in the N=50 isotones [Phys. Rev. C 94 , 014315 (2016)

Erratum: High-spin states in the semimagic nucleus <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi mathvariant="normal">Y</mml:mi><mml:mprescripts /><mml:none /><mml:mn>89</mml:mn></mml:mmultiscripts></mml:math> and neutron-core excitations in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>N</mml:mi><mml:mo>=</mml:mo><mml:mn>50</mml:mn></mml:mrow></mml:math> isotones [Phys. Rev. C <b>94</b> , 014315 (2016)

Monopole effects, core excitations, and decay in the A= 130 hole nuclei near 132Sn * * Research at Zhoukou Normal University is supported by the National Natural Science Foundation of China (11505302). Research at China Institute of Atomic Energy is supported by the National Natural Science Foundation of China (11490563) and by the National Key Research and Development Program of

The proton and neutron cross-shell excitations across the Z= 50 shell are investigated in the southwest quadrant of 132Sn by large-scale shell-model calculations with extended pairing and multipole-multipole force. The model space allows proton (neutron) core excitations, and both the low- and high-energy states for 130In are well described, as found by comparison with the experimental data. The monopole effects between the proton orbit and neutron orbit are studied as the new monopole correction that perfectly reproduces the first 1+ level in 130In. The energy interval of proton (neutron) core excitations in 130In lies in the range of 4.5−6.5 (2.0−4.1) MeV, and the high energy yrast states are predicted as neutron core excitations. The decays are calculated among the A=130 nuclei of 130In, 130Sn and 130Cd.

Shell-model calculations for the semi-magic nucleus 85Br and systematic features of the N = 50 odd-A isotones**Supported by Natural Science Foundation of China (11622540, 11461141001, U1432119) and Computations were Carried Out on an HP Proliant DL785G6 Server Hosted by the Institute of Space Science of Shandong University

Level structures of 85Br have been investigated using the shell-model code nushellx within a large model space containing the neutron-core excitations across the N = 50 closed shell. The calculated results have been compared with the available experimental data. Reasonable agreement between the experimental and calculated values is obtained, which indicates that the neutron-core excitations are essential to reproduce the level structures of 85Br. The systematic features of neutron-core excitations in the N = 50 isotones are investigated.

High-spin states in the semimagic nucleusY89and neutron-core excitations in theN=50isotones

The semimagic nucleus $^{89}\mathrm{Y}$ has been investigated using the $^{82}\mathrm{Se}(^{11}\mathrm{B},4n)$ reaction at beam energies of 48 and 52 MeV. More than 24 new transitions have been identified, leading to a considerable extension of the level structures of $^{89}\mathrm{Y}$. The experimental results are compared with the large-basis shell model calculations. They show that cross-shell neutron excitations play a pivotal role in high-spin level structures of $^{89}\mathrm{Y}$. The systematic features of neutron-core excitations in the $N=50$ isotones are also discussed.

Spectroscopy ofP35using the one-proton knockout reaction

The structure of $^{35}$P was studied with a one-proton knockout reaction at88~MeV/u from a $^{36}$S projectile beam at NSCL. The $\gamma$ rays from thedepopulation of excited states in $^{35}$P were detected with GRETINA, whilethe $^{35}$P nuclei were identified event-by-event in the focal plane of theS800 spectrograph. The level scheme of $^{35}$P was deduced up to 7.5 MeV using$\gamma-\gamma$ coincidences. The observed levels were attributed to protonremovals from the $sd$-shell and also from the deeply-bound $p\_{1/2}$ orbital.The orbital angular momentum of each state was derived from the comparisonbetween experimental and calculated shapes of individual ($\gamma$-gated)parallel momentum distributions. Despite the use of different reactions andtheir associate models, spectroscopic factors, $C^2S$, derived from the$^{36}$S $(-1p)$ knockout reaction agree with those obtained earlier from$^{36}$S($d$,\nuc{3}{He}) transfer, if a reduction factor $R\_s$, as deducedfrom inclusive one-nucleon removal cross sections, is applied to the knockout transitions.In addition to the expected proton-hole configurations, other states were observedwith individual cross sections of the order of 0.5~mb. Based on their shiftedparallel momentum distributions, their decay modes to negative parity states,their high excitation energy (around 4.7~MeV) and the fact that they were notobserved in the ($d$,\nuc{3}{He}) reaction, we propose that they may resultfrom a two-step mechanism or a nucleon-exchange reaction with subsequent neutronevaporation. Regardless of the mechanism, that could not yet be clarified, thesestates likely correspond to neutron core excitations in \nuc{35}{P}. Thisnewly-identified pathway, although weak, offers the possibility to selectivelypopulate certain intruder configurations that are otherwise hard to produceand identify.

Nuclear Data Sheets for A = 87

The evaluated experimental data are presented for 14 known nuclides of mass 87 (Ga, Ge, As, Se, Br, Kr, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru). New datasets have been added for 87Ga, 87Se, 87Kr, 87Rb, 87Sr, 87Nb, and 87Tc. The observation of and new lifetime measurements for 87As at the NSCL Coupled Cyclotron Facility and the Oak Ridge Isochronous Cyclotron at the HRIBF–ORNL Facility are included in the adopted levels for this isotope. The new evaluation also includes an isomeric level at unknown energy for 87Tc, changes to the adopted levels for 87Nb based on newly published data including an extension of the high spin levels and new lifetime measurements, and new heavy ion data for 87Kr. New high spin levels for 87Rb were observed, indicating possible neutron core excitations. In addition, the ground state lifetime of 87Rb has been revised and a new lifetime measurement for an excited level in 87Rb indicates a possible proton spin flip. New excitation levels have been observed for the first time in 87Se. New direct and precise measurement of atomic masses of 87Tc, 87Mo, 87Nb, 87Zr, 87Mo and 87Tc have greatly improved the Q value landscape in this mass region. This work supersedes the previous A=87 evaluation published in 2002He09, and Q values for all isotopes were updated to incorporate the mass evaluation in 2012Wa38.

Large-scale shell-model calculation with core excitations for neutron-rich nuclei beyond132Sn

The structure of neutron-rich nuclei with a few nucleons beyond ${}^{132}$Sn is investigated by means of large-scale shell-model calculations. For a considerably large model space, including neutron core excitations, a new effective interaction is determined by employing the extended pairing-plus-quadrupole model with monopole corrections. The model provides a systematical description for energy levels of $A=133$--135 nuclei up to high spins and reproduces available data of electromagnetic transitions. The structure of these nuclei is analyzed in detail, with emphasis of effects associated with core excitations. The results show evidence of hexadecupole correlation in addition to octupole correlation in this mass region. The suggested feature of magnetic rotation in ${}^{135}$Te occurs in the present shell-model calculation.

Fission fragment isomers populated viaLi6+Th232

Short-lived isomers in fission fragments following bombardment of 45-MeV $^{6}\mathrm{Li}$ on $^{232}\mathrm{Th}$ were examined. Isomers in the $A~95,122,$ and 132 mass regions were observed. New isomeric decays were observed in $^{121}\mathrm{In}$ [${T}_{1/2}=17(2) \ensuremath{\mu}$s], $^{123}\mathrm{In}$ (${T}_{1/2}\ensuremath{\gtrsim}100 \ensuremath{\mu}$s), and $^{125}\mathrm{Sb}$ [${T}_{1/2}=25(4) \ensuremath{\mu}$s]. These isomers are suggested to arise from $\ensuremath{\nu}({h}_{11/2}\ensuremath{\bigotimes}{d}_{3/2}){7}^{\ensuremath{-}}$ and $\ensuremath{\nu}({h}_{11/2}\ensuremath{\bigotimes}{s}_{1/2}){5}^{\ensuremath{-}}$ neutron core excitations coupling with the valence proton.

Structure of theN=126nuclideRn212: Valence and core excited configurations

The level scheme of $^{212}\mathrm{Rn}$ has recently been expanded and extended to spins of $~39\ensuremath{\hbar}$ and excitation energies of about 13 MeV using the $^{204}\mathrm{Hg}$($^{13}\mathrm{C}$,$5n$)$^{212}\mathrm{Rn}$ reaction and $\ensuremath{\gamma}$-ray spectroscopy. Time-correlated techniques were used to obtain channel selectivity and improved sensitivity. New $\ensuremath{\gamma}$-ray branches from states associated with valence proton configurations as well as a number of new states below the ${22}^{+}$ isomer have been identified. The excitation energy of the ${22}^{+}$ core excited isomer itself has been established through the observation of several branches parallel to the main decay, implying a transition energy of $7.6$ keV for the previously unobserved decay to the ${20}_{2}^{+}$ state. The level scheme above the ${22}^{+}$ isomer includes two new isomers with $\ensuremath{\tau}=25(2)$ ns and $\ensuremath{\tau}=12(2)$ ns placed at $12,211$ and $12,548$ keV, respectively. These are attributed to configurations involving triple neutron core excitations coupled to the aligned valence protons. The results are compared to semiempirical shell-model calculations, which can account for many of the states observed, with considerable precision for the valence proton configurations but with significant energy discrepancies for some core excited configurations. Calculations within the deformed independent particle model (DIPM) have also been carried out for the main core excited configurations at high spin and compared with both experiment and the empirical shell-model approach. The possible sources of discrepancies in both approaches are discussed, and it is suggested that anomalously low excitation energies are predicted for specific configurations in the DIPM.

High-spin isomers in 212Rn in the region of triple neutron core-excitations

The level scheme of 212Rn has been extended to spins of ∼38ℏ and excitation energies of about 13 MeV using the 204Hg(13C, 5n)212Rn reaction and γ-ray spectroscopy. Time correlated techniques have been used to obtain sensitivity to weak transitions and channel selectivity. The excitation energy of the 22+ core-excited isomer has been established at 6174 keV. Two isomers with τ=25(2) ns and τ=12(2) ns are identified at 12211 and 12548 keV, respectively. These are the highest-spin nuclear isomers now known, and are attributed to configurations involving triple neutron core-excitations coupled to the aligned valence protons. Semi-empirical shell-model calculations can account for most states observed, but with significant energy discrepancies for some configurations.

High-spin states inN=50Br85andRb87nuclei

The level structures of the $N=50$ $^{85}\mathrm{Br}$ and $^{87}\mathrm{Rb}$ isotopes have been studied in the fission of the compound system formed in three different heavy-ion-induced reactions. In $^{87}\mathrm{Rb}$ many states above the previously known 9/2${}^{+}$ isomer have been established. The coupling of the odd proton occupying the ${g}_{9/2}$ orbital to the yrast states in the $^{86}\mathrm{Kr}$ core can account for the first excited states above the isomer in $^{87}\mathrm{Rb}$. A comparison with the first excited states above the 9/2${}^{+}$ state in $^{85}\mathrm{Kr}$ and $^{89}\mathrm{Y}$ reveals similarities in the coupling. At higher excitations similar behavior to $^{89}\mathrm{Y}$ is observed, indicating a possible presence of neutron-core excitations. In $^{85}\mathrm{Br}$ several states up to ~5 MeV excitation energy have been established. Two states at ~2 MeV excitation energy are candidates for the 9/2${}^{+}$ state originating from the odd proton occupying the ${g}_{9/2}$ orbital. The experimental results for both isotopes are compared with predictions of the shell model.

High spin states in 210Rn approaching the region of 3-particle–hole neutron excitations

The properties of high spin states in 210Rn have been investigated using the 198Pt( 17O, 5 n) reaction at a bombarding energy of 96 MeV. Decay properties for states up to an excitation energy of 12026 + Δ keV and spin of (37 −) have been deduced. The level scheme is compared with predictions of empirical shell model calculations. High lying states are interpreted in terms of multiparticle configurations which include single and double neutron core excitations. Configurations have been assigned for almost all of the observed levels. Agreement between experimental and calculated level energies is generally within 200 keV.

Influence of neutron-core excitations on high-spin states in88Sr

High-spin states of the nucleus ${}^{88}\mathrm{Sr}$ have been studied via the reaction ${}^{80}\mathrm{Se}{(}^{11}\mathrm{B},p2n)$ at a beam energy of 45 MeV. Gamma rays were detected with the six-detector array OSIRIS CUBE. The level scheme of ${}^{88}\mathrm{Sr}$ has been extended up to $E\ensuremath{\approx}11 \mathrm{MeV}$ and $J=17.$ Mean lifetimes of three levels have been determined using the Doppler-shift-attenuation method. The level structures in ${}^{88}\mathrm{Sr}$ have been interpreted in terms of the shell model. The calculations were performed in the configuration space ${(0f}_{5/2}{,1p}_{3/2}{,1p}_{1/2}{,0g}_{9/2})$ for the protons and ${(1p}_{1/2}{,0g}_{9/2}{,1d}_{5/2})$ for the neutrons. These calculations describe the high-spin level sequences linked by $M1$ transitions with strengths of $B(M1)\ensuremath{\approx}0.3$ to 1.4 W.u. as multiplets of seniority $\ensuremath{\upsilon}=4$ and 6 states including proton configurations and neutron-core excitations.

Neutron-core excitations in 8636Kr50

Shell-model calculations for the N = 50 nucleus 86Kr are presented and compared to results of recent in-beam experiments. Two model spaces are considered: a pure proton configuration space containing the 0f5/2, 1p=3/2, 1p½, 0g=9/2 orbitals and a model space including additionally the particle-hole excitation generated by one neutron lifted from the 0g9/2 orbital across the shell gap to the 1d=5/2 orbital. The predictions of the shell-model using various sets of residual interactions and based on pure proton excitations are comparable with the experimental findings for the states of positive parity below 4 MeV and for the negative-parity states with spins up to 7−. The inclusion of neutron-core excitations causes an improved agreement between experimental und calculated level energies for the positive-parity yrast states with spins 7h, 9h and 10h. The interpretation of neutron-core excited high-spin states is supported by the comparison of the level structure of 8636Kr50 to the experimental levels of the valence-mirror nucleus 6428Ni36.

Study of excited states in 85Kr and 86Kr: Evidence for neutron-core excitations in the N=50 nucleus 86Kr.

Study of excited states in 85Kr and 86Kr: Evidence for neutron-core excitations in the N=50 nucleus 86Kr.

Neutron-core excitations in the N=50 nucleus 89Y

High-spin states of the N=50 nucleus 89Y up to 312h̷ at 8.7 MeV have been investigated in the (α,2n) reaction by using in-beam γ-ray spectroscopy. Besides singles γ-ray spectra, excitation functions and γγ-coincidences, the angular distribution and linear polarization of the γ-rays have been measured. For 23 of the observed 28 levels, mean lifetimes or limits have been determined by means of the Doppler-shift attenuation of γ-r.f. methods. In order to calculate the stopping of recoils in the two-component RbCl target a new procedure had to be developed. On the basis of all these experiments several new levels as well as many spin/parity values could be uniquely assigned. The most surprising results are the observed high level density at spin 232and252 and the identification of several fast M1-transitions at high spin. Both results may be explained by the inclusion of neutron particle-hole excitations across the closed N=50 shell. No collective E2 transitions have been found. The experimental results are compared with shell model calculations.

Very-high-spin and core-coupled states in 213Rn. a test of the applicability of the deformed independent particle model

Excited states in 212,213Rn were populated in the bombardment of 204Hg by 14C ions of energies 80-94 MeV. The depopulation of the excited states was studied using in-beam spectroscopic methods including γ-ray excitation, γ-ray angular distribution, γ-γ-t coincidence, pulsed-beam-γ timing and conversion electron measurements. Spins up to Jπ = 30ℏ and a tentative J = (73/2)ℏ were observed, respectively. In 212Rn the previous level scheme was confirmed, with the addition of five new transitions of which one feeds the 30+ state. In 213Rn the previously reported level scheme was mainly confirmed and it was extended to (71/2) or (73/2)ℏ, which is the highest spin observed to-date in a lead-region nucleus. Several transition rates B(λ) were deduced from isomeric half-lives or branching ratios in both isotopes. Deformed Independent Particle Model (DIPM) calculations were performed to assign configurations, which in 213Rn usually consist of the odd neutrons vg9/2 and vj15/2 coupled to the four-proton states in 212Rn. The highest levels include neutron core-excitations, since the maximum valence-nucleon angular momentum in 213Rn is 55/2ℏ. The very topmost levels even need 2- particle-two-hole excitations. Shape changes in these two Rn isotopes are discussed, as are the transition rates.