Parity Assignments Research Articles

Detailed study of the decay of 21\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{21}$$\\end{document}Mg

Beta-delayed proton and gamma emission in the decay of 21\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{21}$$\\end{document}Mg has been measured at ISOLDE, CERN with the ISOLDE Decay Station (IDS) set-up. The existing decay scheme is updated, in particular what concerns proton transitions to excited states in 20\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{20}$$\\end{document}Ne. Signatures of interference in several parts of the spectrum are used to settle spin and parity assignments to highly excited states in 21\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{21}$$\\end{document}Na. The previously reported β\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta $$\\end{document}pα\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha $$\\end{document} branch is confirmed. A half-life of 120.5(4) ms is extracted for 21\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{21}$$\\end{document}Mg. The revised decay scheme is employed to test mirror symmetry in the decay and to extract the beta strength distribution of 21\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{21}$$\\end{document}Mg that is compared with theory.

β decay of the ground state and of a low-lying isomer in Bi216

A detailed β-decay study of the low- and high-spin states in Bi216 has been performed at the ISOLDE Decay Station at the CERN-ISOLDE facility. In total, 48 new levels and 83 new transitions in the β-decay daughter Po216 were identified. Shell-model calculations for excited states in Bi216 and Po216 were performed using the H208 and the modified Kuo-Herling particle effective interactions. Based on the experimental observations and the shell-model calculations, the most likely spin and parity assignments for the β-decaying states in Bi216 are (3−) and (8−), respectively. Published by the American Physical Society 2024

Ne21 energy levels approaching the α -particle threshold

Nuclei around Ne20 exhibit an interplay of different excitations caused by different aspects of nuclear structure, including single-particle and multiparticle configurations and collective rotations. One-nucleon transfer reactions selectively probe single-particle structures in these nuclei. These nuclei are also important to astrophysics, with a number of important reactions proceeding through this mass region. Energy levels approaching the α-particle threshold in Ne21 are of importance to nuclear structure. The Ne20(d,p)Ne21 reaction was measured and the corresponding spectroscopic nuclear information was extracted. States in Ne21 were populated using the Ne20(d,p)Ne21 reaction in forward kinematics. Protons were identified in the Triangle Universities Nuclear Laboratory (TUNL) Enge split-pole spectrograph and angular distributions were extracted. Spin-party assignments were made and neutron partial widths were determined based on distorted-wave Born approximation (DWBA) analysis. Several new energy levels were observed at energies of 7176, 7235, 7250, and 7337 keV, and spin-parities are reported which generally agree with previous results where literature was available. Spin and parity assignments are reported for several energy levels along with estimated neutron widths for those states above the neutron threshold (Sn=6761keV). Results from this study are placed in context with a review of the available literature on all known states in this energy region of Ne21.Published by the American Physical Society2024

Systematics of log [formula omitted] values for [formula omitted]−, and EC/[formula omitted]＋ transitions

This work is an update of the 1998 publication by Singh et al. [1] and reviews the logft values for all the known β-decay branches (β−, β＋/EC). Furthermore, an update of all Q-values (from AME2020 [2]), as well as a recalculation of all the logft values (through BetaShape code [3,4]) has been conducted using relevant data in the ENSDF database, as well as in newer literature. Only those cases have been considered in this review, where the beta transitions occur between levels of firm single spin assignments (86% of the transitions), and with probable single spin assignments (14% of the transitions), but with firm parity assignments for all the transitions. Weak β branches of <1% intensity in complex decay schemes have generally been omitted. Out of a total of 26318 β transitions extracted from the ENSDF database and current literature, data for only 4038 β transitions survived the filtering criteria in the present review. The logft values in β decay, spanning about 21 orders of magnitude, have been classified into allowed and forbidden categories according to the classification scheme of Konopinski [5]. All logft values have been deduced using the BetaShape code with new developments presented in this study. A very few number of logft values for very low-energy beta transitions (<5keV) survived the cut criteria and are briefly discussed in terms of atomic overlap corrections. Also tabulated and briefly discussed are seven superallowed cases with ΔT = 0, Tz(parent) = −2, while a known case for 28S to 28P has been omitted as reliable EC/β＋feeding to the analog state in 28P cannot be assigned due to lack of adequate experimental and detailed data for this decay. Centroid, width, minimum and maximum values for each category have been deduced. Uncertainties have been estimated and are also given. For literature coverage in the present review, see discussion in text.

Level scheme study of Mo91 : Weak-coupling approximation in the N=50 region

The level scheme of $^{91}\mathrm{Mo}$ has been studied using the GALILEO $\ensuremath{\gamma}$-ray spectrometer at Laboratori Nazionali di Legnaro, INFN. Five transitions together with four levels are identified for the first time by the $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence measurement, considerably enriching the negative band in $^{91}\mathrm{Mo}$. The discrepancy in the previous parity assignments for the states higher than 3807.5 keV has been clarified with the help of new experimental results. A shell-model calculation employing the JUN45 interaction is performed in order to get a further understanding of the level structure of $^{91}\mathrm{Mo}$. Being close to $N=50$ shell closure, the weak-coupling approximation between the valence ${g}_{9/2}$ neutron-hole with the even-even core $(^{92}\mathrm{Mo})$ is discussed in $^{91}\mathrm{Mo}$.

First spectroscopic study of odd-odd Cu78

Nuclei in the vicinity of Ni78 are important benchmarks for nuclear structure, which can reveal changes in the shell structure far from stability. Spectroscopy of the odd-odd isotope Cu78 was performed for the first time in an experiment with the EURICA setup at the Radioactive Isotope Beam Factory at RIKEN Nishina Center. Excited states in the neutron-rich isotope were populated following the β decay of Ni78 produced by in-flight fission and separated by the BigRIPS separator. A level scheme based on the analysis of γ−γ coincidences is presented. Tentative spin and parity assignments were made when possible based on the β-decay feeding intensities and γ-decay properties of the excited states. Time correlations between β and γ decay show clear indications of an isomeric state with a half-life of 3.8(4) ms. Large-scale Monte Carlo shell-model calculations were performed using the A3DA-m interaction and a valence space comprising the full fp shell and the 1g9/2 and 2d5/2 orbitals for both protons and neutrons. The comparison of the experimental results with the shell-model calculations allows interpreting the excited states in terms of spin multiplets arising from the proton-neutron interaction. The results provide further insight into the evolution of the proton single-particle orbitals as a function of neutron number, and quantitative information about the proton-neutron interaction outside the doubly magic Ni78 core.Received 6 October 2022Revised 3 January 2023Accepted 9 January 2023DOI:https://doi.org/10.1103/PhysRevC.107.044301©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBeta decayEnergy levels & level densitiesIsomer decaysNuclear spin & parityNuclear structure & decaysNucleon-nucleon interactionsShell modelProperties59 ≤ A ≤ 89Nuclear Physics

Nuclear magnetic moment of the neutron-rich nucleus O21

The ground-state magnetic dipole moment of the neutron-rich $^{21}\mathrm{O}$ isotope has been measured via $\ensuremath{\beta}$-ray-detected nuclear magnetic resonance ($\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{NMR}$) spectroscopy by using a spin-polarized secondary beam of $^{21}\mathrm{O}$ produced from the $^{22}\mathrm{Ne}$ primary beam. From the present measurement, the $g$ factor $|{g}_{\mathrm{exp}}(^{21}\mathrm{O}_{\mathrm{g}.\mathrm{s}.})|=0.6036(14)$ has been determined. Based on the comparison of this value with Schmidt values, we unambiguously confirm the $\ensuremath{\nu}{d}_{5/2}$ configuration with spin and parity assignments ${I}^{\ensuremath{\pi}}=5/{2}^{+}$ for the $^{21}\mathrm{O}$ ground state, suggested by previously reported studies. Consequently, the magnetic moment has been determined as ${\ensuremath{\mu}}_{\mathrm{exp}}(^{21}\mathrm{O}_{\mathrm{g}.\mathrm{s}.})=(\ensuremath{-})1.5090(35){\ensuremath{\mu}}_{N}$. The obtained experimental magnetic moment is in good agreement with the predictions of the shell-model calculations using the USD, YSOX, and SDPF-M interactions as well as random phase approximation (RPA) calculations. This observation indicates that the $^{21}\mathrm{O}$ nucleus in its ground state does not manifest any anomalous structure and is not influenced by the proximity of the drip line.

β decay of neutron-rich Cu76 and the structure of Zn76

The $\ensuremath{\beta}$ decay of $^{76}\mathrm{Cu}$ to the levels of $^{76}\mathrm{Zn}$ was studied at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Lab (ORNL). A purified $^{76}\mathrm{Cu}$ beam was developed and data were recorded for the decay of the $A=76$ decay chain using four high-purity germanium (HPGe) clover detectors at the Low-energy Radioactive Ion Beam Spectroscopy Station (LeRIBSS). In this measurement, data on \ensuremath{\gamma}-ray emission following $\ensuremath{\beta}$ decay, including $\ensuremath{\beta}\ensuremath{\gamma}$ and $\ensuremath{\gamma}\ensuremath{\gamma}$ coincidences, were collected and $\ensuremath{\gamma}\ensuremath{\gamma}$ spectra were analyzed to identify the statistically significant coincidences. From this analysis, we propose a level scheme for $^{76}\mathrm{Zn}$ which contains a total of 59 energy levels up to 6.0 MeV containing 105 $\ensuremath{\gamma}$ rays. We have identified an additional 53 $\ensuremath{\gamma}$ rays associated with this decay which could not be place in the decay scheme due to insufficient coincidence information or no energy match to identified levels. No $\ensuremath{\gamma}$ rays from states in $^{75}\mathrm{Zn}$ fed in the delayed-neutron branch were observed even though other $\ensuremath{\gamma}$ rays in the $A=75$ decay chain were observed. Spin and parity assignments are proposed for some levels based on comparison to systematics and shell model calculations.

Systematic trends of 0[formula omitted], 1[formula omitted], 3[formula omitted] and 2[formula omitted] excited states in even-even nuclei

The spin and parity (Jπ) assignments in even-even nuclei were reviewed across the nuclear chart using the Evaluated Nuclear Structure Data File (ENSDF). The prevalence of 21+ first or lowest excited states is confirmed. The properties of 02+, 11−, and 31− lowest excited states were reexamined using the ENSDF data evaluation procedures. The Jπ systematic trends and correlations between level quantum numbers and nuclear physics phenomena are discussed.

Experimental evidences of shape co-existence in 154Ho

The excited states of odd-odd 154Ho nucleus have been studied by the 141Pr(16O, 3n)154Ho reaction at Elab= 82 MeV utilizing the Indian National Gamma Array (INGA) setup at BARC-TIFR Pelletron facility, Tata Institute of Fundamental Research, Mumbai. Data from γ−γ coincidence, directional correlation (DCO), and polarization measurements have been analyzed to assign and confirm the spins and parities of the levels. The reported level scheme of 154Ho has been improved by including new levels and transitions. Mixing ratios for the mixed transitions extracted from DCO ratios and parity assignments from polarisation data are reported for the first time. The low-lying states in H154o, which are mostly collective, characterized by regularity in the excitation spectra, are proposed to be arising from neutron excitation. At higher excitation, there is a transition from collective to single-particle character, accompanied by the appearance of irregular and complex structure caused by proton excitation. The newly identified E1 gamma transitions connecting the low-lying positive and negative parity bands indicate octupole correlation in 154Ho. These new connections also support the phenomenological analysis to interpret the observed experimental features from a different perspective.

Improved Mo95 neutron resonance parameters and astrophysical reaction rates

Background: Improved $^{95}\mathrm{Mo}$ neutron resonance parameters and reaction rates are important for nuclear astrophysics, testing nuclear models, and nuclear criticality safety. However, despite many previous neutron-capture and total cross-section measurements on this nuclide, there still is much room for improvement as well as several discrepancies. For example, there are very few firm resonance spin and parity assignments; average resonance parameters are available only for each parity, the currently recommended astrophysical reaction rate results in disagreements between stellar models and meteoric isotopic anomalies, and there are substantial disagreements in the neutron-capture cross section at low energies important for nuclear criticality safety.Purpose: To obtain an improved set of neutron resonance parameters and astrophysical reaction rates for $^{95}\mathrm{Mo}$.Method: High-resolution neutron-capture and transmission data were measured at the Oak Ridge Electron Linear Accelerator (ORELA) using highly isotopically enriched $^{95}\mathrm{Mo}$ samples. The neutron-capture apparatus, data reduction, and analysis were improved so that information contained in the $\ensuremath{\gamma}$-ray cascade following neutron capture were used to assign resonance ${J}^{\ensuremath{\pi}}$ values. Following this, simultaneous analysis of the new neutron-capture and transmission data was used to obtain resonance energies, gamma widths, and neutron widths and their uncertainties to a maximum energy of 10 keV. Accurate neutron-capture cross sections also were obtained for the unresolved resonance region to a maximum energy of 500 keV and, together with the new resonance parameters, used to calculate the astrophysical reaction rates in the temperature range from 5 to 30 keV.Results: A vastly improved set of $^{95}\mathrm{Mo}$ neutron resonance parameters and an astrophysical reaction rate accurate to about 3% were obtained. Firm ${J}^{\ensuremath{\pi}}$ assignments were determined for 261 of the 314 observed resonances. This is a very large improvement over the previously published 32 firm ${J}^{\ensuremath{\pi}}$ assignments for 108 resonances. Also, the number of resonances having both firm ${J}^{\ensuremath{\pi}}$ assignments and ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}}$ values was increased by almost a factor of 24---from 11 to 261. Neutron- and total-radiation-width distributions and average resonance spacings, average total radiation widths, and neutron strength functions were obtained for the six different $s$- and $p$-wave possibilities. Parameters for the lowest $s$-wave resonance, which is most important for criticality benchmarks, were obtained with high accuracy.Conclusions: Simple modification of the neutron-capture apparatus and expansion and improvement of data analysis techniques led to a large increase in firm ${J}^{\ensuremath{\pi}}$ assignments for $^{95}\mathrm{Mo}$ neutron resonances. The resulting astrophysical reaction rate is 20%--30% larger than the currently recommended rate at $s$-process temperatures, which should lead to better agreement between stellar models and meteoric isotopic anomalies. The neutron-capture cross section at low energies is substantially larger than recommended in the latest evaluation, which is problematical for criticality benchmarks. The average resonance spacing as a function of spin and parity is significantly different from current models. The total-radiation-width distributions are significantly broader than predicted by theory and show significant departures from the expected Gaussian shapes.

The effect of hidden-charm strange pentaquarks Pcs on the K− p → J/ψ Λ reaction

We present a recent investigation on the production of Pcs (4459) in the K− p → J/ψΛ reaction, using both the effective Lagrangian and Regge approaches. We assume six different spin and parity assignments, i.e., 1/2± , 3/2± and 5/2± to the newly found Pcs. The total and differential cross sections for the K− p → J/ψΛ reaction are calculated. We examine the dependence of the results on the different assignments of JP for Pcs.

First observation of the π0h11/2⊗ν0h9/2 partner orbital configuration in the odd-odd I138 nucleus

The β-decay scheme of Te138 and the level structure of I138 is reported for the first time. The experiment was performed at the Radioactive Isotope Beam Factory of RIKEN, as one of the EUROBALL-RIKEN Cluster Array campaigns. Secondary radioactive ions, including Te138 and Sb138, were produced by the in-flight fission of a U238 beam with the energy of 345 MeV per nucleon. From the β decay of Te138, the level scheme of I138 was supplemented with new spin and parity assignments, such as the low-lying negative-parity states and a positive-parity 1+ state. This 1+ state can be interpreted as being associated with the π0h11/2⊗ν0h9/2 partner orbital configuration populated by the Gamow-Teller transition between a neutron in the 0h9/2 orbital and a proton in the 0h11/2 orbital. Details of the structure of I138 are discussed in terms of the proton-neutron interactions and Gamow-Teller transition strength within the theoretical context of shell-model calculations.Received 5 December 2021Accepted 16 March 2022DOI:https://doi.org/10.1103/PhysRevC.105.034334©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBeta decayNuclear structure & decaysProperties90 ≤ A ≤ 149TechniquesRadiation detectorsRadioactive beamsShell modelSpectrometers & spectroscopic techniquesNuclear Physics

Determination of the Spin Axis in Quantum Spin Hall Insulator Candidate Monolayer WTe2

Evidence for the quantum spin Hall (QSH) effect has been reported in several experimental systems in the form of approximately quantized edge conductance. However, the most fundamental feature of the QSH effect, spin-momentum locking in the edge channels, has never been demonstrated experimentally. Here, we report clear evidence for spin-momentum locking in the edge channels of monolayer WTe2, thought to be a two-dimensional topological insulator (2D TI). We observe that the edge conductance is controlled by the component of an applied magnetic field perpendicular to a particular axis, which we identify as the spin axis. The axis is the same for all edges, situated in the mirror plane perpendicular to the tungsten chains at 40$\pm$2{\deg} to the layer normal, implying that the spin-orbit coupling is inherited from the bulk band structure. We show that this finding is consistent with theory if the band-edge orbitals are taken to have like parity. We conclude that this parity assignment is correct and that both edge states and bulk bands in monolayer WTe2 share the same simple spin structure. Combined with other known features of the edge states this establishes spin-momentum locking, and therefore that monolayer WTe2 is truly a natural 2D TI.

Ba145 and La145,146 structure from lifetime measurements

The occurrence of octupole shapes in even-mass neutron-rich Ba isotopes has been well established. However, the situation with the odd-mass Ba and odd or odd-odd La nuclei around them is not so clear. In order to shed light on these less-studied isotopes, a fast-timing experiment was performed using the GRIFFIN spectrometer at TRIUMF-ISAC. A wealth of excited-state lifetimes in the 100 ps to few ns range have been measured in $^{144,145,146}\mathrm{Ba}$ and $^{145,146}\mathrm{La}$ populated in the ${\ensuremath{\beta}}^{\ensuremath{-}}$ and ${\ensuremath{\beta}}^{\ensuremath{-}}\text{\ensuremath{-}}n$ decay of $^{145,146}\mathrm{Cs}$. The results do not allow one to draw firm conclusions about the possible octupole deformation of these nuclei but suggest different spin and parity assignments than previous works. This work highlights the need for more detailed study of the odd and odd-odd isotopes in this region to properly understand their structure.

Undetectable steganographic method for palette-based images

Steganography is a technique applied to ensure secure communication. It is challenged by visual observation or statistical analysis to ascertain whether a message is hidden within a cover medium. Several steganographic methods have been proposed for palette-based images. These methods maintain image quality but cannot resist some statistical and visual attacks. To overcome this problem, two parity assignments with performances similar to those of existing parity assignments are proposed. An innovative embedding process that randomly selects one parity assignment while embedding secret bits in each pixel is provided. Finally, a steganographic method using the proposed embedding process and a specified adaptive scheme is presented. Experimental results revealed that the proposed method is undetectable under some statistical and visual attacks even as it maintains image quality.

γ spectroscopy of the Y96 isotope: Searching for the onset of shape coexistence before N=60

Medium and high spin states of the Y96 nucleus, located in the shape-coexistence region near Z=40 and N=60, were populated in thermal-neutron-induced fission of U233 and U235 targets, diluted in a scintillator. γ rays were measured with the FIssion Product Prompt γ-ray Spectrometer (FIPPS) high-purity germanium (HPGe) detector array, using double and triple γ-ray coincidence techniques and taking advantage of the efficient fission tag provided by the scintillating target material. A complex level scheme, extending up to 5.2 MeV and including excitations above the 8+β-decaying isomer, was investigated, and firm spin and parity assignments were given to a number of states, on the basis of angular correlation analysis and considerations on the γ-decay patterns. While the structures built on the 0− ground state and the 8+ isomer show irregular patterns typical for spherical shapes, the (6+) isomeric state at 1655 keV [with half-life of 181(9) ns], and the rotational band built on it [with spin-parity values between (6+) and (9+)], can be explained by Hartree-Fock-Bogoliubov calculations, if an oblate deformation is assumed. This is the first observation of a deformed structure in an N=57 isotone, lying three neutrons away from the N=60 line. An important finding is also the 115-keV transition which connects the (6+) 181(9)-ns isomer to the β-decaying 8+ spherical isomer, allowing us to firmly place the latter at 1541 keV excitation energy. This may be relevant for calculations of electron and antineutrino spectra from fission of actinides, for which Y96 is a prominent product.8 MoreReceived 30 May 2020Revised 16 June 2020Accepted 25 August 2020DOI:https://doi.org/10.1103/PhysRevC.102.054324©2020 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCollective levelsElectromagnetic transitionsIsomer decaysLifetimes & widthsNuclear spin & parityNuclear structure & decaysProperties90 ≤ A ≤ 149Nuclear Physics

Spectroscopic study of Ca47 from the β− decay of K47

The $\beta^-$ decay of $^{47}$K to $^{47}$Ca is an appropriate mechanism for benchmarking interactions spanning the $sd$ and $pf$ shells, but current knowledge of the $\beta^-$-decay scheme is limited. We have performed a high-resolution, high-efficiency study of the $\beta^-$-decay of $^{47}$K with the GRIFFIN spectrometer at TRIUMF-ISAC. The study revealed 48 new transitions, a more precise value for the $^{47}$K half-life (17.38(3)~s), and new spin and parity assignments for eight excited states. Levels placed for the first time here raise the highest state observed in $\beta^-$ decay to within 568(3) keV of the $Q$-value and confirm the previously measured large $\beta^-$-decay branching ratios to the low-lying states. Previously unobserved $\beta^-$-feeding to 3/2$^+$ states between 4.5 and 6.1~MeV excitation energy was identified with a total $\beta^-$-feeding intensity of 1.29(2)\%. The sum of the $B(GT)$ values for these states indicates that the $1s_{1/2}$ proton hole strength near this excitation energy is comparable to the previously known $1s_{1/2}$ proton and neutron hole strengths near 2.6 MeV.

γ -ray and conversion-electron spectroscopy of the high-spin isomer in Sm145

Background: High-spin isomers at {\approx}9-MeV excitation energies have been reported in several N = 83 isotones near Z = 64. Spin and parity assignments of J{^\pi} = 49/2+ remain tentative for a number of these states in the odd-A nuclei. Purpose: To study the decay of the (49/2 +) high-spin isomer in 145 Sm, make firm spin and parity assignments to the isomer and states populated in its decay, and investigate the structure of the nucleus. Methods: The 145Sm isomer was populated in the 124Sn(26Mg,5n) reaction. Gamma-ray and conversion-electron data were collected using the Solenogam array. Results: A revised lifetime of t1/2 = 3.52(16) mus was measured for the high-spin isomer. Several new states have been added to the level scheme, and a new state at 8815 keV is proposed as the isomer, based on decay-property systematics, transition strengths, and spin and parity assignments. Firm spin and parity assignments have been made to states up to and including the isomer and the new level scheme is interpreted using shell-model calculations performed with the KShell program. Conclusions: The interpretation of the 49/2+ isomer as a deformed excitation of the core neutrons remains unchanged, although there has been a significant revision of the level scheme below the isomer, and hence significant reinterpretations of the lower-lying states.

Shell structure of S43 and collapse of the N=28 shell closure

The single-particle structure of the $N=27$ isotones provides insights into the shell evolution of neutron-rich nuclei from the doubly-magic $^{48}$Ca toward the drip line. $^{43}$S was studied employing the one-neutron knockout reaction from a radioactive $^{44}$S beam. Using a combination of prompt and delayed $\gamma$-ray spectroscopy the level structure of $^{43}$S was clarified. Momentum distributions were analyzed and allowed for spin and parity assignments. The deduced spectroscopic factors show that the $^{44}$S ground-state configuration has a strong intruder component. The results were confronted with shell model calculations using two effective interactions. General agreement was found between the calculations, but strong population of states originating from the removal of neutrons from the $2p_{3/2}$ orbital in the experiment indicates that the breakdown of the $N=28$ magic number is more rapid than the theoretical calculations suggest.