Proposed Level Scheme Research Articles

Investigation of level structure in the semimagic nucleus Nb91 and systematics of nuclear structure characteristics near A=90

We report the new level scheme of the $^{91}\mathrm{Nb}$ nucleus established by the reactions $^{82}\mathrm{Se}(^{14}\mathrm{N},\phantom{\rule{4pt}{0ex}}5n)^{91}\mathrm{Nb}$ and $^{76}\mathrm{Ge}(^{19}\mathrm{F},\phantom{\rule{4pt}{0ex}}4n)^{91}\mathrm{Nb}$. Thirty new transitions with energies up to about 12 MeV are assigned to the $^{91}\mathrm{Nb}$ nucleus and placed in the proposed level scheme. The excited levels are well reproduced by shell-model calculations with the GWBXG effective interaction. The obtained results, which conform to the most experimental data well, manifest that the high spins are construed as the proton excitations from $1{p}_{3/2}$, $0{f}_{5/2}$, and $1{p}_{1/2}$ orbitals, to the $0{g}_{9/2}$ orbital with the breakup of the $Z=38$ (40) core, as well as neutron excitations from the $0{g}_{9/2}$ orbital to the $1{d}_{5/2}$ or $0{g}_{7/2}$ orbital with the breakup of the $N=50$ core.

Nuclear Data Sheets for A=98

Experimental spectroscopic data on nuclear structure and decay are evaluated for known nuclides of mass 98 (Br, Kr, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In). Detailed evaluation results of individual reactions and decays are presented together with the Adopted values that are recommended for level properties, γ and β radiations, and other spectroscopic information. 98Mo remains as the most extensively studied nuclide via various reactions and decays. Level schemes of Sr, Y, Zr, Tc, and Pd nuclides in this mass chain are also well established to date; while Kr, Rb, Nb, Ag and Cd are amongst the least-studied ones for excited states, with only limited data available for each. On the neutron-rich side, 98Br has been identified in the 9Be(238U,F) reaction, but no spectroscopic data are yet available, while for 98In on the proton-rich side, only the ground state and an isomer are known with half-lives measured but their spin-parities and the absolute level energy of the isomer yet to be determined. While 98Ru and 98Rh have also been extensively studied, large discrepancies exist between the high-spin sections of the proposed level schemes in different measurements, and these need to be clarified and resolved with further experimental investigations to improve the currently-adopted ones, which have been selected from the measurements with higher statistics, considering no other criteria of preference. This work supersedes all the earlier evaluations of A=98 (2003Si07, 1998Si18, 1992Si21, 1983Mu21, 1974Me34).

Observation of multiple doubly degenerate bands in 195Tl

The High-spin states in 195Tl, populated through the 185,187Re(13C, xn) fusion evaporation reaction at the beam energy of 75 MeV, were studied using the Indian National Gamma Array (INGA). More than 50 new γ transitions have been placed in the proposed level scheme which is extended up to the excitation energy of ≈ 5.6 MeV and spin=22.5ħ. Two pairs of degenerate bands based on two different quasi-particle configurations have been identified in this nucleus indicating the first observation of such bands in an odd-A nucleus in A∼190 region and signify the first evidence of multiple chiral bands in a nucleus in this region. The total Routhian surface calculations predict triaxial shapes for both the configurations and thereby, support the experimental observation. The importance of multiple neutron holes in the i13/2 orbital and the stability of shapes for these two configurations have been discussed.

Low-lying isomeric states in Ga80 from the β− decay of Zn80

A new level scheme of 80Ga has been determined. This nucleus was populated following the β− decay of 80Zn at ISOLDE, CERN. The proposed level scheme is significantly different compared to the previously reported one and contains 26 levels up to 3.4 MeV in excitation energy. The present study establishes that the previously identified 1.9-s β− -decaying 6− isomer is the ground state of 80Ga and the 1.3-s β− -decaying 3− isomer lies at an excitation energy of 22.4 keV. A new isomeric level was identified at 707.8 keV and its half-life was measured to be 18.3(5) ns, allowing the 685.4-keV transition de-exciting this state to be assigned anM2 multipolarity. The newly measured spectroscopic observables are compared with shell-model calculations using the jj44bpn and JUN45 interactions.

Shape coexistence in the near-spherical142Sm nucleus

High spin states of 142 Sm have been investigated using the fusion-evaporation reaction 116 Cd ( 31 P, p4n )a t beam energy 148 MeV using the Indian National Gamma Array (INGA). Approximately sixty new gamma transitions have been placed in the proposed level scheme, which has been extended up to ≈12.5 MeV. Several band-like structures including one dipole band and three quadrupole bands have been observed in the proposed level scheme. Lifetimes of several levels in the dipole band and quadrupole bands have been measured using doppler shift attenuation method (DSAM). The deduced B(M1) values for the dipole band have been compared with the semiclassical shears mechanism with the principle axis cranking (SPAC) model, and the dipole band has been interpreted as a magnetic rotational band. Comparisons between the experimental characteristics and cranked Nilsson-Strutinsky (CNS) calculations for the observed quadrupole bands indicate that these bands have been formed on the triaxial deformed shape of 142 Sm.

Signature splitting inversion and backbending in80Rb

High-spin states of ${}^{80}$Rb are studied via the fusion-evaporation reactions ${}^{65}$Cu+${}^{19}$F, ${}^{66}$Zn+${}^{18}$O, and ${}^{68}$Zn+${}^{16}$O with the beam energies of 75 MeV, 76 MeV, and 80 MeV, respectively. Twenty-three states with twenty-eight \ensuremath{\gamma} transitions are added to the previously proposed level scheme, where the second negative-parity band is significantly pushed up to spins of 22${}^{\ensuremath{-}}$ and 15${}^{\ensuremath{-}}$ and two sidebands are built on the known first negative-parity band. Two successive band crossings with frequencies 0.51 MeV and 0.61 MeV in the \ensuremath{\alpha} $=$ 0 branch as well as another one in the \ensuremath{\alpha} $=$ 1 branch of the second negative-parity band are observed. Signature inversions occur in the positive-parity and first negative-parity bands at the spins of 11$\ensuremath{\hbar}$ and 16$\ensuremath{\hbar}$, respectively. The signature splitting is seen obviously in the second negative-parity band, but the signature inversion is not observed. It is also found that the structure of the two negative-parity bands is similar to that of its isotone ${}^{82}$Y. Signature inversion in the positive-parity yrast band with configuration \ensuremath{\pi}${g}_{9/2}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}$ in this nucleus is discussed using the projected shell model.

Observation of new microsecond isomers among fission products from in-flight fission of 345 MeV/nucleon238U

A search for isomeric γ decays among fission fragments from 345 MeV/nucleon 238U has been performed at the RIKEN Nishina Center RI Beam Factory. Fission fragments were selected and identified using the superconducting in-flight separator BigRIPS and were implanted in an aluminum stopper. Delayed γ rays were detected using three clover-type high-purity germanium detectors located at the focal plane within a time window of 20 μs following the implantation. We identified a total of 54 microsecond isomers with half-lives of ∼0.1–10 μs, including the discovery of 18 new isomers in very neutron-rich nuclei: 59Tim, 90Asm, 92Sem, 93Sem, 94Brm, 95Brm, 96Brm, 97Rbm, 108Nbm, 109Mom, 117Rum, 119Rum, 120Rhm, 122Rhm, 121Pdm, 124Pdm, 124Agm, and 126Agm, and obtained a wealth of spectroscopic information such as half-lives, γ-ray energies, γ-ray relative intensities, and γγ coincidences over a wide range of neutron-rich exotic nuclei. Proposed level schemes are presented for 59Tim, 82Gam, 92Brm, 94Brm, 95Brm, 97Rbm, 98Rbm, 108Nbm, 108Zrm, 109Mom, 117Rum, 119Rum, 120Rhm, 122Rhm, 121Pdm, 124Agm, and 125Agm, based on the obtained spectroscopic information and the systematics in neighboring nuclei. The nature of the nuclear isomerism is discussed in relation to the evolution of nuclear structure.13 MoreReceived 10 August 2012DOI:https://doi.org/10.1103/PhysRevC.86.054319©2012 American Physical Society

First observation of excited states of173Hg

The neutron-deficient nucleus 173Hg has been studied following fusion-evaporation reactions. The observation of gamma rays decaying from excited states are reported for the first time and a tentative level scheme is proposed. The proposed level scheme is discussed within the context of the systematics of neighbouring neutron-deficient Hg nuclei. In addition to the gamma-ray spectroscopy, the alpha decay of this nucleus has been measured yielding superior precision to earlier measurements.

Interplay between single-particle and collective excitations in argon isotopes populated by transfer reactions

New γ transitions have been identified in argon isotopes in 40 Ar + 208 Pb multiple transfer reactions by exploiting, in a fragment-γ measurement, the new generation of magnetic spectrometers based on trajectory reconstruction coupled to large γ arrays. The coupling of single-particle degrees of freedom to nuclear vibration quanta was discussed. The interpretation of the newly observed states within a particle-phonon coupling picture was used to consistently follow, via their excitation energies, the evolution of collectivity in odd Ar isotopes. The proposed level schemes are supported by the results of sd-pf shell-model calculations, which have been also employed to evaluate the strength functions of the populated states.

Energy levels in 141Nd from fusion evaporation study

The nucleus 141Nd has been investigated using two different heavy ion fusion evaporation reactions, namely 130Te(16O, 5n) at Elab = 80–85 MeV and 124Sn(24Mg,α3n) at Elab = 107 MeV, and the de-exciting gamma rays were detected using HPGe(GDA) and Clover detector (INGA) arrays, respectively. More than 30 new gamma transitions have been placed in the proposed level scheme, which has been extended up to 9 MeV excitation energy and spin parity values of 45/2−. Spin parity assignments have been made to most of the newly proposed levels. The structure up to approximately 6 MeV excitation energy and spin 31/2− can be explained using the shell model in a truncated basis. The levels with higher spin/energy cannot be described using even the full 50–82 shell, indicating the influence of neutron excitations across the shell gap in this mass region. One M1 band that has been observed is proposed to have a five quasiparticle configuration.

Spectroscopy of exotic 121, 123, 125Ag produced in fragmentation reactions

Excited states in the neutron-rich 121, 123, 125Ag were studied via the fragmentation of a 136Xe beam at 120MeV/nucleon in a thick 9Be target. The levels in 121Ag were populated in the $ \beta$ decay of 121Pd while those assigned to 123, 125Ag were identified via isomer spectroscopy. The transitions identified in 121Ag are consistent with the $ \gamma$ -rays reported in 117, 119Ag . The newly observed transitions were placed in the level schemes of 123, 125Ag based on the analysis of $ \gamma$ - $ \gamma$ coincidences and the systematics. We attribute the onset of isomerism in the 123, 125Ag isotopes to the drop in energy of the negative-parity levels similar to the 5- state in the even-even Cd cores. The proposed level scheme for 125Ag is well described by the NuShellX shell model calculations.

Low-energy states of3181Ga50: Proton structure of the nuclei close toNi78

The \ensuremath{\beta} decay of the neutron-rich ${}_{30}^{81}{\mathrm{Zn}}_{51}$ has been investigated at the PARRNe mass separator at the IPN Orsay. The sources of $^{81}\mathrm{Zn}$ were produced using the ISOL (Isotopic Separation On Line) technique by the fission of ${}^{\mathrm{nat}}$U exposed to the neutron flux produced by the 26-MeV deuteron beam delivered by the MP-Tandem. With \ensuremath{\gamma} and $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence measurements, excited levels were attributed to ${}_{31}^{81}{\mathrm{Ga}}_{50}$ for the first time. A partial decay scheme for $^{81}\mathrm{Zn}$ is proposed. The proposed level scheme is well reproduced by shell model calculations using the most recent effective empirical interaction. We show that the structure of this nucleus is consistent with that of the heavier odd-proton $N=50$ isotones within the assumption of strong proton $Z=28$ and neutron $N=50$ effective shell effects. The observed states can be associated to rather simple and clean configurations of three protons placed in the $1{f}_{5/2}$ and $2{p}_{3/2}$ orbits.

Spectroscopy and Lanthanide Impurity Level Locations in CaGa2 S 4 : Ln3 + ( Ln = Ce , Pr , Tb , Er , Tm )

The emission and excitation spectra of single crystals of doped with and were measured with the aim to determine the location of the lanthanide energy levels relative to the valence and conduction band of the host crystal. By combining energies known for charge transfer bands involving trivalent lanthanides with systematic behavior in 4f-5d transition energies of divalent lanthanides, the level positions of 4f and 5d states for each divalent lanthanide can be drawn relative to the host levels. With similar techniques combined with results on the thermal quenching behavior of emission, the levels for the trivalent lanthanides were constructed. We demonstrate consistency between the proposed level scheme and the spectroscopic information presented here and elsewhere. The scintillation properties of -doped are addressed also. © 2004 The Electrochemical Society. All rights reserved.

Nuclear structure ofGd159

The well deformed atomic nucleus $^{159}\mathrm{Gd}$ was investigated by means of radiative neutron capture and single neutron transfer reactions. Nearly 70 secondary $\ensuremath{\gamma}$ rays from the $(n,\ensuremath{\gamma})$ reaction studied with high-resultion bent-crystal spectrometers at Grenoble are assigned to $^{159}\mathrm{Gd}$. About 200 levels with spin up to $\frac{11}{2}$ are observed in this nucleus below $2.3\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ in $(d,p)$ and $(\mathbf{d},t)$ reactions investigated at the Tandem Van de Graaff accelerator in Garching using unpolarized $(18\phantom{\rule{0.3em}{0ex}}\mathrm{MeV})$ and polarized $(22\phantom{\rule{0.3em}{0ex}}\mathrm{MeV})$ deuteron beams, respectively. The proposed level scheme for this nucleus is arranged into 21 rotational bands. Experimentally observed levels are interpreted using predictions obtained within the quasiparticle-phonon model and the quasiparticle-rotor approach for a well deformed nucleus.

Experimental study of nuclear structure ofMo91at high spin

The high spin structure of $^{91}\mathrm{Mo}$ with neutron and proton number close to magicity has been investigated using the $^{63}\mathrm{Cu}(^{31}\mathrm{P},\mathit{xnyp})$ reaction at an incident beam energy of $125\phantom{\rule{0.3em}{0ex}}\text{MeV}$. The level at ${E}_{x}=3811\phantom{\rule{0.3em}{0ex}}\text{keV}$ has been assigned a negative parity based on our polarization measurements. In view of this change, the observed level structure for $^{91}\mathrm{Mo}$ so far does not have any negative parity sequence. More than 30 new transitions were observed and placed in the decay scheme, which has been extended up to spin of $J\ensuremath{\sim}39∕2\ensuremath{\hbar}$ and an excitation energy of ${E}_{x}\ensuremath{\sim}10\phantom{\rule{0.3em}{0ex}}\text{MeV}$. The energy spectrum bears signature of core breaking viz. presence of high energy $({E}_{\ensuremath{\gamma}}\ensuremath{\sim}2\phantom{\rule{0.3em}{0ex}}\text{MeV})$ $\ensuremath{\gamma}$ rays originating due to excitation of nucleons across the shell gaps. The proposed level scheme is compared with large basis spherical shell model calculations. Excitation of protons across $Z=38$ shell dominates the level structure up to moderate spins i.e., $J\ensuremath{\sim}27∕2\ensuremath{\hbar}$. Configurations arising due to excitation of a single $\ensuremath{\nu}{g}_{9∕2}$ across $N=50$ shell gap dominate the higher angular momentum $J\ensuremath{\geqslant}35∕2\ensuremath{\hbar}$ states.

“Complete” high-spin structure of57Co

A comprehensive high-spin decay scheme has been deduced for ${}^{57}\mathrm{Co}$ using the Gammasphere Germanium detector array coupled to the $4\ensuremath{\pi}$ charged-particle detector system Microball. Following the fusion-evaporation reaction of ${}^{28}\mathrm{Si}{(}^{36}\mathrm{Ar},1\ensuremath{\alpha}{3p)}^{57}\mathrm{Co}$ at 136 MeV beam energy about 90 excited states have been observed in ${}^{57}\mathrm{Co},$ which are connected by some 230 $\ensuremath{\gamma}\ensuremath{-}\mathrm{r}\mathrm{a}\mathrm{y}$ transitions. The proposed level scheme reaches 16 MeV excitation energy at a spin of $17\ensuremath{\Elzxh}--18\ensuremath{\Elzxh}.$ With its complexity the level scheme of ${}^{57}\mathrm{Co}$ appears to be ``complete'' up to 1 or 2 MeV above the yrast line. This aspect is further investigated through a comparison of the data with spherical shell-model calculations.

Study of the neutron-rich nuclei with N=21, 35Si and 33Mg, by beta decay of 35Al and 33Na

The first information on the level structure of the N=21 nuclei, 35Si and 33Mg, has been obtained by the beta decay study of 35Al and 33Na, produced by fragmentation of an UC target with 1.4 GeV protons at CERN/ISOLDE. The experimental technique involved β– γ, β– γ– γ, and β–n– γ coincidences, neutron spectra being obtained by time of flight measurements. Gamma detection was made either using large Ge counters or small BaF 2 scintillators (for lifetime measurements). In the case of the 35Al decay, ( T 1/2=41.6(2.2) ms), a simple structure has been found for the level scheme of 35Si ( Z=14, N=21) which has been interpreted with the level sequence : 7/2 −, 3/2 − and 3/2 + corresponding respectively to the ground state and the states at 910 and 974 keV. The life-time of the 974 keV [ T 1/2=5.9(6) ns] is found consistent with the proposed level scheme and multipolarities. The investigation of the N=21, very neutron rich isotones, has been carried on with the study of 33Mg resulting from the 33Na decay, ( T 1/2=8.0(6) ms). In this case also, a level scheme could be obtained for the first time, with 5 bound states in 32Mg and 31Mg levels, populated in the 1n and 2n channels. These results are compared with sd–fp shell model calculations which give a fair account of the Gamow–Teller distribution and a reasonable explanation of the lowest levels with predominant contribution of 1p–1h and 2p–2h excitations.

Decay of [formula omitted

The γ-ray spectrum of 72 Ge following the β − decay of 72 Ga has been studied using both single and gamma–gamma coincidence spectroscopy techniques. The energies and intensities of 110 γ-rays have been determined, 26 of them were observed for the first time and 20 have been confirmed. Of the total number of γ-rays observed, 95 have been placed in a proposed level scheme containing 31 levels. This includes five new levels at 2303, 2694, 3067, 3097 and 3420 keV.

Yrast states of the proton drip line nucleus106Sb

Yrast states of Sb-106 have been investigated in the Fe-54(Ni-58, alpha pn) reaction using in-beam gamma-spectroscopic methods and in the Cr-50(Ni-58,pn) reaction performing delayed gamma and conversion electron studies. A new isomeric state was found at 103 keV with t(1/2) = 232(21) ns. The number of start's and transitions in the proposed level scheme have been doubled. The experimental results are discussed within the framework of the shell model. [S0556-2813(99)08502-7].

Band structure in104Ag

The level structure of104Ag has been studied through the103Rh (α, 3nγ) reaction at Eα=40 and 45 MeV. The principal features of the proposed level scheme are in agreement with those obtained earlier through heavy ion reaction. Two quasiparttcle-plus-rotor model calculation has been performed, and the results are compared with experimental data.