Neutron Particle-hole States Research Articles

One-phonon octupole vibrational states in 136Xe, 137Cs, 138Ba, 140Ce and 142Nd with N = 82

Excited high spin states in 136Xe, 137Cs, 138Ba, 140Ce and 142Nd with N = 82 are reorganized and interpreted in terms of the weak coupling mode of an octupole 3− phonon. Nearly identical sequences of levels with ΔI = 3 and Δπ = yes built on 17/2+ and 23/2− states are found, for the first time, up to 29/2+ and 35/2−, respectively, for 22 states of 137Cs . Also, nearly identical sequences of levels with ΔI = 3 and Δπ = yes built on the 6+ and 9− states are found, for the first time, up to 14+ and 17−, respectively, for 18 states of 136Xe, up to 14+ and 17−, respectively, for 24 states of 138Ba and up to 11+ and 14−, respectively, for 14 states of 140Ce. New spins and parities are assigned, tentatively, to the high spin states of these nuclei based on the weak coupling mode of an octupole 3− phonon. The weak coupling of an octupole 3− phonon needs to be considered when single particle configurations are assigned to high spin states. Neutron particle-hole states (νh 11/2 −1 f 7/2 +1 ) with weak coupling of an octupole 3− phonon are proposed, for the first time. The νh 11/2 −1 f 7/2 +1 excitation energies (E ext(1p1h)) are nearly constant with increasing of Z. One-phonon excited states in 136Xe, 137Cs, 138Ba and 140Ce have the stretched weak coupling configurations of ΔI = 3. But one-phonon excited states in 142Nd show the non-stretched weak coupling configurations of an octupole phonon with ΔI = 3 and 2.

Thei11/2f5/2andi11/2p3/2neutron particle-hole multiplets inPb208

Inelastic proton scattering via isobaric analog resonances allows derivation of rather complete information about neutron particle-hole states. We applied this method to the doubly-magic nucleus $^{208}\mathrm{Pb}$ by measuring angular distributions of the reaction $^{208}\mathrm{Pb}$($p,{p}^{'}$) on top of the isobaric analog resonances in $^{209}\mathrm{Bi}$ with the Q3D magnetic spectrograph at M\"unchen. We identify the six states of the ${i}_{11/2}{f}_{5/2}$ multiplet and the four states of the ${i}_{11/2}{p}_{3/2}$ multiplet in the energy range $4.6\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}<{E}_{x}<5.3$ MeV. Firm spin assignments for the 10 states are given, most of them new. Additional measurements of the reaction $^{207}\mathrm{Pb}$($d,p$) confirm the assignments. A new state at ${E}_{x}=5239$ keV has a dominant proton particle-hole structure with spin ${4}^{\ensuremath{-}}$.

The γ-decay of particle-hole states in 208Pb using the Euroball Cluster detector

Abstract Neutron particle-hole states in the doubly magic nucleus 208 Pb were investigated using a Euroball Cluster detector and five usual HPGe detectors at the Osiris cube spectrometer in Cologne. 126 γ-ray transitions with energies up to 7.2 MeV could be detected 14 for those for the first time. The states were excited with the 208 Pb( p , p ' γ ) 208 Pb reaction via isobaric analogue resonances in 209 Bi at E p = 16.5, 17, 17.45, 17.5 and 18.5 MeV and though the subcoulomb 207 Pb( d , pγ ) 208 Pb reaction at E d = 10 MeV. For most of the excited states assignments for the particle and/or the hole component of the configuration could be made, 22 of these are new.

Particle-hole states in 138Ba

The thermal-neutron-capture gamma rays and γγ-coincidences were measured by means of Ge detectors. Using primary and secondary (n, γ) data, the level scheme of 138Ba was established with 63 levels up to an excitation energy of 5 MeV. The level energies and (d, p) transfer data were compared with model predictions of the interacting boson-fermion-fermion model. As shown, this model provides a basic understanding of the neutron particle-hole states of 138Ba in the energy range of 3.5 – 5.0 MeV.

Systematics of the pygmy resonance in keV neutron capture γ-ray spectra of nuclei with N ≈ 82–126

We have measured capture gamma-ray spectra of Pr, Tb, Ho, Lu, Ta and Au at neutron energies of 10 to 800 keV with an anti-Compton NaI(Tl) detector, employing a time-of-flight technique. An anomalous bump, so-called the pygmy resonance, was observed in all these spectra. Remarkable features of the pygmy resonance were found to be that the resonance energy and the electric-dipole strength exhausted in the resonance increase with neutron number but these quantities decrease precipitously around the neutron magic number of N = 82. Comparison with theoretical calculations suggests that the pygmy resonance is mainly made up of neutron particle-hole states decoupled from the giant electric-dipole resonance and is excited in a collective mode.

Interaction between neutron particle-hole and octupole core-coupled states in N = 83 nuclei

We have studied both experimentally and theoretically the interplay between the particle octupole core-coupled states ( Jπ = 1 2 +,…, 13 2 + ) and the low-lying neutron 2p-1h intruder excitations with the neutron hole moving in the s 1 2 −1 , 2 d 3 2 −1 , and 1 h 11 2 −1 orbitals in odd-mass N = 83 nuclei.

Neutron particle-hole multiplet states in 90Zr studied by proton inelastic scattering

The ν(g 9/2) −1(d 5/2) multiplet states in 90Zr have been identified using proton inelastic scattering at 65 MeV. The measured angular distributions were compared with microscopic DWBA calculations using simple shell-model wave functions. Remarkable agreement has been obtained for all the unnatural parity states of J π = 3 +, 5 + and 7 +.

The T> GDR and the characteristic decay mode by the (e, p) reaction on 139La and 141Pr

The cross sections and the proton energy distributions of the (e, p) reactions on 139La and 141Pr have been measured around the T > GDR. The energies of the T > GDR have been given as E R = 21.0 MeV in 139La and E R = 20.4 MeV in 141Pr. The decay protons of the T > GDR have been studied. The proton groups which leave the residual nucleus in the neutron particle-hole states have been clearly seen in the same energy regions as the decay protons emitted through the low-lying IAR.

Electric dipole and quadrupole ground state transitions inBa138fromBa138(γ,γ) andBa138(γ,γ′)

Twelve ground state transitions up to about 5 MeV have been observed by the resonant scattering of bremsstrahlung from natural barium. Six of the first seven lines are from ${2}^{+}$ states in $^{138}\mathrm{Ba}$ as evidenced by the angular distribution measurements and the correspondence of the energies with known levels in $^{138}\mathrm{Ba}$. Presumably these arise from proton configurations. Of the remaining five lines four have distributions expected for spin 1 levels. The linear polarization of the scattered radiation for the first of these, at 4027 keV, suggests a negative parity. It is likely that this state is derived from the superposition of the one phonon quadrupole and octupole transitions in $^{138}\mathrm{Ba}$. Comparison with the results of other studies indicates that the other three lines are from neutron particle-hole states in $^{138}\mathrm{Ba}$. Widths in terms of the ground state branching ratios and the partial widths for decays to the ground state are given for the identified levels.NUCLEAR REACTIONS $^{138}\mathrm{Ba}$ ($\ensuremath{\gamma},\ensuremath{\gamma}$), ($\ensuremath{\gamma},{\ensuremath{\gamma}}^{\ensuremath{'}}$); bremsstrahlung $E=1.5\ensuremath{-}5.1$ MeV; measured $\ensuremath{\sigma}$ (96\ifmmode^\circ\else\textdegree\fi{}) and $\ensuremath{\sigma}$ (126\ifmmode^\circ\else\textdegree\fi{}), $\mathrm{LP}$; deduced $J$, $\ensuremath{\pi}$, $\ensuremath{\Gamma}$. Natural targets.

Decay of mass-separatedI136to levels in theN=82nucleusXe136including neutron particle-hole states

A total of 142 $\ensuremath{\gamma}$ rays were observed in the decay of the 45- and 85-sec isomers of $^{136}\mathrm{I}$ using an on-line isotope separator system. Of these, 116 were placed in a level scheme for $^{136}\mathrm{Xe}$ consisting of 50 excited levels up to 6624 keV using results from Ge(Li) $\ensuremath{\gamma}$ singles and $\ensuremath{\gamma}\ensuremath{\gamma}$-coincidence measurements. Our results are compared with results from earlier decay and reaction experiments, and the levels below 2.8 MeV are compared with predictions of recent shell-model calculations. Strong $\ensuremath{\beta}$ population was observed to states above 3.5 MeV which are interpreted as neutron particle-hole states.RADIOACTIVITY $^{136}\mathrm{I}$ [from $^{235}\mathrm{U}(n, f)$]; measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, $\ensuremath{\gamma}\ensuremath{\gamma}$-coin, Ge(Li) detectors; $^{136}\mathrm{Xe}$ deduced levels, $J$, $\ensuremath{\pi}$, $log\mathrm{ft}$. Mass-separated $^{136}\mathrm{I}$ activity.

First observation of (s+d)-wave mixing in low-energy elastic neutron scattering

A large (s+d)-wave mixing is observed in the 256 KeV ( J π = 1 −) resonance in 207Pb + n. A possible interpretation in terms of neutron particle-hole states is discussed.

Photoproton reactions on 208Pb

Photoproton energy distributions have been measured for the (e, e′p) reaction at a number of bombarding energies. The results are used to obtain the (e, e′p) cross sections and isochromats. The (e, e′p) cross sections are analyzed to get the (γ, p) cross sections. The results and (γ, p) cross sections show a strong resonance around 25.0 MeV, whose energy and integrated cross section agree well with theory for IAR. Proton spectra emitted through the IAR are extracted from the photoproton spectra and also from the isochromats. Strong proton groups are found at around 15.3 MeV and 11 MeV corresponding to the h 11 2 proton hole state at 1.3 MeV and also neutron particle-hole states around 6 MeV in the residual nucleus. The result is in good agreement with estimates obtained from proton scattering on 208Pb, showing the configuration of the IAR states.

Sr87(d,p)Sr88reaction

Neutron particle-hole states in $^{88}\mathrm{Sr}$ have been studied by means of the reaction $^{87}\mathrm{Sr}(d,p)^{88}\mathrm{Sr}$ at ${E}_{d}=12$ MeV. It has been determined that the earlier reported transitions to presumed states at 4744 and 5780 keV in $^{88}\mathrm{Sr}$ arise mainly from transition to the ground state and the first excited state in $^{89}\mathrm{Sr}$. Spectroscopic strengths for states of the multiplets [${{g}_{\frac{9}{2}}}^{\ensuremath{-}1}{d}_{\frac{5}{2}}$] and [${{g}_{\frac{9}{2}}}^{\ensuremath{-}1}{s}_{\frac{1}{2}}$] have been determined by detailed distorted-wave Born-approximation analysis. ${J}^{\ensuremath{\pi}}$ assignments are suggested on the basis of sum rules and comparison with other experiments. Matrix elements for two-particle effective interactions are derived.NUCLEAR REACTIONS $^{87}\mathrm{Sr}(d,p)$, $E=12$ MeV; measured $\ensuremath{\sigma}(\ensuremath{\theta})$ deduced level energies, ${J}^{\ensuremath{\pi}}$; deduced two body matrix elements; enriched targets.

Generalized neutron particle-hole states in an extended unified model

Abstract Negative-parity levels in the doubly even N = 82, Z nuclei, with 3.0 MeV ⪅ E x ⪅ 6.0 MeV are described in an extended unified-model approach, where neutron hole states in the Z = 50, N = 82 closed shell core, (i.e. 2 d 3 2 −1 ,3 s S 1 2 −1 ,2 d 5 2 −1 ,1 g 7 2 −1 ) are coupled to the low-lying levels ( E x ⪅ 2.0 MeV) of the odd-neutron N = 83, Z nuclei. This particular configuration space of generalized neutron particle-hole states (GNPH) is particularly suited for describing negative-parity levels obtained in proton inelastic scattering through isobaric analogue resonances (IAR), corresponding to the N = 83, Z low-lying nuclear levels. Level schemes as well as partial decay widths and angular distributions are calculated and compared extensively with the available experimental data. Also spectroscopic factors, as well as wave functions, deduced from the experimental results are studied in detail. Thus in the cases of 136 Xe, 138 Ba, 140 Ce, 142 Nd and 144 Sm, some of the important neutron particle-hole configurations can uniquely be determined in the energy region 3.0 MeV ⪅ E x ⪅ 6.0 MeV.

Energy levels in 142Nd

The excited states of 142Nd were studied by means of the decay of 40 sec 142Pm and the 142Nd(p, p') reaction via isobaric analog resonances. Approximately sixty levels of 142Nd were observed below 5.3 MeV excitation, including several neutron particle-hole states excited strongly in (p, p') at f 7 2 , p 3 2 , p 1 2 and f 5 2 analog resonances. We have collected together all known energy levels in 142Nd and have proposed J π assignments for 22 excited states. We have also compared the experimental level spectrum (positive-parity states only) with a calculated one based on the shell model.

Generalized neutron particle-hole states in an extended unified-model description

Negative-parity levels for the even-even N = 82 nuclei, in the energy region 3.5 MeV<Ex<5.5 MeV, are described in an extended unified model, in terms of neutron hole states coupled to the low-lying states of the N = 83 nuclei. These states are selectively fed in the inelastic proton scattering through isobaric analogue resonances of the low-lying N = 83 levels. Application is made to the energy spectrum calculation of 140Ce and the partial decay widths to levels in 140Ce.

Analogue states of 88Sr and the 87Sr(p, p) 87Sr reaction

The isobaric-analogue states of levels in 83Sr have been studied by elastic proton scattering from 87Sr for bombarding energies E p = 4.5 to 7.5 MeV. Several resonances were observed whose spacings and strengths match well to neutron particle-hole states known from the 87Sr(d, p) 88Sr reaction. Simple Breit-Wigner curves have been compared with the data. The energetic and spectroscopic information so obtained has been compared with that from the 87Sr(d, p) 88Sr reaction. No inelastic transitions in the range 0-3 MeV excitation in 87Sr were detected from on- and off-resonance magnetic spectrograph exposures also taken here.

Generalized neutron particle-hole states in the N = 82 isotone 142Nd

Angular distributions for the inelastic proton decay of the two lowest isobaric analogue resonances in 143Pm ( J π = 7 2 − , 3 2 − ) have been measured. Proton decay widths and excitation energies for levels in 142Nd between E x = 3 MeV and 5 MeV are deduced. Most of the observed levels can be interpreted as generalized neutron particle-hole (GNPH) states, a concept to which physical significance has been given by a similar experiment on 140Ce. Level spacings of the GNPH states as well as partial widths and angular distributions of decay protons from corresponding J π = 7 2 − and 3 2 − resonances are found similar for the different N = 82 isotones. The wave functions of four prominent states in 142Nd are determined in terms of GNPH configurations | lj −1, J π 〉 with lj = d 3 2 , s 1 2 , d 5 2 and J π = 7 2 − and 3 2 − . The wave functions of these states are similar to those of corresponding states in 140Ce. The spin splitting of the lowest GNPH configuration ¦d 3 2 − , 7 2 −ĭs identical for both N = 82 nuclei within the uncertainties of the analysis. This shows that the interaction among GNPH configurations depends only weakly on the number of protons. This fact is used to assign spins 1 − and 2 − to states containing appreciable amounts of the configuration | s 1 2 − , 3 2 − 〉

Spins of generalized neutron particle-hole states in 140Ce with excitation energies above Ex=4 MeV

Spins are assigned to states in 140Ce observed in the proton decay of resonances which are the isobaric analogues of the first (J π= 3 2 −) , second (J π= 1 2 −) and fifth (J π= 5 2 −) excited states in 141Ce. Spins 2 −, 1 −, 2 −, 2 − and 1 − are assigned to the states at E x = 4.158, 4.182, 4.580, 4.748 and 4.77 MeV in 140Ce, respectively. The states at E x = 5.026, 5.196, 5.424 and 5.466 MeV are shown to have spins 2 − or 3 −. The assignments are based on the assumption that only the generalized neutron particle-hole configurations | d 3 2 −1⊗ 141 Ce(Jβ)〉 and | s 1 2 −1 ⊗ 141 Ce (Jβ)〉 contribute to the proton widths measured on the resonance Jβ.

Particle-hole and particle-particle interactions in the mass-90 region

States of ( g 9 2 ν) −1( d 5 2 ) aand ( g 9 2 π)( d 5 2 ν) are calculated using realistic inyeractions with inclusion of core polarization. Comparison is made to experimentally observed neutron particle-hole states in 88Sr and 90Zr ant to particle-particle states in 90Y and 92Nb.