States In 90Zr Research Articles

Experimental constraints on the γ-ray strength function in 90Zr using partial cross sections of the [formula omitted] reaction

Partial cross sections of the Y89(p,γ)Zr90 reaction have been measured to investigate the γ-ray strength function in the neutron–magic nucleus 90Zr. For five proton energies between Ep=3.65 MeV and Ep=4.70 MeV, partial cross sections for the population of seven discrete states in 90Zr have been determined by means of in-beam γ-ray spectroscopy. Since these γ-ray transitions are dominantly of E1 character, the present measurement allows an access to the low-lying dipole strength in 90Zr. A γ-ray strength function based on the experimental data could be extracted, which is used to describe the total and partial cross sections of this reaction by Hauser–Feshbach calculations successfully. Significant differences with respect to previously measured strength functions from photoabsorption data point towards deviations from the Brink–Axel hypothesis relating the photo-excitation and de-excitation strength functions.

Double folding analysis of 3He elastic and inelastic scattering to low lying states on 90Zr, 116Sn and 208Pb at 270 MeV

The experimental data on elastic and inelastic scattering of 270 MeV 3He particles to several low lying states in 90Zr, 116Sn and 208Pb are analyzed within the double folding model (DFM). Fermi density distribution (FDD) of target nuclei is used to obtain real potentials with different powers. DF results are introduced into a modified DWUCK4 code to calculate the elastic and inelastic scattering cross sections. Two choices of potentials form factors are used; Woods Saxon (WS) and Woods Saxon Squared (WS2) for real potential, while the imaginary part is taken as phenomenological Woods Saxon (PWS) and phenomenological Woods Saxon Squared (PWS2). This comparison provides information about the similarities and differences of the models used in calculations.

Pairing-excitation versus intruder states inNi68andZr90

A discussion on the nature of the 0+ states in 68Ni (Z=28, N=40) is presented and a comparison is made with its valence counterpart 90Zr (Z=40, N=50). Evidence is given for a 0+ proton intruder state at only ~2.2 MeV excitation energy in 68Ni, while the analogous neutron intruder states in 90Zr reside at 4126 keV and 5441 keV. The application of a shell-model description of 0+ intruder states reveals that many pair-scattered neutrons across N=40 have to be involved to explain the low excitation energy of the proton-intruder configuration in 68Ni.

Effect of tensor correlations on Gamow–Teller states in 90Zr and 208Pb

The tensor terms of the Skyrme effective interaction are included in the self-consistent Hartree–Fock plus Random Phase Approximation (HF + RPA) model. The Gamow–Teller (GT) strength function of 90Zr and 208Pb are calculated with and without the tensor terms. The main peaks are moved downwards by about 2 MeV when including the tensor contribution. About 10% of the non-energy weighted sum rule is shifted to the excitation energy region above 30 MeV by the RPA tensor correlations. The contribution of the tensor terms to the energy weighted sum rule is given analytically, and compared to the outcome of RPA.

Neutron transition densities for the 2 + -8 + multiplet of states in 90Zr

The neutron transition densities of the $2^+-8^+$ levels in $^{90}$Zr were extracted in the process of analysing ({\bf p},p') scattering at 400 Mev. Its comparison with the proton transition densities for these levels was undertaken. The radial shapes of the experimental neutron and proton transition densities for each state were found to be different.

Structure of the 11/2 − analog state in 91Nb populated by the 90Zr( α,t) reaction

Decay via proton emission of isobaric analog states (IAS's) in 91Nb was studied using the 90Zr( α, t) reaction at E α =180 MeV. This study provides information about the damping mechanism of these states. Decay to the ground state and low-lying phonon states in 90Zr was observed. The experimental data are compared with theoretical predictions wherein the IAS ‘single-particle’ proton escape widths are calculated in a continuum RPA approach. The branching ratios for decay to the phonon states are explained using a simple model.

Mean field for the p+90Zr system in the energy range −60 MeV<E<+65 MeV and single-particle features of proton states in 90Zr from a dispersive optical-model analysis

Data on the scattering of protons with energies 5 MeV<E<65 MeV by 90Zr nuclei and data on the energies of proton particle and hole levels in the A+1 and A−1 systems with A=90 are analyzed within the dispersive optical model. The parameters of the mean proton field for 90Zr are determined in the energy range −60 MeV<E<+65 MeV. The predicted single-particle features of the levels (root-mean-square radii of orbits, occupation numbers, spread widths, spectroscopic factors, and spectral functions) comply well with experimental data obtained in (d, 3He), (3He, d), (n, d), and (d, n) reactions for levels near the Fermi surface and in (e, e′p) and (p, 2p) reactions for deep levels.

Damping widths of the charge exchange IVQ states in 90Zr

The spreading widths of the isovector quadrupole ΔT z =∓1 components in 90Zr are evaluated in a microscopic model. The coupling among the 1p1h states is described in the framework of a self-consistent Hartree-Fock+charge exchange RPA theory and the coupling between the 1p1h states and 2p2h configurations is obtained within the charge exchange second RPA. The Skyrme III interaction is used in these calculations.

Giant dipole resonances built on excited states in 90Zr through radiative proton capture

We have studied the 89Y(p, γ i ) 90Zr reaction populating the states of 90Zr at 0.0, 1.761, 2.186, 2.321 and 2.743 MeV. The 90° cross sections were measured from E p = 3.7 to 11.5 MeV. The data were analysed by the statistical and direct-semidirect models. Spectroscopic factors of low-lying states in 90Zr were determined.

Investigation of pairing vibration states in 88Sr and 90Zr via the (d, 6Li) reaction and search for α-vibration states

With a 45 MeV deuteron beam the 94Mo(d, 6Li) 90Zr and 92Zr(d, 6Li) 88Sr reactions have been studied to search for α-vibration states in 90Zr and in 88Sr. No evidence is found for such a state in both nuclei with a strength > 5 % than that of the ground state. Strongly excited 0 + states in 88Sr and 90Zr are those also seen in two-nucleon stripping and pickup reactions.

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 +.

Proton orbit sizes and the electric monopole matrix element in 90Zr

The mean square radii of the 1 g 9 2 , 2 p 1 2 and 2 p 3 2 proton orbits in 90Zr have b een measured and used in an evaluation of the E0 matrix element between the two lowest 0 + states in 90Zr. The E0 proton effective charge is deduced to be 1.37±0.23.

Scattering and transfer reactions for 6, 7Li + 90, 91Zr

Abstract Elastic scattering data have been measured for the 7Li + 90Zr, 6Li + 90Zr, and 6Li + 91Zr systems at E(Li) = 34 MeV. Inelastic scattering data for the 7Li + 90Zr and 6Li + 90Zr systems were also measured for the 2+(2.18 MeV) and 3−(2.75 MeV) states in 90Zr and the 1 2 − (0.48 MeV ) state in 7Li. Optical model analyses of the elastic scattering data and DWBA analyses for the states in 90Zr were performed. The deduced deformation lengths for the 2+ state agreed with those extracted in other studies but the deformation length for the 3− state was smaller. The 90Zr(7Li, 6Li)91Zr angular distributions were measured for the 1.21 and 2.03 MeV states and the 2.19 MeV doublet in 91Zr. Also, 90Zr(7Li, 6He)91Nb angular distributions were measured for the ground states, 0.10, 3.41 and 4.82 MeV states in 91Nb. The transitions well matched in angular momentum were described by finite-range DWBA calculations, while other transitions displayed the same phase problems seen with heavier ions. The extracted spectroscopic information was consistent with the results of other reaction studies. At the present energy, it was not possible to determine whether the l = 1 phase problem that occurs for heavy-ion single-nucleon transfer reactions on 2s-1d shell nuclei occurs in 91Zr also.

Magnetic hyperfine fields of Zr in nickel and iron measured by the DPAD method

The magnetic hyperfine fields of Zr in nickel and iron were measured by the DPAD method. Using the 8+ isomeric states in90Zr and88Zr these fields were found to beHhf(ZrNi)=−4.65(10) T andHhf(ZrFe)=−27.4(4) T, respectively.

Inelastic scattering of 40 MeV polarized protons exciting the low-lying 2 + states in 90Zr and 92Zr

Cross sections and analyzing powers for 40 MeV polarized protons from the low-lying 2 + states in 90Zr and 92Zr have been measured. Very good agreement has been obtained with the coupled-channels collective model using the full Thomas deformed spin-orbit term. The microscopic model including core polarization also gives an excellent description of these states, in contrast to the situation at lower energies where this model was unable to reproduce the data.

Magnetic moments of N = 50 isotones and proton core polarization

Pulsed heavy-ion beams of 4He, 6Li, 32S and 35C1 have been used to populate isomeric states in N = 50 nuclei having a closed neutron shell and a rather pure ( p n 1 2 g m 9 2 ) proton configuration. The g-factors of the 3.4 μs 17 2 − state in 91Nb, the 9.3 ns 11 − state in 92Mo, the 10.1 μs 17 2 in 93Tc, the 65.5 ns 6 + state and the 68 μs 8 + state in 94Ru were measured for the first time and those of 8 + states in 90Zr and in 92Mo were remeasured with improved accuracy. The g-factors increase by (4.2 ± 0.8)% as the p 1 2 proton subshell is filled and decrease by (3.5 ± 1.4)% as the number of protons in the g 9 2 shell increases from two to four. Calculations that take core polarization into account in first-order perturbation theory explain quantitatively the observed magnetic moments. One-pion exchange current contributions have also been calculated.

Elastic and inelastic scattering of 30 MeV polarized protons from 90Zr, 92Zr, and 92Mo

Analyzing powers and cross sections have been measured for elastic and inelastic scattering of 30 MeV polarized protons from 90Zr, 92Zr, and 92Mo. The experimental results are analyzed in terms of the coupled-channels formalism using the vibrational model. The best fits for the analyzing power for all the nuclei are obtained by using the full Thomas form for the spin–orbit potential. These calculations give a very good description for both the cross sections and the analyzing powers of the low-lying 2+, 3−, 5−, and 4+ states in 90Zr, 92Zr, and 92Mo. Only a small increase of the spin–orbit deformation over the central deformation (βLS/βcentral = 1.5) is needed to reproduce the data; this is contrary to the situation at lower energy where a large increase of this ratio was required (Raynal). Some differences between the 90Zr–92Mo data (which are similar) and the 92Zr data have also been observed; this is, however, in agreement with previous results at lower energy. Microscopic model calculations with tensor and spin–orbit components included in the projectile–target interaction (real interaction), and with an exact treatment of 'knock-on' exchange, have also been performed for the 2+ states in these nuclei. These calculations give a very good agreement with the cross sections but a rather poor agreement with the analyzing powers even when a complex interaction is used.

The low-lying spectrum and some E2 transitions of90Zr in the light of a semi-phenomenological approach

A recent shell-model calculation of the low-lying even parity states of 90Zr, using a two-particle-two-hole basis, has predicted an overdepressed ground state. A phenomenological parameter S is introduced to reduce the strong (0g92/)2 mod Veff mod (0f-1p)2) matrix elements, which probably cause this large energy depression. A suitable value of S gives good agreement between theory and experiment, both for the energy spectrum and the E2 transition rates.

Formation Cross Sections of Zirconium-90m and Lead-207m with Fast Neutrons

Abstract The cross sections for the formation of the metastable states of 90Zr, (σ zr), for neutron energy of 14.8 MeV, and that of 207Pb, (σ pb,), for neutron energies from 4.1 to 5.2 MeV have been measured and the results are reported. The experimentally determined value of the cross section for the former is 700±94mb, while for the latter, the cross section increases from 316 + 44 mb to 788±110 mb. The cross section ratio, σpb/σZr, is also studied, which is found to vary from 1.87 to 2.18 for neutron energies from 14.8 to 18.2 MeV respectively. The equality in the half-lives of the metastable states of 90Zr and 207Pb is exploited in the present measurements, which enabled comparative evaluation of the cross sections. Natural samples of zirconium and lead were irradiated simultaneously and the x-rays were measured off-line by a 55 cm3 Ge(Li) detector. Cyclic activation process was adopted to improve the counting statistics. The overall accuracy achieved in the measurements is about 10%.

Inelastic scattering of electrons for90Zr

The states of 90Zr up to 5.8 MeV excitation energy have been studied by (e, e') in the momentum transfer range from 0.29 to 1.07 fm-1. Ground state transition probabilities and transition radii were obtained for the levels excited. Previously published electron scattering data on 90Zr are included in the extraction of these parameters. A comparison of results is made with the model independent measurements of the ( gamma , gamma ') reaction for the 2+ states. Wherever possible, the results for the electromagnetic transition rates are compared with the iso-scalar transition rates and those obtained form (p, p') reactions. Theoretical calculations are seen to be inadequate to describe the strength of the transitions observed in the present experiment.