The level scheme of91Nb from the reaction90Zr (p, γ)91Nb

The level scheme of⁹¹Nb has been investigated with the reaction⁹⁰Zr(p, γ)⁹¹Nb. Proton energies between 3.0 and 7.2 MeV were used. The γ spectra were taken with Ge(Li) detectors. Primary γ transitions to 36 excited states of⁹¹Nb up to 3.8 MeV excitation energy and many secondary γ transitions from the decay of those states were observed, leading to an extension of the known level scheme. The proton binding energy for⁹¹Nb was determined as (5167± 5) keV. Eleven γ transitions in⁹⁰Zr, part of them new, from the competing reaction⁹⁰Zr(p, p′ γ) were also observed.     

Collective and single-particle states at high excitation energy

Damping of high-lying single-particle states was investigated by the study of decay by proton emission from high-lying states in ⁹¹Nb, populated by the ⁹⁰Zr(α, t) reaction at E_α=180 MeV. In addition to decay to the ground state of ⁹⁰Zr, semi-direct decay was observed to the low-lying (2⁺/5^? and 3^?) phonon states, confirming the conclusion from other experiments that phonon states play an important role in the damping process of the single-particle states. Furthermore, the population and decay of isobaric analogue states of ⁹¹Zr, which are located at an excitation energy of about 10–12 MeV in ⁹¹Nb, has been studied in the same reaction.     

Proton pick-up from Mo

The reaction ⁹²Mo(t, α)⁹¹Nb has been carried out at a triton bombarding energy of 12 MeV. Angular distributions of the emitted α-particles were obtained and compared with DWBA predictions. Relative spectroscopic factors were obtained for six low-lying states and are discussed with reference to shell-model calculations.     

Spin-parity assignments for the excited states of 91Nb from the 91Zr(p,nγ)91Nb reaction

The energy levels of ⁹¹Nb were studied by means of the (p, nγ) reaction. The de-excitation γ-rays were observed with a Ge(Li) detector in the proton energy range from 3.25 to 5.51 MeV in steps of about 30 keV. Resonances attributed to isobaric analog states in the compound system ⁹¹Nb were observed in the excitation functions of the de-excitation γ-rays. From an analysis of these analog resonances, a Hauser-Feshbach analysis and the γ-decay scheme, the spin-parities of the levels up to 2792.6 keV (22 levels) were assigned.     

Isomeric ratios in photonuclear reactions of molybdenum isotopes induced by bremsstrahlung in the giant dipole resonance region

We have determined the isomeric ratios of isomeric pairs ^97m,gNb, ^95m,gNb and ^91m,gMo produced in ⁹⁸Mo(γ, p)^97m,gNb, ⁹⁶Mo(γ, p)^95m,gNb and ⁹²Mo(γ, n)^91m,gMo photonuclear reactions in the giant dipole resonance (GDR) region by the activation method. The results were analyzed, discussed and compared with the similar data from literature to examine the role of excitation energy, neutron configuration, channel effect and direct and pre-equilibrium processes in (γ, p) photonuclear reactions. In this work the isomeric ratios for ^97m,gNb from 14 to 19 MeV, for ^195m,gNb from14 to 24 MeV except 20 and 23.5 MeV and for ^91m,gMo at 14 and 15 MeV are the first time measurements.     

The 93Nb(p,d)92Nb reaction at 26.3 MeV

The ⁹³Nb(p, d)⁹²Nb reaction was studied at a proton energy of 26.3 MeV. Angular distributions were obtained for outgoing deuterons to 37 states in ⁹²Nb up to an excitation energy of 4.2 MeV. The results were compared with DWBA calculations to extract l-values and spectroscopic factors. Fourteen previously unobserved l = 1 transitions were measured.     

The Zr(d,n)Nb and Zr(d,n)Nb reactions

The (d, n) reaction on ⁹⁰Zr and ⁹⁶Zr has been studied at 12 MeV deuteron bombarding energy using the neutron time-of-flight technique with an overall neutron time resolution of 1.9 ns. Angular distributions of neutron groups leading to states in ⁹¹Nb and ⁹⁷Nb were measured in the angular range between 15° and 60°. The measured cross sections were analyzed in the framework of the distorted-wave theory of stripping reactions to deduce l-values and proton spectroscopic factors of states in the residual nuclei. The results are compared with the corresponding data available from (³He, d) studies. The fractionation of the single-particle proton states and their centroid energies are determined.     

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

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 $\text{1}\text{2}{}^{\mathrm{?}}\text{(0.48}\text{MeV}\text{)}$ 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.     

Energy levels of92Nb from 92Zr(p,nγ)92Nb

The energy levels of⁹²Nb were studied by means of the⁹²Zr(p, nγ) reaction. The deexcitation γ-rays were observed with a high-resolution Ge(Li) detector in the proton energy range 3.00–4.80 MeV in steps of about 25 keV. Many new excited states of ⁹²Nb were populated by this reaction. Excitation energies up to 1.77 MeV were determined with high precision, and a level scheme of ⁹²Nb is proposed. From a Hauser-Feshbach analysis, the γ-decay scheme and other information, the spin-parities of many levels were assigned.     

Neutron scattering and neutron emission cross sections on 27Al, 93Nb and 209Bi at 7 MeV

Elastic and inelastic neutron scattering and neutron emission at 7 MeV incident energy has been studied for monoisotopic samples of ²⁷Al, ⁹³Nb and ²⁰⁹Bi. Time-of-flight spectra were taken at nine angles between 30° and 140° using the beam-swinger spectrometer. The efficiency of the neutron detectors was maximized using a dynamic bias; low background was obtained throughout the neutron energy detected which correspond to about 6 MeV excitation energy. The data were converted to energy spectra and corrected for sample attenuation, finite geometry and multiple scattering. For unresolved states the data were averaged over 0.5 MeV energy bins. Calculations for elastic and inelastic transitions and for compound and precompound processes are presented.     

Multipolarity of some transitions in the96Zr(p,n γ e)96Nb reaction

The conversion electron andγ-ray spectra of the⁹⁶Zr(p, n γ)⁹⁶Nb reaction were measured with Ge(Li) and superconducting magnet transporter Si(Li) spectrometers respectively, at 4MeV bombarding proton energy. The multipolarities of some transitions were determined and conclusions were drawn on the spins and parities of the excited states of⁹⁶Nb.     

Spin distribution factors for formation of metastable states of 90Y and 91Y through (n,p) reactions over neutron energies 5–15 MeV

The variations in the isomer ratio with the spin distribution factor were studied to obtain the cross-sections for formation of metastable states of ⁹⁰Y and ⁹¹Y nuclei formed respectively through ⁹⁰Zr(n,p)⁹¹Y^m and ⁹¹Zr(n,p)⁹¹Y^m reactions over the neutron energy range 5 to 15 MeV. The theoretical values of the cross-sections could be obtained very close to the respective literature experimental values by varying the spin distribution factor from 1.5 to 2.75. The limiting value of the cross-section was derived from the maximum value of the isomer ratio at that neutron energy, and for this the spin distribution factor was found to vary from 2 to 3.5 over the neutron energies 5 to 15 MeV. Using enriched zirconium targets, cross-sections for formation of ⁹⁰Y^m and ⁹¹Y^m nuclei at 14.8 MeV neutron energy were also measured in the laboratory; the values obtained are 17 ± 2 mb and 22 ± 2 mb respectively for ⁹⁰Y^m and ⁹¹Y^m. Both these values are close to the corresponding limiting cross-sections at 14 MeV neutron energy.     

A proton stripping study of92Nb

Levels up to energies of 4 MeV have been studied with the⁹¹Zr(³He,d)⁹²Nb reaction with an incident particle energy of 25.5 MeV. The product deuterons were analyzed by a split-pole spectrometer. Angular distributions were obtained for many of the transitions and compared with DWBA calculations. The assigned transferl values and spectroscopic factors were used to assign shell model structures to these levels.     

Cluster decay of the high-lying excited states in 14C

A cluster-transfer experiment of ⁹Be(⁹Be,¹⁴C→α+¹⁰Be)α at an incident energy of 45 MeV was carried out in order to investigate the molecular structure in high-lying resonant states in ¹⁴C. This reaction is of extremely large Q-value, making it an excellent case to select the reaction mechanism and the final states in outgoing nuclei. The high-lying resonances in ¹⁴C are reconstructed for three sets of well discriminated final states in ¹⁰Be. The results confirm the previous decay measurements with clearly improved decay-channel selections and also show a new state at 23.5(1) MeV. The resonant states at 22.4(3) and 24.0(3) MeV decay primarily into the typical molecular states at about 6 MeV in ¹⁰Be, indicating a well developed cluster structure in these high-lying states in ¹⁴C. Further measurements of more states of this kind are suggested.     

A broken-pair description of89Y,91Nb and93Tc

The low-energy properties of⁸⁹Y,⁹¹Nb and⁹³Tc are described in a broken-pair model. The shell model space for the protons consists of one major shell and for the neutrons particle-hole states within two major shells are taken into account. The effective interaction is assumed to be a simple Gaussian Serber force, which has proved to be the most successful in adjacent even nuclei. Energy spectra up to about 3 MeV excitation energy and one-nucleon transfer data can be described very well. Also electromagnetic properties can be reproduced rather well if reasonable effective charges are used. No indication for deformed states, as found in Sn nuclei, is observed.     

Band structures in 108In

High spin states in ¹⁰⁸In have been established upto ∼ 8 MeV in excitation energy and to a tentative spin of (23⁻). The data were obtained by in-beam γ-ray spectroscopy using the reaction ⁹³Nb(¹⁹F, p3n)¹⁰⁸In at a beam energy of 86 MeV. Four sequences of dipole bands and a normal rotational band of E2 γ-transitions have been placed in the level scheme. Received: 16 June 1998     

Study of the 133Ba nucleus with the ( \vec d , p) reaction

Excited states in ¹³³Ba were studied with the ¹³²Ba ( $ \vec d $ , p) ¹³³Ba reaction at 24.0MeV, with a polarized deuteron beam using the Munich magnetic spectrograph Q3D. Many unambiguous spin-parity assignments were made up to an excitation energy of 2.2MeV, which allow a detailed comparison with different theoretical calculations, such as the interacting boson-fermion model and the shell model.     

Cross-section measurement for the ~(93)Nb(n,2n)~(92g)Nb reaction at the neutron energy of 14.6 MeV by the AMS method

The cross-section for the~(93)Nb(n,2n)~(92g)Nb reaction has been measured at the neutron energy of 14.6 Me V using neutron activation and accelerator mass spectrometry(AMS)determination of the long-lived product nuclide~(92g)Nb.The neutron energy was generated from the D+T neutron source at the China Institute of Atomic Energy(CIAE).The neutron flux was monitored by measuring the activity of~(92m)Nb produced in the competing reaction channel of~(93)Nb(n,2n)~(92m)Nb.At the neutron energy of 14.6 MeV,the~(93)Nb(n,2n)~(92g)Nb reaction cross-section of(736±220)mb was obtained for the first time.     

Absence of proton weak coupling states in93Nb

The reactions⁹³Nb(p, p)⁹³Nb,⁹³Nb(p, n)⁹³Mo, and⁹³Nb(p, p′) through isobaric analog resonances in⁹⁴Mo have been used to study the structure of low-lying⁹³Nb states, specifically the degree to which these states can be described as single protons coupled to the core states of⁹²Zr. Excitation curves were obtained from 5.8 to 7.6 MeV incident proton energy, for eight states in⁹³Nb. Results of this work are compared to results from Coulomb excitation studies,⁹³Nb(n, n′γ),⁹³Nb(d,p),⁹²Zr(³He,d),⁹⁴Mo(d,³He) and other related work.     

Proton and alpha evaporation spectra in low energy 12C and 16O induced reactions

Proton and alpha particle spectra have been measured in the ¹²C+⁹³Nb and ¹²C+⁵⁸Ni reactions at E(¹²C)=40 and 50 MeV and in the ¹⁶O + ⁹³Nb reaction at E(¹⁶O) =75 MeV. The spectra are compared with the statistical model calculations. The shapes of the calculated spectra are in agreement with experimental data except for the alpha spectrum in the ¹²C + ⁹³Nb reaction at 40 MeV. The observed evaporation bump is at ∼2 MeV lower energy compared to the calculated one. This discrepancy could imply alpha particle emission from a deformed configuration before compound nucleus formation at this near Coulomb barrier beam energy.