Energy levels of 92Nb and 94Tc from 92Zr, 94Mo(p,nγ)92Nb, 94Tc

The γ-decays of the energy levels of ⁹²Nb and ⁹⁴Tc were measured following the ⁹²Zr(p, n)⁹²Nb and ⁹⁴Mo(p, n)⁹⁴Tc reactions. For ⁹²Nb the γ-ray thresholds were measured and a detailed excitation function was obtained near the ⁹³Zr ground-state isobaric analog resonance. Also, γ-γ coincidence measurements with two Ge(Li) detectors were made for both ⁹²Nb and ⁹⁴Tc. The coincidence measurements determined ten energy levels in ⁹²Nb and two levels in ⁹⁴Tc. A comparison with particle transfer reactions is used to elucidate the structure of ⁹²Nb levels observed here but not seen in the transfer reactions.     

Gamma decay of93Mo states from92Mo (d,pγ) and93Tc β-decay

The decay scheme of the fragmented single neutron states of93Mo up to 3.2 MeV excitation energy is obtained from a⁹²Mo(d,pγ)⁹³Mo coincidence experiment. The total γ-spectrum from⁹²Mo+d shows additional strong γ-decays following the β-decay of⁹³Tc produced by the (d, n) reaction. The decay scheme is discussed in the frame of the particle-core coupling model. The important role of 2⁺ core excited components inE2 andM1 transitions between states with different angular momentum of the single particle component is pointed out.     

High-spin states in89Nb,88Zr and88Nb with a shell-model description of theN=48 andN=47 nuclei

The reactions⁸⁹Y(α,4nγ),⁸⁹Y(α,p4nγ) and⁸⁹Y(α,5nγ) were used to populate high-spin states in, respectively,⁸⁹Nb,⁸⁸Zr and the previously unstudied nucleus⁸⁸Nb. These states were deduced via in-beam gamma-ray spectroscopy. The results of a shell-model study ofN=48⁸⁸Zr,⁹⁰Mo,⁸⁷Y,⁸⁹Nb andN=47⁸⁷Zr,⁸⁸Nb nuclei are compared to experiment.     

208Pb(p, α)205Tl reaction at 16.475 MeV

The (p, α) reaction was studied on a²⁰⁸Pb target at 16.475 MeV. Nineteen states were observed in²⁰⁵Tl, up to 3.6 MeV in excitation. Angular distributions were obtained for five strong proton-hole transitions, and DWBA fits made to determinelj values. Results are compared with previous²⁰⁶Pb(t, α)²⁰⁵Tl,²⁰⁶Pb(d,³He)²⁰⁵Tl,²⁰⁵Tl(p, p′), and²⁰⁵Tl(n, n′) work.     

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.     

High-spin states in the isotones 89Zr, 91Mo and 93Ru populated in α-particle-induced reactions

The reactions (α, 3nγ) and (α, α′nγ) on ⁸⁸Sr, ⁹⁰Zr and ⁹²Mo were used to populate excited states in ⁸⁹Zr, ⁹¹Mo and ⁹³Ru. The de-excitation of these states was studied by in-beam γ-ray spectroscopy. The short-lived radioactivity of the ⁹²Mo target was measured in order to study the decay of ⁹³Ru. Many new levels were observed, particularly in ⁹¹Mo. They are interpreted as due to the coupling of a $\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ neutron hole with known excited states in ⁹⁰Zr, ⁹²Mo and ⁹⁴Ru.     

Gamow-teller strength distribution in the vicinity of A = 90: (I). Schematic calculation of GT strength in 90, 92, 94Nb

The distributions of Gamow-Teller strength in ^{90, 92, 94}Nb have been calculated utilizing the so-called GT force in the random phase approximation. For ⁹⁰Nb the calculated distribution is in striking agreement with that part of the ⁹⁰Zr(p, n) excitation function leading to 1⁺ excitations in ⁹⁰Nb and qualitative agreement is demonstrated for data from the reactions ^{92, 94}Zr(p, n). Some 25 % of the GT strength is found to lie well below the structureless giant resonance proposed by Ikeda et al. The implications of this result to the β-decay properties of neutron rich nuclei near A = 90 are discussed.     

Role of thermal and photobeta decays in processes of nucleosynthesis of problematic p nuclei of 113In, 115Sn, 92,94Mo, and 96,98Ru in massive stars

The temperature dependence of the rates of ¹¹³Cd →¹¹³In, ¹¹⁵In →¹¹⁵Sn, ⁹²Zr→⁹²Nb →⁹²Mo, ⁹⁴Zr→⁹⁴Nb →⁹⁴Mo, ⁹⁶Mo →⁹⁶Tc→⁹⁶Ru, and ⁹⁸Mo→⁹⁸Tc→⁹⁸Ru thermal beta transitions was studied at temperatures of massive-star matter in the range of 1 × 10⁸–6 × 10⁹ K. These decays are the possible channel of synthesis of the p nuclei of ¹¹³In, ¹¹⁵Sn, ⁹²,⁹⁴Mo, and ⁹⁶,⁹⁸Ru. The abundances of these nuclei present a challenge for models that study the explosivemechanism of synthesis. The contribution of photobeta decay to the synthesis of the aforementioned p nuclei was estimated. It was shown that the channel of thermal beta decay for ¹¹³In, ¹¹⁵Sn, ⁹⁴Mo, and ⁹⁸Ru p nuclei and the channel of photobeta decay for the ⁹⁶Mo p nucleus could be efficient at the high-temperature quasiequilibrium stage of massive-star evolution.     

Study of the excited 0+ states through conversion electron spectroscopy of neutron rich Zr and Mo fission products

A windowless Si(Li) electron detector has been used in conjunction with the gas filled fission product separator JOSEF to study totally converted transitions in Zr and Mo isotopes. The existence of twoβ-decay modes in⁹⁶Y,⁹⁸Y and¹⁰⁰Nb is confirmed. The half-lives of theβ-decaying levels feeding O ₂ ⁺ states in⁹⁶Zr and⁹⁸Zr are 6.0 ± 0.4 sec and 0.60±0.05 sec respectively. A search for other first excited O ₂ ⁺ states shows that no such states are apparent in¹⁰⁰Zr and¹⁰⁴Mo.     

The excitation functions and Isomer ratios for neutron-induced reactions on Mo and Zr

Absolute cross sections of the reactions ⁹²Mo(n, 2n)^91m,91gMo, ⁹²Mo(n, p)⁹²Nb and ⁹²Mo(n, α)^{89m, 89g}Zr, relative cross sections of the reaction ⁹⁰Zr(n, 2n) ^89mZr and isomer ratios of the ⁹⁰Zr(n, 2n) reaction have been measured in the neutron energy range 13–15 MeV. The results for the (n, 2n) reactions are in good agreement with those of the previous studies. The present results for the (n, p) and (n, α) reactions are in disagreement with the previous works. The experimental data are analysed by the statistical model to determine the level-density parameter a, the moment of inertia ? and the strength of the γ-ray transition S_l in order to simultaneously reproduce the experimental data on the excitation function and the isomer ratio in the (n, 2n) reaction. The γ-ray competition, the yrast level and the experimental information on the excited levels of the residual nucleus in the (n, 2n) reaction are taken into account. The obtained values of a, ? and S_l are consistent with those deduced from other types of nuclear data.     

Nucleon scattering analysis from90,92,594Zr and isospin decomposition of transition matrix elements for low-lying collective transitions

Simultaneous analysis of neutron and proton inelastic scattering to low-lying collective states in^{90, 92, 94}Zr are used to derive an isospin decomposition of the corresponding transition matrix elements. The deduced (M _n/M_p) ratios for the strongest transitions are in sharp disagreement with values derived from Coulomb-nuclear interference observed in 35.4 MeV inelastic α-scattering from even Zr isotopes.     

Forward peaking of near Coulomb energy protons in (n,p) reactions at 14.1 MeV

We apply a modified statistical model of compound nucleus reactions to analyse low energy proton angular distributions from the ⁹³Nb(n, p), ^natAg(n, p) and ^natIn(n, p) reactions at E_n=14.1 MeV. The forward peaking at the maximum of the proton evaporation spectrum at E _p = 6–8 MeV is reproduced and interpreted as an indication of the decay of thermalized-nonequilibrated nuclear states.     

States in95Mo and99Mo populated in the (3He, α) reaction

The (³He,α) reaction on⁹⁶Mo and¹⁰⁰Mo targets has been studied at a bombarding energy of 18 MeV. Thel _n transfer assignments have been made on the basis of angular distribution patterns and on an analysis of the ratios of the experimental and theoretical cross-sections of (³He,α) and (d, t) reactions data leading to the same final states. New states are observed in⁹⁵Mo at 3373 keV (9/2⁺); spin and parity assignments are made to levels in⁹⁹Mo at 1621 keV 7/2⁺ (9/2⁺), 1778 keV (5/2^?) and 2078 keV (11/2^?).     

Identification of mixed-symmetry states in an odd-mass nearly spherical nucleus

The low-spin structure of 93Nb has been studied using the (n,n'gamma) reaction at neutron energies ranging from 1.5 to 3 MeV and the 94Zr(p,2ngamma)93Nb reaction at bombarding energies from 11.5 to 19 MeV. States at 1779.7 and 1840.6 keV, respectively, are proposed as mixed-symmetry states associated with the pi2p(1/2)-1x(2(1),MS+,94Mo) coupling. These assignments are derived from the observed M1 and E2 transition strengths to the 2p(1/2)-1x(2(1)+,94Mo) symmetric one-phonon states, energy systematics, spins and parities, and comparison with shell model calculations.     

A semi-classical model of multi-step direct and compound nuclear reactions

A semi-classical model of multi-step direct and compound nuclear reactions is proposed to describe the angular distributions of particles emitted from the inelastic scattering induced by a nucleon with an energy of several tens of MeV. The energy-angle correlation is exactly taken into account for the first few steps of the collision process (multi-step direct process) and the generalized master equation is employed for the following stages of collision process, using the energy-averaged kernelG(Ω → Ω′) (multicompound process). The calculations for¹⁹⁷Au(p, p′),¹²⁰Sn(p, p′) and⁹³Nb(n, n′) show that the model can rather nicely reproduce the experimental data of double-differential cross sections.     

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.     

The (d, α) reaction viewed as a two-step process

The ^{98, 97, 94}Mo(d, α)^{96, 95, 92}Nb and ⁹³Nb(d, α)⁹¹Zr reactions have been studied at 12 MeV bombarding energy. A DWBA analysis using one- and two-step processes has been carried out. The two-step process is found, in general, to dominate the one-step and together give rise to cross-section predictions within a factor of 10 of experiment. The angular distribution patterns are found to be best reproduced by DWBA predictions based on certain L-transfers (“parity violating”) associated with only the two-step process and which play but a minor role in their contribution to the overall cross section.     

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.     

Decay scheme of92m Nb

The beta decay of the 2^{+ 92m} Nb was reinvestigated via⁹³Nb(γ, n) reaction. The feeding of the 2⁺ 2,067 keV level of⁹²Zr was determined measuring the intensity of the 1,132 keV gamma-ray transition.