Nb Reaction Research Articles

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.

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.

Incomplete fusion mechanism in 16O + 93Nb reaction at 6 MeV/nucleon: Recoil range measurements

Summary Recoil range distribution of evaporation residues formed in complete and incomplete fusion of 96 MeV 16O with 93Nb has been measured by recoil catcher technique followed by off-line gamma-ray spectrometry. The cross sections for complete and incomplete fusion were delineated from the earlier measured excitation function data at the same beam energy. The results show that incomplete fusion is associated with angular momentum values close to the critical angular momentum for complete fusion of the projectile and target.

Structure in multiplicity gated proton spectra in low energy 12C + 93Nb reaction—compound nuclear process or massive cluster transfer?

Gamma multiplicity gated proton spectra have been measured in the 12C + 93Nb reaction at E ( C 12 ) = 40 MeV at backward angles. The shape of the spectrum shows a drastic change with the increase in multiplicity acquiring a broad structure at proton energies beyond ∼ 15 MeV corroborating our earlier measurements at E ( C 12 ) = 42.5 MeV . Measurements made in coincidence with residue γ rays, detected in an array of eight HPGe clover detectors, confirm these observations. An excitation energy and angular momentum-dependent enhancement of the nuclear level density or a massive cluster transfer of 11B to the 93Nb can explain the data.

Cross-section measurements for (n, 2n), (n, p) and (n, α) reactions on strontium isotopes at the neutron energy about 14 MeV

Cross-sections for 84Sr(n, 2n) 83Sr, 86Sr(n, 2n) 85mSr, 86Sr(n, 2n) 85Sr, 88Sr(n, 2n) 87mSr, 84Sr(n, p) 84Rb, 86Sr(n, p) 86Rb, 88Sr(n, p) 88Rb and 88Sr(n, α) 85mKr reactions have been measured at neutron energies from 13.5 to 14.6 MeV using activation technique and by means of γ-ray spectrometry. The neutron flux was determined using the monitor reaction 93Nb(n, 2n) 92mNb and the neutron energies were measured by the method of cross-section ratios for 90Zr(n, 2n) 89Zr to 93Nb (n, 2n) 92mNb reactions. The results of present work are compared with data published previously.

Identification of mixed-symmetry states in odd- A 93Nb

Following the acceptance for publication of the paper entitled Identification of mixed-symmetry states in odd-A93 Nb, the authors realized that some mistakes in the data analysis had occurred. As mentioned in thori ginal paper, from an experiment using the 94 Zr (p ,2n)93 Nb reaction, multipolarities and spin assignments were deter mined. The de-excited γ -rays were detected using the HORUS spectrometer, comprised of 16 H PGe detectors. Here, nine correlation groups are available in order to determine the spins through angular -correlation analysis. Later, the auth ors realised that there was a problem with the efficiency of the correlation groups where the cluster detector was prim arily involved. This problem led to unreliable quadrupole mixing ratios, δ, and therefore to the incorrect iden tication of mixed -symmetry states. Th e problem has been resolved by using only seven correlation groups. At present, the authors cannot confirm the identication of any mixed-symmetry states since the data are being reanalised. The new analysis and conclusions of this work will be published in a forthcoming paper.

Cross-section measurements for (n, 2n) and (n, p) reactions on platinum isotopes in the neutron energy range of 13.5 to 14.6 MeV

Abstract Cross-sections for (n,2n) and (n,p) reactions have been measured on platinum isotopes at the neutron energies of 13.5 to 14.6 MeV using the activation technique. Data are reported for the following reactions: 198Pt(n,2n)197m+gPt, 198Pt(n,2n)197mPt, 192Pt(n,2n) 191Pt, 190Pt(n,2n) 189Pt, 196Pt(n,2n)195mPt+195Pt(n,n ′)195mPt, 194Pt (n,p) 194Ir, 195Pt(n,p)195mIr and 196Pt(n,p)196mIr. The neutron fluences were determined using the monitor reaction 93Nb(n,2n)92mNb or 27Al(n,α) 24Na.

Momentum-dependent mean field in π0 production in Nb + Nb collisions

The Boltzmann-Nordheim-Vlasov (BNV) equation has been solved by using a microscopic momentum-dependent (MD) nuclear mean field. This potential has been calculated in the framework of the self-consistent Brueckner theory up to the second order in the G-matrix. Comparison with the so-called soft and stiff Equation of State (EOS) is presented, using the Skyrme force. Calculations have been performed for the 93Nb + 93Nb reaction at Elab = 100, 250, 400A MeV. Our results show that the subthreshold π0 production cross-section is very sensitive to the momentum-dependent mean field, resulting, at the lowest energy, in a total cross-section a factor of 7 larger than that obtained with a local potential. The effect decreases as the bombarding energy increases.

$\alpha$ -decay spectroscopy of light odd-odd Bi isotopes - II: 186Bi and the new nuclide 184Bi

Alpha-decay of the new nuclide 184Bi has been studied in the complete-fusion reaction 93Nb(94Mo, 3n)184Bi at the velocity filter SHIP. The evaporation residues were separated in-flight and subsequently identified on the basis of recoil- $\alpha$ , recoil- $\alpha$ - $\gamma$ analysis and excitation functions measurements. Two $\alpha$ -decaying isomeric states in 184Bi with half-life values of 13(2) ms and 6.6(1.5) ms were identified. The $\alpha$ -branching ratio of 180Tl was deduced for the first time as $b_\alpha = (2 --12)\%$ . Improved data on the fine-structure $\alpha$ -decay of 186Bi were obtained in the 93Nb(95Mo, 2n)186Bi reaction. A similarity of the decay energies and half-life values of 184,186Bi is pointed out and a possible explanation for this effect is suggested.

Cross-section measurements for (n, 2n), (n, p) and (n, n′ α) reactions on gallium isotopes in the neutron energy range of 13.5–14.6 MeV

Cross-sections for (n, 2n), (n, p) and (n, n′ α) reactions have been measured on gallium isotopes at the neutron energies of 13.5–14.6 MeV using the activation technique. Data are reported for the following reactions: 69Ga(n, 2n) 68Ga, 69Ga(n, p) 69mZn, 71Ga(n, p) 71mZn, and 71Ga(n, n′ α) 67Cu. The neutron fluences were determined using the monitor reaction 93Nb(n, 2n) 92mNb.

Broad structure in multiplicity gated proton spectra in 12C+ 93Nb reaction at E( 12C)=42.5 MeV

High-energy proton spectra in the energy range E p c.m.∼8.5–25 MeV are measured in the reaction 12C+ 93Nb at E lab( 12C)=42.5 MeV and at laboratory angles of 130°, 145° and 160°. The spectra, recorded in coincidence with a gamma ray multiplicity detector array, show a broad structure which becomes more prominent at higher multiplicity. The centroid of the structure shifts with multiplicity. These features could arise from an unusual spin and excitation energy dependence of the nuclear level density in Pd and Ag nuclei with mass around A=104. However, a non-statistical process, viz., the massive cluster transfer, cannot be ruled out.

Measurement of the natMo(n, x) 94Nb cross section using ultra low-level γ-ray spectrometry at HADES

The cross section for the natMo(n, x) 94Nb reaction was measured in the energy range from 14.5 to 20.3 MeV using both conventional γ-rayspectrometry and the ultra low-level γ-ray spectrometry (ULGS) facility in the underground laboratory HADES. The exceptionally long half-life of the activation product 94Nb of 20300 years required a long irradiation, a large sample and a special irradiation geometry, to allow a simultaneous determination of the three data points. This measurement presents the first data above 14 MeV. The data are well described by model calculations with the STAPRE-H code that include the 94 Mo(n, p) 94 Nb and 95 Mo(n, np) 94 Nb reactions.

Nuclear orbiting and anomalies in nuclear reactions

In this paper, we report our measurements of back-angle oxygen and carbon particle yields from 16O+89Y, 12C+93Nb reactions forming the same compound nucleus 105Ag at the same excitation energy and spin distribution. We find anomalously large oxygen yield and entrance channel dependence at high excitation energies from 16O+89Y reaction implying formation of a dinuclear orbiting complex. Possible connection between nuclear orbiting and fast fission is also discussed.

Slow nuclear decoherence: possibilities to detect the decay of thermalized-nonequilibrated matter

The statistical reactions with memory approach suggests the possibility of forming thermalized-nonequilibrated matter in nucleon-induced reactions. Unlike the fully equilibrated compound nucleus of Bohr, the decay of the thermalized-nonequilibrated system is characterised by the forward peaking of the evaporating particles and the significant spontaneous channel–channel correlation. This correlation results in the nonself-averaging of the excitation function fluctuations in the evaporation domain of the spectra offering a new possibility to experimentally detect the slow nuclear decoherence and the decay of the thermalized-nonequilibrated matter. The quantitative estimation of the effect for the 93 Nb(n,p) reaction at E n ≃14 MeV yields ≃30–40% for the relative magnitude of fluctuations at the maximum, E p ≃6–8 MeV, of the proton evaporation spectrum.

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.

Quasiparticle Driving Effect on Shape of 87Nb Soft Nucleus

The high spin states of 87 Nb have been studied by using the 58 Ni (32 S , 3p)87 Nb reaction at beam energy 95–105 MeV and the reaction 58 Ni (35 Cl , 2pα) at 124 MeV. γ-γ coincidence relations, angular distributions of γ-rays, excitation functions and DCO ratios were measured. High spin states in 87 Nb have been established up to spin of 37/2ℏ and excitation energy of 7 MeV. CSM calculation was carried out with parameters of configuration dependence of nuclear shape. The nature and configuration of every band in 87 Nb are discussed.

Electrochemical characterization of thin passive films on Nb electrodes in H3PO4 solutions

The electrical and semiconducting properties of thin anodic passive films potentiostatically formed (1 V £ Ef £ 5 V vs. sce) on polycrystalline niobium electrodes in aqueous 0.5 mol/L H3PO4 solutions (pH 1.3) were studied, at room temperature, using electrochemical impedance spectroscopy. The data were analysed with a transfer function using a non-linear fitting routine, assuming that the resistance of the film is coupled in series with the faradaic impedance of the Nb(0) Nb(V) reaction, and these in parallel with the capacitance of the passive film/electrolyte interface. The relative permittivity of the films was estimated as about 44. The number concentration of donors (N D) in the films was found to decrease with Ef (i.e., with increasing film thickness). A flat band potential value of -0.72 V was also obtained from Mott-Schottky plots.

Transitions in nuclear disassembly as viewed by fragment charge correlations.

Central heavy-ion collisions in the (nearly) symmetric entrance channels {sup 20}Ne+{sup 27}Al, {sup 40}Ar+{sup 45}Sc, {sup 87}Kr+{sup 93}Nb, and {sup 129}Xe+{sup 139}La have been systematically studied at many intermediate beam energies. The relative sizes of the three largest fragments in the central events are studied using new variables defined from charge Dalitz plots. Autocorrelations between these variables and the method used to select the central events are investigated. Also described are the hidden constraints on these variables that are imposed by definition. For increasing beam energies, the average values of these variables imply transitions from sequential binary disassembly to multifragmentation at beam energies of {similar_to}50 and {similar_to}30 MeV/nucleon in the {sup 40}Ar+{sup 45}Sc and {sup 129}Xe+{sup 139}La entrance channels, respectively. Similar trends are observed for the central {sup 20}Ne+{sup 27}Al and {sup 87}Kr+{sup 93}Nb reactions.

Linking of direct and compound chains in multistep nuclear reactions.

We remove the sharp separation between multistep compound and multistep direct emission in the Feshbach-Kerman-Koonin (FKK) derivation of preequilibrium processes. In addition to the original multistep compound mechanism, we find a new class of multistep processes arising from linking of the direct and compound chains. There can be additional scatterings in unbound [ital P] space before the quasibound compound [ital Q] space is entered, or after it is left. We provide a theoretical justification for the presence of [ital P][r arrow][ital Q] transitions, which are needed to account for experimentally observed preequilibrium spectra. Our formalism is applied to the analysis of the 14 MeV [sup 93]Nb([ital n],[ital n][prime]) reaction, using modified distorted-wave Born approximation (DWBA) matrix elements which include an inverse [ital S]-matrix factor. Since the dominant contribution to multistep compound emission comes from the 2[ital p]1[ital h] [ital Q] stage, the linking of the multistep chains results in flux bypassing this stage, resulting in a reduced multistep compound emission and an increased emission from the compound nucleus.

Nuclear dynamics for heavy ion collisions with a momentum dependent potential

Abstract The Boltzmann-Nordheim-Vlasov equation has been solved by using a microscopic momentum dependent (MD) nuclear mean field. This potential has been calculated in the framework of the self consistent Brueckner theory up to the second order in the G -matrix. Comparison with the so called soft and stiff Equation of State (EOS) is presented, using the Skyrme force. The calculations have been performed for 40 Ca+ 40 Ca and 93 Nb+ 93 Nb reactions, from the balance energy up to E lab =800 A MeV. At variance with the MD phenomenological potentials, the results at higher energy show that our soft EOS with MD mean field gives predictions which do not differ very much from the soft EOS with Skyrme potential without momentum dependence. On the other hand, at lower energy the MD potential has a behaviour which is quite different from both soft and stiff EOS, especially as far as the balance energy is concerned.