Elastic electron scattering on Zr and Mo

Elastic electron scattering on ⁹⁰Zr and ⁹²Mo has been measured at 200 and 300 MeV up to 2 fm⁻¹ momentum transfer. Data analysis led us to adopt the parabolic Gaussian shape as a valuable charge distribution for these nuclei. For ⁹⁰Zr, we have compared this model with charge distributions given by recent Hartree-Fock calculations.     

Experimental study of excitation functions and isomer ratios for 211, 212Po

Excitation functions have been measured for ground states and isomers populated in the ²⁰⁸Pb(α, n)²¹¹Po, ²⁰⁹Bi(α, np)²¹¹Po, ²⁰⁹Bi(α, p)²¹²Po and ²⁰⁹Bi(α, n)²¹²At reactions for α-beams ranging from 45 MeV to 172.5 MeV. The experimental results have been compared with theoretical calculations assuming direct and preequilibrium reaction mechanisms, respectively. It is found that the experimental excitation functions can be reproduced satisfactorily by calculations in the framework of the preequilibrium model. Isomer ratios have been extracted from the data as well. Their energy dependence can be reproduced by an optical-model calculation for beam energies larger than about 60 MeV.     

Evaporation residue excitation functions for 35Cl induced reactions of 112, 120Sn and 141Pr

Evaporation residue excitation functions have been measured for ³⁵Cl ions up to 170 MeV (lab) on targets of ^{112, 120}Sn and ¹⁴¹Pr. These values are combined with previously reported fission excitation functions to give fusion excitation functions. Classical analysis of these results yield fusion barriers and fusion radii. Earlier results are confirmed: as the target atomic number increases the required density penetration at the fusion barrier increases. The percentage of the reaction cross section undergoing fusion monotonically decreases as the targets go from ²⁷Al to ¹⁴¹Pr. The nuclear contribution to the fusion barrier deduced from these measurements is compared with several model predictions and is found to be in satisfactory agreement with the models due to Bass and Krappe and Nix.     

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.     

Investigation of 38Ar levels by 37Cl+p reactions: (I). Yield curves,excitation energies and branching ratios

Yield measurements have been performed on the reactions ³⁷Cl(p, p₀)³⁷Cl, ³⁷Cl(p, α₀)³⁴S (E_p = 1.17–1.70 MeV) and ³⁷Cl(p, n₀)³⁷Ar, ³⁷Cl(p.γ)³⁸Ar (E_p = 0.64–2.92 MeV); detailed investigations are restricted to resonances below E_p = 1.79 MeV. Resonance energies, strengths and (some) widths are reported for 12, 26 and 247 resonances in the reactions (p, p₀), (p, n₀) and (p, γ), respectively.Simultaneous (p, α₀) and (p, γ) yield measurements over selected E_p intervals in the E_p = 0.88–1.64 MeV range established the existence of 42 resonances decaying by both γ and α₀ emission. Analysis of the γ-ray spectra of 100 ³⁷Cl(p, γ)³⁸Ar resonances leads to precision excitation energies (ΔE_x = 0.1–2 keV) of 57 bound states (E_x < 8 MeV) and branching ratios of the resonances and of 50 bound states.     

Measurement and interpretation of heavy ion fusion excitation functions

Fusion excitation functions for ³²S induced reactions on ²⁴Mg, ²⁷Al, ⁴⁰Ca and ⁵⁸Ni are reported at incident ³²S ion energies of 65 to 132.5 MeV. Measurements were made using counter-telescopes with beams from Van de Graaff accelerators. From these data barrier heights and radii for fusion are extracted. These results are interpreted in terms of the nuclear diftuseness, and the nuclear attractive potentials at the fusion radii are deduced. Relative density overlaps at the fusion radius are estimated from electron scattering density distributions. Several parameterizations for the fusion radii and barrier heights are presented. Fusion cross sections are compared with reaction cross sections based on elastic scattering measurements coupled with optical model analysis. It is found that for the systems investigated, 90±10 % of the reaction cross section results in fusion.     

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.     

Measurement and analysis of excitation functions for alpha-induced reactions in copper

Excitation functions for the production of⁶⁸Ga,⁶⁷Ga,⁶⁶Ga,⁶⁵Ga +⁶⁵Zn and⁶¹Cu fromα-induced reactions in natural copper have been measured in the energy range ≈ 10–40 MeV using the stacked foil technique. A stack of nine copper foils was irradiated by a 40 MeVα-beam. Theγ-rays emitted from the irradiated samples were recorded. Excitation functions have also been calculated theoretically using a statistical model with and without the inclusion of pre-equilibrium emission of particles. Pre-equilibrium component simulated by exciton model shows that the inclusion of pre-equilibrium emission gives better agreement between experimental and theoretical excitation functions. Pre-equilibrium fraction depends on the incident energy and the target mass number.     

Fusion excitation functions near and below the Coulomb barrier for symmetric and asymmetric medium-mass systems

Fusion excitation functions for the systems ¹²C + ^{46, 48, 50}Ti, ^{28, 30}Si + ³⁰Si and ¹⁸O + ⁴⁴Ca have been determined at energies near and below the Coulomb barrier. Inelastic excitation functions for the targets ^{48, 50}Ti and ⁴⁴Ca have been also measured in the same energy range. The absolute cross sections were obtained by in-beam γ-ray spectroscopy technique using a rotating target. Fusion cross sections ranging in magnitude from ～ 0.3 mb to ～ 1300 mb were determined with an accuracy of 10–20%. The fusion excitation functions are analysed in the frame of a semiclassical barrier-penetration model. From the analysis, the height, the radius and the curvature of the fusion barrier for the different systems are extracted. The fusion cross sections are compared with the calculations performed using different heavy-ion potentials. The enhancement of the cross sections at sub-Coulomb energies can be reproduced with a one-dimensional barrier-penetration model taking into account the zero-point motion of the surface of the reaction partners. The fusion cross section of the system ¹⁸O + ⁴⁴Ca is well reproduced by quantum-mechanical calculations, introducing a new degree of freedom taking into account the formation of a neck during the fusion process.     

(3He, 2n) excitation functions for some light nuclei

Excitation functions have been measured for the reaction ⁹Be(³He, 2n)¹⁰C over the range $\text{E(}{}^3\text{He}\text{) = 10–41}\text{MeV}$ and for the reaction ²⁷Al(³He, 2n)²⁸P over the range $\text{E(}{}^3\text{He}\text{) = 14–41}$ MeV by detecting β-delayed γ-rays. An excitation function has also been measured for the reaction ²⁴Mg(³He, 2n)²⁵Si over the range $\text{E(}{}^3\text{He}\text{) = 21–43}\text{MeV}$ by detecting β-delayed protons.     

Excitation functions of some neutron threshold reactions on isotopes of molybdenum

Cross sections were measured for (n,p) reactions on ^{92, 95, 96, 97, 98}mo, (n, α) reactions on ^{92, 98}Mo, and (n, 2n) reaction on ¹⁰⁰Mo for the first time in the neutron energy range of 5.9 to 9.6 MeV. The quasi-monoenergetic neutrons were produced via the ²H(d, n)³He reaction using a deuterium gas target at a compact cyclotron. Use was made of the activation technique in combination with high-resolution γ-ray spectroscopy. Some systematic trends observed in the excitation functions are discussed. For the various isotopes of molybdenum, with increasing mass of the target nucleus, the thresholds of (n,p) and (n,α) reactions increase and the magnitudes of cross sections near the maxima of the excitation functions appear to decrease. Hauser-Feshbach calculations show that in general the excitation functions of (n, p) and (n, α) reactions are described within a factor of 2 by the statistical model only up to about 8 MeV; the (n,2n) reaction on ¹⁰⁰Mo, however, is reproduced well from threshold up to 15 MeV by this model.     

Analysis of (particle,xn) reactions on tantalum and gold: (II). 181Ta, 197Au(3He,xn) excitation functions and equilibrium statistical model analysis

Excitation functions for the reactions ${}^{197}\text{Au}\text{(}{}^3\text{He}\text{, x}\text{n}\text{)}{}^{\mathrm{200?x}}\text{Tl}\text{(x = 3, … 7)}$ and ${}^{181}\text{Ta}\text{(}{}^3\text{He}\text{, x}\text{n}\text{)}{}^{\mathrm{184?x}}\text{Re}\text{(x = 3, … 7)}$ were measured at bombarding energies up to 75 MeV. The data are compared to the results of an equilibrium statistical model calculation including angular momentum conservation and γ-ray competition. Satisfactory agreement was found except for the high energy tails.     

Elastic and inelastic scattering of 15 MeV polarized deuterons from isotopes of Ca,Cu, Sr,Zr, and Mo

The elastic and inelastic scattering of 15 MeV polarized deuterons from ⁴⁸Ca, ⁶³Cu, ⁸⁸Sr, ⁹⁰Zr, ⁹²Zr, and ⁹²Mo has been investigated. Angular distributions of the cross section and vector analyzing power iT₁₁ have been measured for all these nuclei; the tensor analyzing powers T₂₀ and T₂₂ have been studied for ⁹²Zr. Cross sections and vector analyzing powers are generally well explained by the optical model for elastic scattering and by the DWBA with a macroscopic form factor for the inelastic scattering; this is consistent with previous work. Distributions for ⁴⁸Ca, however, are poorly fitted. Anomalous behavior of the N = 50 nuclei found in the inelastic scattering of polarized protons is not present for deuterons. Tensor analyzing powers are not well explained by standard procedures: use of approximate folding model optical parameters did not improve the fits. The distribution of iT₁₁ for the $\text{1}\text{2}$^? state in ⁶³Cu is significantly different from the distributions for the $\text{5}\text{2}$^? and $\text{7}\text{2}$^? states.     

Optical model analysis of proton elastic scattering excitation functions around A = 90

Excitation functions of protons elastically scattered from ⁸⁸Sr, ⁸⁹Y, ⁹⁰Zr and ⁹²Mo over an energy range from 8 to 15 MeV were analysed with the optical model. The deep minima exhibited by these excitation functions especially at extreme backward angles can be described by an imaginary potential which is smaller than that of Becchetti and Greenlees. Compound nucleus contributions were taken into account by appropriate weighting of the data. The magnitude of these contributions in the minima could thus be estimated.     

Study of the reactions 118Sn(d,t) and98Mo(d,t): (I). Spectroscopy of 117Sn and 97Mo

The vector analyzing power and differential cross section have been measured at a deuteron energy of 12.0 MeV for ${}^{118}\text{Sn}\text{(}\text{d}\text{,}\text{t}\text{)}$ transitions to six states of ¹¹⁷Sn (E_x = 0.0, 0.16, 0.31, 0.71, 1.02 and 1.18 MeV), for ${}^{98}\text{Mo}\text{(}\text{d}\text{,}\text{t}\text{)}$ transitions to eight states of ⁹⁷Mo (E_x = 0.0, 0.68, 0.72, 0.89, 1.12, 1.28, 2.39 and 2.52 MeV), and for ${}^{118}\text{Sn}\text{(}\text{d}\text{,}\text{d}\text{)}\text{and}{}^{98}\text{Mo}\text{(}\text{d}\text{,}\text{d}\text{)}$. Deuteron optical model potentials were obtained from analysis of the elastic scattering measurements, and were used in a DWBA analysis of the $\text{(}\text{d}\text{,}\text{t}\text{)}$ results. Comparison of the measurements and DWBA predictions for σ(θ) and for iT₁₁(θ) allows unambiguous determination of tl_n and j_n for all ¹¹⁸Sn(d, t) and most ⁹⁸Mo(d, t) transitions. Differences in the triton energy relative to the Coulomb barrier cause marked qualitative differences in the measured cross sections and analyzing powers between ${}^{118}\text{Sn}\text{(}\text{d}\text{,}\text{t}\text{)}\text{and}{}^{98}\text{Mo}\text{(}\text{d}\text{,}\text{t}\text{)}$ transitions of the same l_n and j_n.     

Thermonuclear reaction rates for proton induced reactions on 41K and neutron induced reactions on 41Ca

The yield of γ-rays from the reaction ⁴¹K(p, γ)⁴²Ca has been measured as a function of bombarding energy over the range 0.68–2.48 MeV and from the reaction ⁴¹K(p, αγ)³⁸Ar over the range 1.20–2.48 MeV, and the yield of neutrons from the reaction ⁴¹K(p, n)⁴¹Ca has been measured from threshold to a bombarding energy of 2.48 MeV. The energy dependence of the cross sections is compared with statistical-model calculations with global optical-model parameters in all particle channels. The calculations seriously overestimate the cross section for the neutron channel and underestimate those for the other channels. A reduction in the imaginary well depth in the neutron channel leads to good agreement with all the data. Statistical-model calculations with this modified set of parameters are then carried out to provide cross sections for the astrophysically interesting reactions ⁴¹Ca(n, p)⁴¹K, ⁴¹Ca(n, α)³⁸Ar, and ⁴¹Ca(n, γ)⁴²Ca. Thermonuclear reaction rates are calculated for all six reactions over the temperature range 5 × 10⁸–10¹⁰K which includes the range of temperatures of interest in nucleosynthesis calculations.     

Resonant structures in the excitation functions of elastic and inelastic scattering of 16O on 24Mg

Excitation functions of ²⁴Mg(¹⁶O, ¹⁶O)²⁴Mg were studied between 25 and 64 MeV incident energy. A strongly resonant behaviour was observed for inelastic scattering at backward angles. The data were analysed in terms of coupled channel calculations. While agreement was good at forward angles, at backward angles the calculated cross sections are an order of magnitude too low suggesting that another reaction mechanism or neglected terms in the heavy ion interaction potential are important.     

Branching ratios for stopped pions in deuterium

The ratios $\text{S =}\text{ω(π}{}^{\mathrm{?}}\text{d}\text{→}\text{nn}\text{)}\text{ω(π}{}^{\mathrm{?}}\text{d}\text{→}\text{nn}\text{γ)}$ has been measured for negative pions stopping in deuterium gas at pressures up to 100 atm. The result is S = 2.83 ± 0.04 which is a factor of two more accurate than previous measurements.     

The neutron total and capture cross sections of 92, 94Zr

The neutron total and capture cross sections of^92,94Zr have been measured at the 80 and 40 m flight stations, respectively, on the Oak Ridge Electron Linear Accelerator (ORELA). Resonance analysis of the total cross sections gave values of s, $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ strength functions. Strong intermediate structure was observed in the $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ cross section of ⁹²Zr. Significant single particle transitions identified in the p-wave capture cross section indicate the importance of the valence process for both nuclei. It is noted that the intermediate structure in the $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ total cross section leads to enhanced valence effects in the capture cross section. The effects of non statistical E1 transitions following particle-hole annihilation in the compound states were not observed in either the ⁹²Zr or ⁹⁴Zr capture cross sections as they had been in that for ⁹⁰Zr.     

Search for giant spin-flip transitions in 90Zr and 208Pb

We have searched for the giant magnetic dipole resonance in ⁹⁰Zr and an associated state in ²⁰⁸Pb. Among the experimental techniques employed in this search was the detection of inelastically scattered protons in coincidence with ground-state de-excitation γ-rays, No state in ⁹⁰Zr up to an excitation of 10.5 MeV or in ²⁰⁸Pb between 5.0 to 6.0 MeV was observed with the desired characteristics. In ⁹⁰Zr, heretofore unidentified levels at 5.51, 5.89 and 6.42 MeV were determined to have J^π = 1^?. In ²⁰⁸Pb J^π = 1^? states were observed at 5.29, 5.51 and 5.94 MeV. The implications of our observations are discussed.