Measurement and analysis of the excitation functions for alpha particle induced reactions on niobium

Stacked foil activation technique and Ge(Li) gamma ray spectroscopy have been used for determining the excitation functions up to 45 MeV, of six reactions⁹³Nb[(α, n), (α, 2n) ^m , (α, 2n) ^g , (α, 3n), (α,p3n) and (α, αn)]. Excitation functions were also calculated theoretically by means of the hybrid model with and without the inclusion of pre-equilibrium emission of particles. A general agreement was found in (α, xn) type of reactions.     

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.     

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.     

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.     

Measurement and analysis of alpha-induced reactions on Ta,Ag and Co

Excitation functions for the reaction¹⁸¹Ta (α,xn)^185−x Re,^107,109Ag (α, ypxn) and⁵⁹Co (α, ypxn) were obtained from measurements of residual activity of stacked foils from threshold to 60 MeV. The excitation functions for the production of¹⁸¹Re,¹⁸²Re,¹⁸³Re,¹⁸⁴Re,¹⁰⁵Ag,¹¹¹In,⁵⁴Mn,⁵⁶Co,⁵⁸Co, and⁶⁰Co, are being presented. The experimental data are compared with calculations considering equilibrium as well as pre-equilibrium reactions according to the hybrid model of Blann. High energy part of the excitation functions is dominated by the pre-equilibrium reaction mechanism. Calculations were done using a priori calculational method of Overlaid Alice Code of Blann. Most of the excitation functions in the energy range mentioned above could be very well fitted with the hybrid model calculation for exciton numbern=4 withn _p=2 andn _n=2. The overall agreement with theory is good. Certain discrepancies, however, indicate the necessity to revise the hybrid model with respect to emission of complex particles.     

Excitation functions of alpha particle induced reactions on aluminium and copper

Cross-sections for the reactions with product nuclei²⁴Na,²²Na,⁶⁸Ga and⁶⁷Ga were investigated over the energy range of 30 to 75 MeV for alpha particle induced reactions on natural aluminium and copper, using stacked-foil activation technique. The measured excitation functions were analysed with special reference to their suitability for monitoring beam energy and intensity. The experimental results were compared with the predictions of hybrid model of Blann. The assumption of initial exciton numbern ₀=4(4p0h) best satisfies the measured excitation functions in the present work.     

Measurement and hybrid-model analysis of proton-induced reactions with V,Fe and Co

On target elements V, Fe and Co (natural isotopic composition) proton-induced reactions were investigated in the energy region from 12 to 45 MeV using the stacked-foil technique. The product nuclides observed were ⁴⁸Cr, ⁴⁹Cr, ⁵¹Cr, ⁴⁸V, ^{46m + g}Sc, ⁴⁷Sc and ⁴⁸Sc from V, ⁵⁵Co, ⁵⁶Co, ⁵⁷Co, ^{58m + g}Co, ⁵²Fe, ^{52m + g}Mn, ⁵⁴Mn, ⁵¹Cr and ⁴⁸V from Fe, and ⁵⁶Ni, ⁵⁷Ni, ⁵⁶Co, ⁵⁷Co, ^{58m + g}Co, ⁵⁴Mn and ⁵⁶Mn from Co. The comprehensive set of excitation functions extending and improving earlier studies is compared with calculations considering equilibrium as well as preequilibrium reactions according to the hybrid model of Blann. The overall agreement between experiment and theory is good. Certain discrepancies, however, indicate the necessity to revise the hybrid model with respect to the emission of complex particles.     

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.     

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.     

Analysis of the excitation functions of (α, xnyp) reactions on natural copper

Excitation functions of the reactions⁶³Cu[(α, n), (α, 2n)+(α, pn)] and⁶⁵Cu[(α, n), (α, 2n), (α, 3n), (α, 4n)+(α, p3n)] were investigated up to 50 MeV using stacked foil activation technique and Ge(Li) gamma ray spectroscopy method. Since natural copper used as the target has two odd-mass stable isotopes of abundance,⁶³Cu(69.17%) and⁶⁵Cu(30.83%), their activation in some cases, gives the same residual nucleus through different reaction channels but with very different threshold energies. In such cases, the individual reaction cross sections are separated with the ratio of theoretical cross sections. The experimental results were compared with the predictions of preequilibrium hybrid model of Blann. A general agreement was found in all reactions using initial exciton numbern ₀=4(4p0h) and also preequilibrium fraction depends on the incident particle energy.     

201 MeV proton excitation of giant resonances in 208Pb: Macroscopic and microscopic analysis

The region of the giant resonances in ²⁰⁸Pb has been investigated by inelastic scattering of 201 MeV protons. To test the analysis, angular distributions were measured for the low-lying 3^?, 5^?, 2⁺ and 4⁺ collective states. The giant isoscalar quadrupole resonance (ISGQR) is split into two structures, one at 9.0 MeV with a full width at half-maximum Γ = 1.0 MeV, the other one at 10.6 MeV (Γ = 2.0 MeV), with fine structures at 8.9, 9.3, 10.1, 10.6 and 11 MeV. A macroscopic analysis using the distorted-wave Born approximation (DWBA) leads for the low-lying collective levels, as well as for the ISGQR, to transition probabilities too small by a factor of two, compared with those obtained in other reactions. Microscopic analysis using the distorted-wave impulse approximation (DWIA), with three different sets of random phase approximation (RPA) transition densities, is in very good agreement with the data. At forward angles, in the 12 to 16 MeV excitation energy region, a strong resonance at 13.5 MeV (Γ = 3.6 MeV) is accounted for by the Coulomb excitation of the isovector giant dipole resonance (IVGDR); at larger angles the results are compatible with the excitation of the isoscalar monopole resonance (ISGMR) located at 13.9 MeV (Γ = 2.6 MeV).A resonance located at 21.5 MeV (Γ = 5.7 MeV) appears as the superposition of an isovector quadrupole resonance (IVGQR) excited by Coulomb interaction and a resonance of multipolarity L = 1 ΔT = 0 (ISGDR “squeezing mode”).     

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.     

Measurement and analysis of excitation functions for alpha induced reactions on iodine and cesium

The excitation functions for the reactions¹²⁷I(α, 2n)¹²⁹Cs,¹²⁷I(α, 4n)¹²⁷Cs,¹³³Cs(α, 2n)¹³⁵La and¹³³Cs(α, 4n)¹³³La have been measured up to ≈50 MeVα-particle energy using the stacked foil activation technique. Measured excitation functions are compared with pre-equilibrium geometry dependent hybrid model calculations. It has been found that theoretical calculations using an initial exciton numbern ₀=4 (2p+2n+0h) give good agreement with experimental excitation functions.     

Measurement of excitation functions and mean projected recoil ranges of nuclei in12C-induced reactions on vanadium

Excitation function and mean projected recoil ranges of nuclei produced in the¹²C-induced reactions on⁵¹V target were measured by conventional stacked foil and thick-target thick-recoil-catcher technique for bombarding energiesE ≤ 84 MeV for¹²C ion beam. The measured recoil ranges are converted to momentum transfer. Information on momentum transfer was used to get clues about some aspects of the interaction such as complete fusion which corresponds to full momentum transfer and incomplete fusion reaction mechanism. The measured excitation functions are compared with the calculation based on the statistical model which describes only equilibrium decay of the compound nucleus using the Cascade code and the geometry dependent hybrid model which describes equilibrium as well as pre-equilibrium decay of the compound nucleus using the Alice/91 code. The measured excitation functions and average ranges of the radioisotope products of the reactions¹²C on⁵¹V indicate that the three separate reaction mechanisms could be attributable to complete fusion of¹²C, incomplete fusion of⁸Be and incomplete fusion of⁴He respectively with the target. The⁸Be and⁴He are the break-up component of¹²C into⁸Be +⁴He. The predictions of the codes, especially the Cascade, generally agree with the measured cross-sections which could be attributed to complete fusion of¹²C with the target⁵¹V.     

Investigation of spin dependence of neutron cross sections and of strength functions for rare earth nuclei in experiments with polarized neutrons and nuclei

Experiments on the spin dependence of the interaction of resonance neutrons (up to 100 keV) with the rare earth nuclei ¹⁴¹Pr, ¹⁵⁹Tb, ¹⁶⁵Ho, ¹⁶⁷Er and ¹⁶⁹Tm are reported. The measurements were performed with polarized neutrons and nuclei. The spin dependence of S-wave strength functions was investigated, and the imaginary part of the spin-spin potential (W_ss = 0.10 ± 0.06 MeV) was estimated in optical-model calculations with a potential in the form of a rectangular well. The energy dependence of the difference of strength functions for two J-states shows possible intermediate states in the formation of the compound nucleus. The J-values of about 230 resonances were determined.     

Angular and energy dependences of emission probability for light particles in 22Ne-induced reactions at 8 MeV/nucleon

Inclusive energy spectra and angular distributions have been measured for light charged particles with Z = 1–4 emitted in the interaction of ²²Ne ions with a ¹⁸¹Ta target. The reaction products were analysed and detected by means of a system of ΔE-E telescopes placed in the focal plane of a magnetic spectrometer. The end-point energies of the light particles correspond to the calculated kinematic limits taking into account the rotational energy of the residual nucleus. The angular distributions of the high-energy particles are strongly forward peaked. The data obtained are analysed on the basis of the moving source, rotating hot spot, massive transfer and breakup fusion models. The relative yields of the different isotopes and their most probable energies are described by the massive transfer model. The qualitative behaviour of the spectra in the vicinity of the kinematic limits can be explained in terms of the breakup fusion model.     

Angular distributions for target residues in reactions of 14N and 12C with 115In

Mechanisms of the reactions of ¹²C and ¹⁴N with ¹¹⁵In have been investigated by measuring the angular distributions of the target residues. Various possible transfer mechanisms are discussed with the help of kinematic analysis and a semiclassical transfer model. Interesting secondary (or tertiary) peaks are seen near 90 in the angular distributions for most target residues.     

Hybrid model analysis of the excitation function for alpha induced reaction on121Sb and123Sb

Excitation functions for the reactions¹²¹Sb(α, xn)^125−x I,¹²³Sb(α, xn)^127−x I and¹²¹Sb(α, p3n)¹²¹Te were obtained from the measurements of the residual activity of stacked foils of antimony trioxide evaporated on Al backings from threshold to 60 MeV. The excitation functions for the production of¹²¹I,¹²³I,¹²⁴I,¹²⁶I and¹²¹Te are presented. The experimental data are compared with calculations considering equilibrium as well as pre-equilibrium reaction mechanism according to the hybrid model of Blann. The high energy part of the excitation functions are dominated by the pre-equilibrium reaction mechanism. Calculations were done using a priori calculational method of Overlaid Alice Code of Blann. Most of the excitation functions in the energy range mentioned above could very well be fitted with the hybrid model calculation for exciton numbern=4 withn _n=2 andn _p=2. The overall agreement with the theory is good. Certain discrepancies for example¹²¹Sb(α, p3n)¹²¹Te excitation function, indicate that the production mechanism is different from the one presumed for the calculation.     

Equilibrium and pre-equilibrium emissions in proton-induced reactions on <Superscript>203,205</Superscript>Tl

In this study, the excitation functions for the reactions ²⁰³Tl(p, n)²⁰³Pb, ²⁰⁵Tl(p, 3n)²⁰³Pb, ²⁰³Tl(p, 2n)²⁰²Pb, ²⁰⁵Tl(p, 4n)²⁰²Pb, ²⁰³Tl(p, 3n)²⁰¹Pb, ²⁰⁵Tl(p, 5n)²⁰¹Pb, ²⁰³Tl(p, 4n)²⁰⁰Pb and ²⁰⁵Tl(p, 6n)²⁰⁰Pb have been calculated using pre-equilibrium and equilibrium reaction mechanisms. Calculated results based on hybrid model, geometry-dependent hybrid model and cascade-exciton model have been compared with the experimental data.