N. A. Demekhina

Analysis of isomeric ratios in (γ, n) and (γ, p) reactions around giant-resonance energies

Isomeric ratios are investigated in simple photonuclear reactions occurring on targets in the mass range 90–180 amu that are irradiated with 20-to 40-MeV photons. The results of measurements are compared with estimates based on the statistical model of deexcitation of compound nuclei. The isomeric ratios in question are calculated with allowance for special features of photonuclear reactions induced by bremsstrahlung photons and for the properties of nuclear transitions in residual products. The results of these calculations, involving no free parameters, agree satisfactorily with experimental data.

Multimode approximation for 238U photofission at intermediate energies

The yields of products originating from 238U photofission are measured at the bremsstrahlung endpoint energies of 50 and 3500 MeV. Charge and mass distributions of fission fragments are obtained. Symmetric and asymmetric channels in 238U photofission are singled out on the basis of the model of multimode fission. This decomposition makes it possible to estimate the contributions of various fission components and to calculate the fissilities of 238U in the photon-energy regions under study.

Some peculiarities in the interaction of 6He with 197Au and 206Pb

Excitation functions were measured for fusion followed by the evaporation of neutrons in the reactions 206Pb(6He, 2n)210Po and 197Au(6He, xn)203−xnT1, where x = 2−7, as well as for the transfer reactions on a 197Au target with the formation of the 196Au, 198Au, and 199Au isotopes. The experiment was carried out at the Dubna Radioactive Ion Beams (DRIBs) complex of FLNR, JINR. The 6He beam intensity was about 5 × 106 pps, the maximum energy being (60.3 ± 0.4) MeV. A significant increase in the cross section was observed below the Coulomb barrier for the fusion reaction with the evaporation of two neutrons compared to statistical model calculations. Unusual behavior for the production of 198Au is observed, whereas the cross section for the formation of 199Au is very low. The analysis of the data in the framework of the statistical model for the decay of excited nuclei, which took into account the sequential fusion of 6He, has shown good agreement between the experimental and calculated values of the cross sections for the case of sub-Coulomb-barrier fusion in the 206Pb + 6He reaction.

Target residues formed in the 4.4 GeV deuteron-induced reaction on gold

A. R. Balabekyan, N. A. Demekhina, G. S. Karapetyan, D. R. Drnoyan, V.I.Zhemenik, J.Adam, L.Zavorka, A.A.Solnyshkin, V.M.Tsoupko-Sitnikov, J.Khushvaktov, L. Karayan, A. Deppman, V. Guimarães a) Yerevan State University A. Manoogian, 1, 025, Yerevan, Armenia b) Yerevan Physics Institute, Alikhanyan Brothers 2, Yerevan 0036, Armenia Joint Institute for Nuclear Research (JINR), Flerov Laboratory of Nuclear Reactions (LNR), Joliot-Curie 6, Dubna 141980, Moscow region Russia c) Instituto de Fisica, Universidade de São Paulo Rua do Matao, Travessa R 187, 05508-900 São Paulo, SP, Brazil d) Joint Institute for Nuclear Research (JINR), Laboratory of Nuclear Problems (LNP), Joliot-Curie 6, Dubna 141980, Moscow region Russia

Symmetric and asymmetric fission modes in proton-induced fission at 660 MeV of 238U

Fission product cross sections of intermediate-energy fission of 238U were used in order to construct the charge and mass yield distributions. Enriched target of 238U was irradiated by proton beam with energy 660 MeV for several hours at the LNP Phasotron, Joint Institute for Nuclear Research (JINR), Dubna, Russia. The charge distribution of the fission fragments was analyzed for calculation of isobaric cross sections. The mass yield curves were expanded into symmetric and asymmetric components according multimodal fission approach. The fissility values of actinides were calculated at given proton energy. The obtained results have been compared to the same data for targets 237Np and 241Am.

Recoil studies in the reaction of 12C ions with the enriched isotope 118Sn

The recoil properties of the product nuclei from the interaction of 2.2 GeV/nucleon 12C ions from Nuclotron of the Laboratory of High Energies, Joint Institute for Nuclear Research at Dubna with a 118Sn target have been studied via catcher foils method. The experimental data were analyzed using the mathematical formalism of the standard two-step vector model. The results for 12C ions are compared with those for deuterons and protons. Three different Los Alamos versions of the Quark-Gluon String Model were used for comparison with our experimental data.

Properties of products originating from the interaction of 35-MeV/nucleon 7Li ions with Pb nuclei

The results are presented that were obtained by measuring and analyzing the yields and kinematical features of radioactive products of the reactions initiated in a lead target by lithium ions accelerated to an energy of 35M eV per nucleon. The cross sections, charge and mass distributions, and kinematical and energy features of various reaction products associated with the fission and the evaporation channels of the decay of excited nuclei are determined. Quantities that are calculated in the present study include the momenta and kinetic energies of residual nuclei, as well as the momentum transfer and the excitation energy of intermediate nuclear systems formed upon complete and incomplete fusion. On the basis of an analysis of data obtained in our experiment, the total cross section for nuclear interaction and partial widths with respect to various channels of the decay of intermediate compound nuclei are determined in the energy range being investigated.

Formation of isomeric states in (γ, γ′) reactions at energies around the giant dipole resonance

The population of isomeric states in (γ, γ′) photonuclear reactions at energies around the giant dipole resonance is considered for 115In and 180Hf nuclei. The results are compared with previously published experimental and theoretical data. The behavior of the excitation function suggests an increase in the cross section for the formation of high-spin isomeric states in the giant-dipole-resonance region.

Recoil properties of fragments formed in 4.4 GeV deuteron-induced reactions on a gold target

The recoil properties of fragments produced by the interaction of 4.4 GeV deuterons with a

Recoil products from p+118Sn and d+118Sn at 3.65 GeV/A

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