Yu. A. Muzychka

Complete and incomplete fusion of 6Li ions with Bi and Pt

Experimental excitation functions are presented for fusion–evaporation and transfer reactions in the interaction of 6Li with Bi and Pt targets. The data on the cross sections obtained for the produced evaporation residues are in agreement with calculations within the framework of the statistical model using the ALICE-MP code. Enhancement of the cross section for deuteron transfer reactions is observed at energies below the Coulomb barrier. The results are discussed from the point of view of how the nuclear cluster structure influences the probability of interaction at near-barrier energies.

Shell effects and cross sections of formation of neutron-deficient isotopes of Ac, Ra and Fr in 20Ne + 197Au reaction

Abstract The cross sections of the formation of Ac-, Ra- and Fr-evaporation residues in the 20 Ne + 197 Au reaction have been measured by means of the VASSILISSA kinematic separator in the range of the compound-nuclei excitation energies from 40 to 120 MeV. The experimental data have been analyzed on the basis of the statistical model of excited nuclei decay. The influence of different assumptions about the parameters of fission barriers on calculation results was considered.

Excitation functions for complete-fusion and transfer reactions in 4He interaction with 197Au nuclei

Excitation functions are measured for the fusion reactions 197Au(4He, xn)201−xnTl that are induced by alpha-particle interaction with gold nuclei in the energy range 14–36 MeV and in which x neutrons (0 ≤ x ≤ 3) are evaporated. The stack-activation technique was used to record and separate reaction products. Experimental data on the fusion reactions followed by evaporation of one to three neutrons agree with results of previous studies. For the radiative-capture reaction 197Au(4He,γ)201Tl, the upper limit on the cross section proved to be much lower. The excitation functions for the reactions subjected to measurements are compared with the results of calculations based on the statistical model and with the results of an experiment performed previously in a 6He beam.

The excitation functions of complete and incomplete fusion reactions of 6Li with Pt nuclei

Experimental results from measuring the energy dependences of cross sections of fusion and transfer reactions for 6Li beams and Pt targets are presented. The experiments were performed using the MSP-144 magnetic analyzer; stacks of platinum foils were installed at the focal plane of this analyzer. In the energy range 22.5–42.5 MeV, the energy resolution of the beam hitting the target stack was not worse than 0.25 MeV and that of the transmitted beam was not worse than 0.40 MeV. The yields of products of neutron and deuteron transfer reaction on target nuclei were measured using the γ activity induced in the platinum targets. Thus, excitation functions for transfer reactions were obtained in a wide energy range, including near the Coulomb barrier. It was shown that the basic reaction channel is the deuteron capture from 6Li. In this case, the maximum of the excitation function for 6Li breakup and subsequent deuteron capture lies near the Coulomb barrier of the reaction.

Study of fusion and nucleon transfer channels in the 197 Au + 6 He reaction in an energy range of 6 He to 20 Mev/A

New data on the cross sections of reactions occurring during the interaction of 6He nuclei with 197Au at energies of 6He from 40 to 120 MeV are presented. The experiments were performed in the ACCULINNA secondary beam separator of the Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research. To identify the reaction products, the activation method for measuring the gamma activity of the target assembly of thin foils was used. The excitation functions for fusion reactions involving the evaporation of up to ten neutrons from the compound nucleus as well as reactions with the emission of charged particles and nucleon transfer in the investigated energy region are obtained. Data analysis was carried out using two codes: ALICE-MP and NRV. The cross sections for the (6He, xn) reactions occurring through the compound nucleus are mostly in agreement with the results of model calculations based on the statistical approach. It is shown that, up to the energies of 114 MeV, the cross-section drop in the complete fusion reactions is negligible. The experimental excitation functions of reactions leading to the formation of isotopes of mercury and gold (transfer reaction) indicate that the main contribution to their formation is made by direct processes and that evaporation reactions (6He, pxn) and (6He, αxn) play a minor role, as is evidenced by a comparison of the measured cross sections with the calculation results.

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.

Investigating the nuclear fusion and nucleon transfer channels in the 197Au + 6He reaction at 6He energies up to 20 MeV/A

New data on the cross sections of reactions that proceed during the interaction of 6He and 197Au nuclei in the 6He energy range of 40 to 120 MeV are reported. The experiments were performed using the secondary beam of the ACCULINNA separator at the Flerov Laboratory of Nuclear Reactions (FLNR), JINR. Reaction products are identified by means of activation method to measure the gamma activity of a thin-foil target assembly. Excitation functions for 6He fusion reactions with subsequent emission of up to 10 neutrons from the compound nucleus are measured. Cross sections for reactions with emission of charged particles and nucleon transfer were also measured. The experimental cross sections for the (6He, xn) reactions that proceed via the formation of a compound nucleus agree in general with calculations using models that involve the statistical approach. It is shown that the complete fusion reaction cross section drops slightly up to an energy of 114 MeV. The experimental excitation functions for the reactions resulting in the formation of mercury and gold isotopes indicate that the main contribution to their formation comes from direct processes, while the evaporation reactions (6He, pxn) and (6He, αxn) are of minor importance.

Above-barrier enhancement of fusion in the 6He + 209Bi nuclear reaction

The fission cross sections for the 6He + 209Bi reaction as functions of the 6He-beam energy are measured. The experimental excitation functions for the reaction 209Bi(6He, 4n)211 At are also presented. The 6He secondary ion beam is obtained on the basis of the extracted-beam transport system of the U400-M accelerator (the Q4DQ spectrometer). A comparison of the experimental data obtained with available results for the 6He + 209Bi reaction shows that a pronounced enhancement of the fission cross sections in the above-barrier energy region is observed in the case of the reaction with the 6He beam. In order to fit the results of theoretical calculations to the experimental data, it is necessary to reduce the Coulomb barrier by 15% (20%). This corresponds to an increase of 1.5 (1.6) fm in the parameter r0 of the nuclear potential.

Excitation Functions for Complete Fusion and Transfer Reactions in the Interaction of 6 He with 197 Au Nuclei

The excitation functions for the fusion reactions with subsequent neutron evaporation, 197Au(6He, xn)203 − xnTl (x = 2−7), and the neutron transfer reactions with production of the 196Au and 198Au isotopes have been measured. Unusually high cross section of the 198Au isotope production at energies below the Coulomb barrier has been observed. Possible mechanisms of production and decay of the transfer reaction products are considered.

Studies of formation of fusion evaporation residues with Z≥83 in heavy ion reactions

By employing the kinematic separator VASSILISSA and the beams of 20,22Ne, 24,26Mg, 40Ar and 40Ca we studied 18 projectile‐target combinations leading to formation of compound nuclei with atomic numbers 83‐102 and obtained xn, pxn, and αxn evaporation residues in the range of the projectile energy extending from the Coulomb barrier to the values corresponding to the compound nucleus excitation of about 100 MeV. The systematics is presented of the maximum xn reaction cross‐sections which are governed by the fissility of the reaction products. As a result, the values of macroscopic fission barriers were extracted for the neutron‐deficient nuclides in the range of Z=83–92 and N=104–134. These values are discussed in terms of contrasting with predictions of the rotating droplet model. Three isotopes, 252,253,254102, were obtained as deexcitation products of the 258102 compound nucleus formed by 22Ne and 26Mg projectiles. Some conclusions are drawn from these results about the possible use of 22Ne and 26Mg beam...