V. Yu. Ugryumov

Total cross sections for 4,6He + 28Si reactions measured at 10–28 MeV/A

New results on the energy dependence of the total cross section (σR) for 6He scattering on 28Si in the incident energy range 10–28 MeV/A are obtained. The α-particle-production cross sections for the 28Si(6He, 4He)X channel are measured as well. The secondary beam of 6He with an intensity of up to 5×104 particle/s was generated by bombarding a thick beryllium target with ∼32-MeV/A7Li ions. In the energy region below 17 MeV/A, σR increases sharply. The experimental dependences of the total cross sections are compared with the results of σR calculations using the double-folding potential within the optical model. The energy dependence of σR for 6He differs from that for the neighboring nuclei, which can be associated with the structural features of the former nucleus. The energy spectra of α particles produced in the 6He interactions with silicon indicate two mechanisms of their production: transfer reaction and 6He breakup in the field of the 28Si nucleus.

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.

Energy dependence of the total cross section for the reaction of 4He ions with silicon nuclei

Directly measured data on the total cross section for the reaction of projectile 4He ions with silicon nuclei at energies below 25 MeV/nucleon are presented. The energy dependence of the parameters of a semimicroscopic potential is determined from the measured values of this cross section. This investigation was performed at the Flerov Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research (Dubna, Russia) and at the Department of Physics at the University of Jyväskylä (Finland).

Total reaction cross section from the interaction of 4He ions with 28Si at 10–30 MeV

New results have been obtained for the energy dependence of the total reaction cross section σR of 4He on 28Si in the energy range Eα ≤ 30 meV.

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.