L. Mikhailov

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.

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.

A note on the application of CsI(Tl) counter to light charged particle detection in the spontaneous fission of 252Cf

Emission of light charged particles with Z ≤ 4 and gamma-rays from spontaneous fission of 252Cf has been identified by a scintillator detector based on a CsI(Tl) crystal. The inclusive energy spectra of light charged particles were measured with a low energy threshold ∼ 1.5 meV/A in the presence of an n − γ background. Parameters of p, t, α spectra in triple fission were extracted.