A. D'Onofrio

Stopping power, electron screening and the astrophysical S(E) factor of d(He-3,p)He-4

Abstract The d( 3 He,p) 4 He cross section has been measured at E =4.2 to 13.8 keV using the LUNA underground accelerator facility. The experiment was performed to determine the magnitude of the atomic screening effect and to establish values for the energy loss used in data reduction. The observed stopping power of the 3 He ions in the D 2 target is in good agreement with the standard compilation. Using these stopping power values the data lead to an electron-screening potential energy U e = 132±9 eV, which is significantly higher than the estimated value of 65 eV from an atomic-physics model.

High-energy γ-rays measured in coincidence with α-particles in the reaction 19F + 12C at Elab = 121.7 MeV

The yield of γ-rays emitted in the dissipative reaction 19F + 12C, at Elab = 121.7 MeV has been measured in coincidence with α-particles emitted at θlab = 10°. Comparison with preliminary statistical model calculations shows that assuming only compound nucleaus formation is not sufficient to reproduce the data. Other mechanisms have to be included before information on reaction dynamics can be extracted and definitive conclusions can be drawn.

Identification of high spin states in146Dy throughγ-recoil coincidences

High spin states of146Dy above the 10+ isomer have been identified by means ofγ- recoil andγ}-γ coincidences through the reaction90Zr(58Ni, 2pat a bombarding energy of 250 Me V. The level scheme is discussed in terms of the coupling of 2h11/2protons to the N=80 core vibrations.

Gamma-ray spectroscopy with incomplete fusion reactions for the systems 16O +58,64Ni at 100 Me V

Abstract Energy spectra and angular distributions of ejectiles with 3 ⩽ Z ⩽ 7 have been measured for the reaction 16 O on 64 Ni at 100MeV incident energy. Measured optimum Q -values and cross sections are accounted for by an incomplete fusion model. Coincidences between ejectiles detected at grazing angle and discrete γ-rays have been measured for the reactions 100 MeV 16 O+ 58,64 Ni. The in-plane to out-of-plane anisotropies of discrete γ-rays show a high degree of spin polarization of incomplete fusion residues which can be exploited for spectroscopic studies.

A multiprocessor system for on-line data acquisition, handling and display

Abstract A system for on-line data processing based on a multiprocessor architecture is presented. It has been designed for nuclear and atomic physics experiments requiring multiparametric data acquisition, analysis and display. It allows fast event recognition performed by a special CAMAC module, data acquisition based on automatically generated routines according to user-defined events, on-line integration of raw, calculated and gated parameters. A high resolution colour display is used to show 1-D and 2-D spectra.

Reaction-mechanism evolution for the system 20Ne + 60Ni at intermediate energies: from massive transfer to fragmentation

Abstract Mass and charge distributions for heavy residues in the reaction 20 Ne + 60 Ni at 50 MeV/nucleon were measured by in-beam and off-line γ-ray spectrometry. The stacked foil method was used to obtain information about the distribution of the velocity component parallel to the beam direction for target-like residues. The comparison of the data to the predictions of a participant-spectator model indicates that an 8% width for the dissipated energy distribution accounts for the observed projected ranges.

Energy sharing in binary reactions induced by 19F on 64Ni at 118MeV

Abstract Complex fragments have been detected in singles and in γ-particle coincidence measurements for the 19 F + 64 Ni system, at 118 MeV incident energy. Cross sections for the excited states of the complex fragments were measured detecting the characteristic γ-transitions deexciting these states. The measurement of cross sections for the population of the ground and excited states of 18 O and 13 C, as well as of the production cross sections of heavy residues in coincidence with these ejectiles, as a function of the total dissipated energy, indicate an evolution of energy sharing, with increasing mass transfer, from equipartition to thermal equilibrium.

Ejectile emission in the 120 MeV 30Si + 30Si reaction

Abstract Inclusive emission of ejectiles spanning from He to Ti has been studied in the 120 MeV 30 Si + 30 Si reaction. Indications are presented for the presence of both mechanisms: deep inelastic collisions and incomplete fusion. In particular, most probable energies of projectile-like fragments with 10 ⩽ Z ⩽ 18 are well reproduced by Q -values calculated for deep inelastic collisions in the sticking limit. On the other hand the observation of ejectiles corresponding to large massive transfers with Z Z > 18 suggests the presence of incomplete fusion mechanisms. A comparison between the angle-integrated cross sections of the observed ejectiles and those calculated with a sum-rule model for incomplete fusion is presented.

1H, 4He emission as probe for the shapes of hot composite nuclei: 83Rb at E∗ = 103 MeV

Abstract 1H,4He evaporative emission from the composite nucleus 83Rb at E ∗ = 103 MeV has been analysed in the framework of statistical model for spherical and deformed nuclei by means of two evaporative codes. The dependence of the results on the transmission coefficients used in the calculations is discussed in the frame of a comparison of the two programs. Energy spectra indicate important barrier reductions compared to those for cold spherical nuclei independently from the two codes. Emitter deformations alone cannot give an explanation indicating the need of new physical ingredients in the statistical model.