A. Dacal

Streamer chamber experiments

Abstract The reactions 40 Ar + KCl at eight energies from 0.36 to 1.8 GeV/u, 4 He + KCl at 977 and 40 Ar + Balg and 40 Ar + Pb 3 O 4 at 772 GeV/u measured in a Streamer Chamber experiment have been analyzed to determine the stopping power of nuclei, the degree of isotropy and thermalization achieved in central collisions, to search for collective expansion effects and to obtain compressional energies of bulk nuclear matter. Observables used were pion and proton exclusive final state measurements, ratios of total transverse to longitudinal momentum per event, momentum flux and Λ production. From the systematic discrepancy of the π − multiplicities produced in central collisions with respect to an intranuclear cascade model, compressional energies are extracted which fit a parabolic form of the nuclear matter equation of state with a compressibility constant of K = 240 MeV.

Yrast levels in 27Al suggested by resonance structure in the 12C(15N, α) reaction☆

Abstract A large number of correlated resonances with ∼400 keV (c.m.) widths were observed in addition to statistical fluctuations in the 12 C( 15 N,α) reaction. The resonant portion of the cross section suggest the population of high-spin levels close to the yrast line of the compound nucleus.

Study of the coherence widths Γ in 28Si measured by the 12C(16O, α) reaction

Abstract States in 24 Mg were populated by the 12 C( 16 O, α) 24 Mg reaction. Excitation functions were measured in the bombarding energy range E c.m. = 17.1–19.7 MeV for states in 24 Mg with excitation energies from 0 to 12 MeV. A fluctuation analysis of the excitation functions was made and the coherence widths Γ of the compound nuclear states were extracted. By comparing theoretical calculations of Γ with present and previous measurements values for the moment of inertia and the spin cutoff parameter of 28 Si were extracted.

Coherence widths in 27Al measured with the 12c(15n, α) reaction

Abstract Excitation functions for the 12 C( 15 N, α) reaction have been measured at θ lab = 7°,in200 keV steps from E 15 N = 21.4–39.0 MeV. A total of forty-one states were observed in 23 Na with excitation energies from 0 to 12.5 MeV. The analysis of the excitation functions reveals the presence of statistical and non-statistical components. The coherence widths Γ were extracted from the statistical fluctuations. By comparing measured and theoretical widths, values for the spin-cutoff and moment-of-inertia parameters were extracted for the compound system 27 Al. It is also shown that the choice of the Hauser-Feshbach denominator for the calculation of Γ does not affect significantly the slope of the curve Γ versus the excitation energy in the compound system if E x .

Compression Effects in Relativistic Nucleus-Nucleus Collisions

The negative pion multiplicity is measured for inelastic and central collisions of 40Ar with KCl at eight energies from 0.36 to 1.8 GeV/nucleon and for 4He and 40Ar on BaI2 at 977 and 772 MeV/nucleon, respectively. A systematic discrepancy in central collision data with a cascade model calculation which fits proton- and pion-nucleus cross sections but omits potential energy effects is used to derive the energy going into bulk compression of the system. A value of the compressibility constant of K = 240 MeV is extracted in a parabolic form of the nuclear matter equation of state.

Preliminary Results with the Reaction 84Kr on 27Al at E/A = 15 MeV Using the HILI

The study of heavy-ion collisions in the energy regime between 10 and 100 MeV/u is a useful tool to explore the mechanisms that arise as the bombarding energy increases. It has been reported that the complete fusion cross section which is dominant at low energy central collisions decreases to the benefit of processes of more binary character[1] This feature leads to the following questions. At what energy does such transfer from fusion mechanism to binary mechanisms occur? Is this “transition energy” system dependent? To what extent does the binary process persist? Evidences of binary processes at energies around 30MeV/u and higher have been reported in experimental studies[2, 3, 4, 5, 6] Another feature that appears when the bombarding energy of the reaction is increased is the production of intermediate mass fragments (IMF’s). The mechanisms and sources reponsible for IMF production are still open questions. With our study of the 79Br on 27A1 at 11.8 MeV/u and 84Kr on 27A1 at 15 MeV/u systems we intend to explore some of these questions.

Energy Calibration of Intermediate Mass Fragments from the 930-MeV 79Br on 27Al Reaction

The intermediate mass fragments produced in the reaction 79Br on 27Al at 930 MeV have been characterized using the Heavy Ion Light Ion (HILI) detector.1 Their laboratory energy has been determined using two different approaches.

Coincidences between light particles, evaporation residues, and complex fragments emitted in the reaction {sup 58}Ni + {sup 58}Ni at 500 MeV bombarding energy

Light particles (protons and alphas) were measured in coincidence with complex fragments (4 40) using the large detector array HILI. A {sup 58}Ni beam of 500 MeV extracted from the HHIRF tandem accelerator was used to bombard a {sup 58}Ni target of 99% enrichment. A good account of the proton and alpha spectra in coincidences with the residues can be achieved only by including in the statistical model calculation the emission of complex fragments and allowing a small emission of a dinuclear configuration formed prior to fusion. The relative kinetic energy spectra between the complex fragments and the residues show a typical Coulomb peak consistent with emission from the compound nucleus and the out of plane angular correlation shows that the emission is coplanar.

Energy dependence of multinucleon transfer reactions induced by 20Ne on 12C

Abstract The energy dependence of up to five nucleon transfer reactions induced by 20 Ne on 12 C has been measured in the energy range 150 to 294 MeV. Good agreement is found between the experiment and both DWBA and semiclassical calculations.