Search

Events with 2, 3 and 4 heavy fragments (A≥20) detected in the reactions100Mo +100Mo at 18.7, 23.7 A·MeV and120Sn +120Sn at 18.4 A·MeV were analyzed by means of an improved version of the kinematic coincidence method. The phase-space distributions prove that 3- (and possibly 4-) body events predominantly originate from a two-step mechanism and are compatible with the hypothesis of a binary deep-inelastic interaction followed by the further fissionlike decay of one (or both) of the primary fragments. The characteristics of the fission step — mass asymmetry, relative velocity, in-plane and out-of-plane angles — have been reconstructed for the 3-body events and indications are found that nonequilibrium effects at the end of the deep-inelastic phase may influence the fissionlike decay.

Experimental and theoretical evidence is presented that the proton exchange is strongly enhanced by a mixing of single-particle configurations in $^{37}\mathrm{Cl}$ (in the system $^{36}\mathrm{S}$${+}^{37}$Cl, which is shown to be the clearest example of hybridization in nuclear physics. The experimental data on elastic and inelastic transfer are only reproduced if the complete set of single-particle states (${\mathit{d}}_{3/2}$,${\mathit{s}}_{1/2}$,${\mathit{f}}_{7/2}$,${\mathit{p}}_{3/2}$,${\mathit{f}}_{5/2}$, and ${\mathit{p}}_{1/2}$) is included in a coupled-reaction-channel calculation. The strong enhancement is explained by the hybridization of orbits of different parity. In a two-center molecular-orbital approach the density of the proton orbitals in the lowest state is shown to be concentrated at the center between the two $^{36}\mathrm{S}$ cores.

Angular distributions of elastic scattering of 58 Ni by 64 Ni and inelastic scattering leading to the first 2 + state in 58 Ni or in 64 Ni have been measured at E lab =203.8 and 219.2 MeV. The data have been analyzed in the frame of the folding model. A renormalization N of the folding potential consistently lower than unity ( N ≈ 0.65) is needed to reproduce the elastic-scattering data. Coupled-channel calculations including the main inelastic channels explain partly this discrepancy. They reproduce the elastic- and inelastic-scattering data with a renormalization of N ≈ 0.8 at both energies. Interference between Coulomb and nuclear excitation is shown to play an important role in the repulsive character of the polarization potential.

Triple and four-fold coincidences among fragments have been measured in the reaction 84 Kr+Au at 43 MeV/u. All events showing the projectile-like nucleus and fission fragments of the target-like nucleus, and all events with one additional intermediate-velocity fragment, were analysed in the frame of a dissipative collision and a participant-spectator model. The mechanism is basically that of a dissipative collision but the emission of the intermediate velocity fragment by the target differs from an equilibrated evaporation.

XYZt is a multidetector specially designed to measure intermediate-mass fragments emitted at small angles (2° E A > 20 MeV/u . It consists of 12 independent modules which can be placed in any geometry. Each module is composed of an avalanche counter measuring time and position, and an ionisation chamber measuring an energy-loss. XYZt allows coincidence measurements in an angular range extending below the grazing angle. In experiments performed at GANIL, it detects Z > 4 fragments, separates the charges up to Z = 15, has a time resolution better than 1 ns and is transparent to light particles.

Elastic scattering of 35Cl and 37Cl on 24Mg was measured at two c.m. energies. Optical model analysis with different potentials are compared. Isotopics effects on absorption are observed. The closure approximation model is found to give a good reproduction of experimental data.

Nous avons étudié les distributions angulaires de la réaction 9Be( 3He, α)8Be* (1+) formant les niveaux de 17,64 MeV et 18,15 MeV à 4, 5 et 7 MeV. L'allure des courbes est semblable pour les deux niveaux, le rapport de leur section efficace de formation est de l'ordre de 2 et ne dépend pas de l'énergie incidente. Nous donnons les résultats d'une analyse en DWBA et nous discutons le mélange de spin isobarique de ces niveaux.

Angular distributions for the elastic scattering of 32 S on 40 Ca have been measured at 32 S bombarding energies of 100, 120 and 151.5 MeV. Optical model analyses were performed using Woods-Saxon and double-folding potentials which yield a good description of the angular distributions. The energy dependence of the phenomenological optical potentials and renormal- ization coefficients of the double-folded potential were found. These results are anomalous in comparison with the elastic scattering of heavy projectiles (with A > 12) on the same target nucleus.

The one-proton and one-neutron transfer reactions in the interaction of 34 S with incident 32 S were studied in the 0–3.5 MeV excitation energy range of the exit nuclei. The experimental set-up (kinematic identification technique, implanted targets, etc.) has allowed an angular resolution of 0.2°, a mass resolution of 1.5% and a Q -value resolution of 0.35 MeV. Comparison with DWBA computations using an analytical approximation for the radial integral, with insertion of suitable recoil corrections, demonstrates the absorptive direct mechanisms of the reactions, even when double excitation of residual nuclei is present. The extracted values for the products of spectroscopic factors are in very good agreement with the known values and they are confirmed by EFR-DWBA computations. The selectivities of the reaction receive about the same contributions from the nuclear structure as from the specific reaction mechanism.

Experimental data of elastic scattering between nuclei of various structures on a large energy scale has been analysed in the framework of the folding model by use of the complex effective interaction of Faessler et al . (1981). A general good reproduction of the data is obtained if renormalization coefficients for the real and the imaginary parts of the optical potential are introduced. The application of the dispersion relation of Mahaux et al . (1986) allows to reproduce the observed energy dependence of the real part of the potential.

The elastic scattering differential cross section for 32 S incident on 33 S at E inc = 91.3 MeV has been measured. The observed backward oscillations are successfully described by explicit inclusion of a parity-dependent term in the real potential for the optical-model calculations of the elastic scattering. To investigate possible sources of the parity-dependent term, the backward oscillations were also interpreted as being produced by the interference between the elastic amplitude and the one-neutron elastic one-step transfer process.

La réaction 9Be(3He, α) a été étudiée entre 4 et 10 MeV. L'analyse des courbes d'excitation et des distributions angulaires met en évidence la prépondérance d'un mécanisme de noyau composé en dessous de 7 MeV et un mécanisme de pick-up d'un neutron j = 3/2 aux énergies incidentes supérieures à 7 MeV. La compilation des résultats acquis dans le domaine d'excitation du 12C et en particulier sur les résonances géantes multipolaires du 12C permet d'interpréter la structure résonnante observée à 29,5 MeV par l'excitation de composantes isoscalaires (3-, 4+) de ces résonances.

Detailed large-angle angular distributions have been measured for 28Si(32S, 32S)28Si and 28Si(32S, 36Ar)24Mg reactions from Ec.m. = 42.0 to 48.1 MeV in steps of 0.23 MeV. Excitation functions of cross sections for 6 groups display very weak structure of intermediate width. A comprehensive analysis revealed no statistically significant deviations in the excitation functions, which, however, display considerable levels of correlation suggestive of strong coupling. No intermediate-width resonances were found. Results of optical-model calculations suggest that the elastic scattering angular distributions may be strongly influenced by the 4He transfer mechanism which may also be responsible for the wide window for L = 18 observed in the elastic data.

The mutual excitation of projectile and target was measured for 32 S + 28 Si scattering at 90 and 97.01 MeV on a large angular range. A coupled channel analysis of the angular distributions is in good agreement with the data. It is used to demonstrate the important interference of simultaneous and sequential excitation amplitudes and the sensitivity of this process to the nuclear surface shape.

Angular distributions for the 32 S( 32 S, 32 S) elastic scattering have been measured at 70, 90, 97.09, 120 and 160 MeV incident lab-energies. The data have been analyzed with the folding model, using the M3Y and DDD interactions. A good reproduction of the data is obtained if a renormalization coefficient for the real part of the optical potential is introduced. Moreover the application of the dispersion relation proposed by Mahaux et al . and which uses the imaginary part does not seem to give renormalization coefficients as important as those found in the analysis of the data.

The elastic scattering of 32S+32S at 90 MeV and 32S+40Ca at 100 MeV has been analysed in the framework of the folding model by the complex-effective (CE) interaction of Faessler and others (1983). The results have been compared with a previous analysis in terms of the M3Y interaction of Bertch and his co-workers (1977). It has been found that the CE interaction gives almost equivalent results to the M3Y interaction.

A rapid description of this reaction chamber with emphasis on its original elements is given. These special characteristics are: 1. three movable detectors with continuously variable solid-angle; 2. target storage box in vacuum; 3. short-lived radioactive source lock; 4. beam centering system.

At low incident energy and 90 deg (lab. angle) the level at 4.52 Mev (T = 0) of /sup 6/Li is not found. Only one level at 5.47 plus or minus 0.04 Mev is seen in the neighborhood of 5.5 Mev. (auth)

An alpha - alpha coincidence method is used to detect the particles coming from the breakup of /sup 8/Be in the 16.626 and 16.921 Mev excited states. The 18.826 Mev /sup 8/Be stafe has T = 1. The observed breakup does not flt the isobaric-spin conservation rule. (auth)

A bidimensional data acquisition system on paper with two buffer memories is described and dead time losses are calculated as a function of the counting rate.

Les auteurs donnent un nouveau schéma des cinq premiers niveaux excités de lithium 6 déduit de l'étude spectroscopique de la réaction 7Li( 3He, α)6Li entre 1 et 12 MeV d'énergie incidente et de l'interprétation de la diffusion résonnante 4He + d dans le formalisme de la matrice S. Ils présentent un essai d'interprétation du mécanisme de la première réaction dans l'approximation de Born en ondes distordues (D.W.B.A.).

Elastic, inelastic and mutual excitation angular distributions have been measured for 32S+ 24Mg at 65, 75, 56.3, 95 and 110 MeV of 32S incident energy. The data have been analysed by optical model and coupled channel calculations. Energy-dependent optical potentials have been obtained which have been used to describe the 32S + 24Mg fusion data of Berkowitz et al2). Barrier penetration and coupled channel models are compared. It is found that the energy-dependence of the empirical potentials is essential if a consistent simultaneous description of elastic, inelastic an fusion data is required.

Publisher Summary This chapter discusses the energy dependent deviations from the Barshay–Temmer symmetry. In isospin-multiplet production, Barshay and Temmer have predicted symmetry of angular distributions about 90o in the case of unique and conserved isospin. The largest deviation from this symmetry has been observed in the D(α,t) 3He reaction at 48.25 MeV. The corresponding triton energy for the inverse reaction would have been 3.5 MeV. In the experiment described in the chapter, elastically scattered tritons were absorbed by 70u aluminum foils, and particle identification was achieved by dE-E multiplication technique. Relative differential cross sections were obtained by normalizing the counting rates of the monitor, and absolute cross sections were measured to an accuracy of about 30% in a separate run with a modified geometry of the Faraday cup. The chapter also highlights the angular distributions and the size of its points, which exceeds statistical errors. The angular distributions show a characteristic bell-shaped pattern.

The elastic and inelastic cross sections of 32 S on 28 Si at 77, 90 and 97.09 MeV incident energies have been measured. The excitation of the first 2 + and 3 − levels in both nuclei as well as the [2 1 + , 2 1 + ] mutual excitation were studied. The angular distributions are reproduced by coupled-channel calculations. The influence of various reaction mechanisms have been studied. Strong high-order effects are predicted. Total reaction and inelastic cross sections for low-lying excited states have been extracted.

Nous donnons ici des valeurs de la section efficace de la reaction D + D → p + T au-dessous de 15 MeV au moyen d'une cible epaisse dans laquelle le deuterium est occlus. La connaissance de ces sections efficaces est necessaire dans les calculs thermonucleaires.

On donne un rappel d'une publication anterieure (ref. 6). D'autre part, un nouveau dispositif experimental est decrit, permettant l'etude de la cassure du 8Be en 2α succedant a sa formation par la reaction 7Li(d, n)8Be. Des resultats preliminaires relatifs au niveau de 16,67 MeV du 8Be sont signales.