Search

The excitation temperature is measured in an argon-CO/sub 2/ thermal plasma by optical emission spectroscopy. The theoretical calculations of concentration used to determine excitation temperature and also the numerical Abel inversion are presented. The effect of CO/sub 2/ molecule upon this plasma is studied as a function of the Ar-CO/sub 2/ mixture composition and discharge current. The excitation temperature is ranging from 7000 K to 11000 K, and excitation temperature gradient from 200 K/mm to 600 K/mm.

A theoretical model for calculating the temperature distribution inside the body of an insulating material brought in contact with an electric arc is elaborated. From this model, and from experimental temperature measurements inside different materials, an original method for selecting insulating materials for breaker chambers is developed. >

The excitation of theΔ resonance is observed in proton collisions on C, Nb and Pb targets at 0.8 and 1.6 GeV incident energies. The mass E0 and widthΓ of the resonance are determined from the invariant mass spectra of correlated (p, π±)-pairs in the final state of the collision: The mass E0 is smaller than that of the free resonance, however by comparing to intra-nuclear cascade calculations, this reduction is traced back to the effects of Fermi motion, NN scattering and pion reabsorption in nuclear matter.

Two-proton correlation functions at small relative momentum have been systematically studied with the large solid angle detector DIOGENE at Saturne for interactions induced by Ne and Ar beams on various targets, and incident energies per nucleon ranging from 200 to 1000 MeV. From these distributions, informations on the space-time structure of the source have been derived as a function of the centrality of the collision, the target-projectile combinations and the incident energy, using the model of Koonin. Special attention has been devoted to take into account all experimental biases in order to get the distorted theoretical correlation curves before comparison to the experimental data. Other interesting conclusions have been obtained when comparing the extracted source radii to the dimensions of the overlapping volume of target by projectile in a pure geometrical model of the collision (clean cut geometry). Some results concerning fragment-fragment small angle correlations are also presented.

Triple-differential cross sections of proton-like particles were obtained for Ne+NaF, Ne+Nb and Ne+Pb reactions at 800 MeV per nucleon from quasi-exclusive measurements. Their dependence upon the azimuthal angle with respect to the reaction plane is analyzed. In addition to the usual flow pattern, another component of the azimuthal dependence is observed. It can be parametrized using the second order parameters in Fourier series expansion. The dependence of this component upon transverse momentum, rapidity and impact parameter (multiplicity) is investigated.

Emission of light fragments at small angles is studied in relativistic heavy ion collisions using the Diogene plastic wall for both symmetrical and non-symmetrical target-projectile systems with 400 MeV per nucleon and 800 MeV per nucleon incident neon nuclei. Efficiency of multiplicity measurements in the small angle range for the selection of central or peripheral collisions is confirmed for asymmetric systems. Differential production cross sections of Z = 1 fragments show evidence for the existence of two emitting sources. The apparent temperature of each source is obtained from comparison with a thermodynamical model.

The momentum distributions with respect to the reaction plane for charged pions emitted in Ne-nucleus and Ar-nucleus collisions have been measured with the 4 π detector Diogene at the Saturn synchrotron. The reaction plane is estimated from the baryon momenta, using a standard technique for flow analysis. The pions exhibit a non-zero flow. For asymmetric systems, there is a preferential emission in the direction of the lighter (projectile) nucleus. Such a behaviour contradicts the predictions of INC calculations and is underestimated by QMD calculations which include mean field effects. It can be interpreted with a simple geometrical model in terms of absorption by the spectator nuclear matter.

In order to study the nuclear collective flow, the triple differential momentum distributions of charged baryons are fitted to a simple anisotropic gaussian distribution, within an acceptance which removes most of the spectator contribution. The adjusted flow angle and aspect ratios are corrected for systematic errors in the determination of the reaction plane. This method has been tested with Monte Carlo simulations and applied to experimental results and intranuclear cascade simulations of argon-nucleus collisions at 400 MeV per nucleon.

Diogene, an electronic 4 pi detector, has been built and installed at the Saturne synchrotron in Saclay. The forward angular range (0 degree-6 degrees) is covered by 48 time-of-flight scintillator telescopes that provide charge identification. The trajectories of fragments emitted at larger angles are recorded in a cylindrical 0.4-m3 Pictorial Drift Chamber (PDC) surrounding the target. The PDC is inside a 1-T magnetic field; the axis of the PDC cylinder and the magnetic field are parallel to the beam. Good identification has been obtained for both positive and negative pi mesons and for hydrogen and helium isotopes. Multiplicities in relativistic nucleus-nucleus reactions up to 40 have been detected, limited mainly by the present electronics.

Proton-proton small angle correlations have been measured in neon-nucleus collisions, using the 4 pi detector Diogene, at 400 and 800 MeV per nucleon incident energies. Values of the size of the emitting region are obtained by comparison with the Koonin formula, taking into account the biases of the apparatus. The dependence of the density on target mass and incident energy is also analysed.

Electromagnetic processes at low momentum transfer are often sources of background in many experiments. To be removed these effects must be calculated by the experimentalist, who must have a good knowledge of the validity of the theoretical formulas that he must use. Then we thought that it will be useful to prepare this review whose presentation is such that it should allow everyone to appreciate the accuracy of formulas that the must use in very complex situations. In this paper, we examine the problem related to bremsstrahlung, pair production and radiative corrections. The first part is devoted to kinematic and to the methods used to establish the corresponding cross sections Mise au point sur la theorie et l'experience en ce qui concerne les phenomenes electromagnetiques a faible transfert d'impulsion, qui apparaissent souvent comme des phenomenes parasites: rayonnement de freinage, production de paires e + e − , corrections radiatives. Cinematiques des processus et methodes de determination des sections efficaces

The collective flow measurements presented in this lecture have been performed with the DIOGENE electronic 4π-detector1 installed at the Saturne synchrotron in Saclay, which can deliver beams up to mass 40. In order to study the properties of dense (and hot) nuclear matter, it is required to measure nucleus-nucleus collisions involving a large number of nucleons That is the reason why we focused our experiment on asymmetric collisions,, with target nuclei heavier than the beam.

Experimental results concerning proton production in nuclear collisions, obtained at Saturne with the Diogene 4π facility, are compared with the predictions of a thermodynamical model, using collective velocity distributions combined with a statistical thermodynamics in local rest frames. Experimental differential cross sections for alpha + nucleus and Neon + nucleus central collisions at incident energies between 200 and 800 MeV per nucleon are well reproduced by the model, for an angular range 30–110 degrees in the laboratory system. Extracted values of the temperatures are compared with those given by other authors.

Mean multiplicities of pi+ and pi- in 4He collisions with C, Cu, and Pb at 200, 600, and 800 MeV/u, and with C and Pb at 400 MeV/u have been measured using the large solid angle detector Diogene. The independence of pion multiplicity on projectile incident energy, target mass and proton multiplicity is studied in comparison with intra-nuclear cascade predictions. The discrepancy between experimental results and theory is pointed out and discussed.

Triple-differential cross sections of charged pions were measured for collisions of Ne projectiles at E/A = 800 MeV with NaF, Nb, and Pb targets. The reaction plane was estimated event by event from the light-baryon momentum distribution. For heavy targets, preferential emission of charged pions away from the interaction zone towards the projectile side was observed in the transverse direction. Such a preferential emission, which is not predicted by cascade calculations, may be attributed to a stronger pion absorption by the heavier spectator remnant.